View larger. | Artist’s concept of the Wolf-Rayet 104 pinwheel star system. A new study confirms 2 massive stars are orbiting each other, producing a giant spiral composed of hydrocarbon dust. The study also shows the poles of the stars are not oriented directly toward us as 1st thought, so there is little to no danger of a gamma-ray burst from them hitting Earth, if one of the stars explodes in a supernova. Image via W. M. Keck Observatory/ Adam Makarenko.
Wolf-Rayet 104 is a star system where two massive stars orbit each other. A huge spiral of dust circles around the stars, making it a rare pinwheel star system.
The pinwheel faces right toward us, so astronomers thought the poles of the stars did also. This could present a danger to Earth. Why? If one of the stars exploded in a supernova, it could send a powerful gamma-ray burst directly toward our solar system.
But that isn’t likely to happen, new research from the Keck Observatory shows. The stars’ poles are tilted so much that any gamma-ray burst coming from them would miss us.
Meet Wolf-Rayet 104, the ‘pinwheel death star’
Wolf-Rayet 104 is a famous, rare type of star system known as a pinwheel star. Discovered in 1999, astronomers suspected it consists of two massive stars orbiting each other. As the stars orbit, their stellar winds collide, producing huge amounts of dust. The dust rotates in a giant pinwheel shape. Astronomers using the W. M. Keck Observatory in Hawaii said on March 18, 2025, that they have now confirmed the pair of stars. In addition, they also determined there is little to no danger of Wolf-Rayet 104 emitting a dangerous gamma-ray burst directly toward Earth, as astronomers had previously thought could happen. So the pinwheel death star will seemingly spare us from extinction. Phew!
Astronomer Grant Hill at the Keck Observatory is the author of the latest peer-reviewed research paper. He originally published it in the Monthly Notices of the Royal Astronomical Society on September 19, 2024. Keck issued the new press release on March 18, 2025.
Astronomers discovered Wolf-Rayet 104 back in 1999. It is a rare pinwheel star system due to the huge spiral formation of dust circling a pair of stars. Scientists now suspect it’s actually a triple system, with a third much more distant star connected by gravity. But the pinwheel effect is created by the two main stars. The first of the two is a Wolf-Rayet star. Those stars are hot, bright and massive. Its stellar wind, similar to our sun’s solar wind, is rich in carbon. The other star, an OB star, is even more massive, and its solar wind is mostly hydrogen.
The stellar winds are huge streams of charged particles, or plasmas, flowing out from each star. As the two stars orbit each other, their stellar winds collide, forming hydrocarbon dust. That dust rotates in a giant pinwheel shape around the stars, and it glows brightly in infrared.
Is Wolf-Rayet 104 a pinwheel death star?
As it happens, Wolf-Rayet 104’s orientation is such that the pinwheel looks face-on to us. That adds to its beauty, but it also concerned astronomers. Why? It meant the rotational poles of the two stars might be aimed right toward us. Astronomers expect that one or both of the stars will likely explode in a supernova at some point in the future. That explosion could be powerful enough to produce a gamma-ray burst (GRB). And if that pole on the star was indeed oriented toward us, then the gamma-ray burst would come right toward our solar system, endangering life on Earth.
But based on the new study, however, it appears that’s not be the case. Hill explained:
Our view of the pinwheel dust spiral from Earth absolutely looks face-on (spinning in the plane of the sky), and it seemed like a pretty safe assumption that the two stars are orbiting the same way. When I started this project, I thought the main focus would be the colliding winds and a face-on orbit was a given. Instead, I found something very unexpected. The orbit is tilted at least 30 or 40 degrees out of the plane of the sky.
Another surprising mystery
That 30 to 40 degrees is a healthy margin, meaning any gamma-ray burst would most likely miss us. But why is the dust spiral so tilted relative to the orbits of the stars? That is another mystery researchers will now have to solve. As Hill surmised:
This is such a great example of how, with astronomy, we often begin a study and the universe surprises us with mysteries we didn’t expect. We may answer some questions but create more. In the end, that is sometimes how we learn more about physics and the universe we live in. In this case, WR 104 is not done surprising us yet!
Bottom line: A new study from the Keck Observatory confirms two massive stars in the pinwheel death star won’t send a gamma-ray burst toward Earth after all.
View larger. | Artist’s concept of the Wolf-Rayet 104 pinwheel star system. A new study confirms 2 massive stars are orbiting each other, producing a giant spiral composed of hydrocarbon dust. The study also shows the poles of the stars are not oriented directly toward us as 1st thought, so there is little to no danger of a gamma-ray burst from them hitting Earth, if one of the stars explodes in a supernova. Image via W. M. Keck Observatory/ Adam Makarenko.
Wolf-Rayet 104 is a star system where two massive stars orbit each other. A huge spiral of dust circles around the stars, making it a rare pinwheel star system.
The pinwheel faces right toward us, so astronomers thought the poles of the stars did also. This could present a danger to Earth. Why? If one of the stars exploded in a supernova, it could send a powerful gamma-ray burst directly toward our solar system.
But that isn’t likely to happen, new research from the Keck Observatory shows. The stars’ poles are tilted so much that any gamma-ray burst coming from them would miss us.
Meet Wolf-Rayet 104, the ‘pinwheel death star’
Wolf-Rayet 104 is a famous, rare type of star system known as a pinwheel star. Discovered in 1999, astronomers suspected it consists of two massive stars orbiting each other. As the stars orbit, their stellar winds collide, producing huge amounts of dust. The dust rotates in a giant pinwheel shape. Astronomers using the W. M. Keck Observatory in Hawaii said on March 18, 2025, that they have now confirmed the pair of stars. In addition, they also determined there is little to no danger of Wolf-Rayet 104 emitting a dangerous gamma-ray burst directly toward Earth, as astronomers had previously thought could happen. So the pinwheel death star will seemingly spare us from extinction. Phew!
Astronomer Grant Hill at the Keck Observatory is the author of the latest peer-reviewed research paper. He originally published it in the Monthly Notices of the Royal Astronomical Society on September 19, 2024. Keck issued the new press release on March 18, 2025.
Astronomers discovered Wolf-Rayet 104 back in 1999. It is a rare pinwheel star system due to the huge spiral formation of dust circling a pair of stars. Scientists now suspect it’s actually a triple system, with a third much more distant star connected by gravity. But the pinwheel effect is created by the two main stars. The first of the two is a Wolf-Rayet star. Those stars are hot, bright and massive. Its stellar wind, similar to our sun’s solar wind, is rich in carbon. The other star, an OB star, is even more massive, and its solar wind is mostly hydrogen.
The stellar winds are huge streams of charged particles, or plasmas, flowing out from each star. As the two stars orbit each other, their stellar winds collide, forming hydrocarbon dust. That dust rotates in a giant pinwheel shape around the stars, and it glows brightly in infrared.
Is Wolf-Rayet 104 a pinwheel death star?
As it happens, Wolf-Rayet 104’s orientation is such that the pinwheel looks face-on to us. That adds to its beauty, but it also concerned astronomers. Why? It meant the rotational poles of the two stars might be aimed right toward us. Astronomers expect that one or both of the stars will likely explode in a supernova at some point in the future. That explosion could be powerful enough to produce a gamma-ray burst (GRB). And if that pole on the star was indeed oriented toward us, then the gamma-ray burst would come right toward our solar system, endangering life on Earth.
But based on the new study, however, it appears that’s not be the case. Hill explained:
Our view of the pinwheel dust spiral from Earth absolutely looks face-on (spinning in the plane of the sky), and it seemed like a pretty safe assumption that the two stars are orbiting the same way. When I started this project, I thought the main focus would be the colliding winds and a face-on orbit was a given. Instead, I found something very unexpected. The orbit is tilted at least 30 or 40 degrees out of the plane of the sky.
Another surprising mystery
That 30 to 40 degrees is a healthy margin, meaning any gamma-ray burst would most likely miss us. But why is the dust spiral so tilted relative to the orbits of the stars? That is another mystery researchers will now have to solve. As Hill surmised:
This is such a great example of how, with astronomy, we often begin a study and the universe surprises us with mysteries we didn’t expect. We may answer some questions but create more. In the end, that is sometimes how we learn more about physics and the universe we live in. In this case, WR 104 is not done surprising us yet!
Bottom line: A new study from the Keck Observatory confirms two massive stars in the pinwheel death star won’t send a gamma-ray burst toward Earth after all.
View larger. | This is the Webb space telescope’s view of the 4 young, colorful giant exoplanets in the HR 8799 system, 130 light-years away. The atmospheres of all 4 planets are rich in carbon dioxide. This suggests that they formed much like Jupiter and Saturn, by slowly building solid cores that attract gas from within a planet-forming disk, or protoplanetary disk. Image via NASA/ ESA/ CSA/ STScI/ Laurent Pueyo (STScI)/ William Balmer (JHU)/ Marshall Perrin (STScI).
Taking direct images of exoplanets is difficult, due to their great distances and dimness. Astronomers have only photographed a small number of exoplanets so far.
NASA’s Webb space telescope has obtained new images of five young, giant planets in the HR 8799 and 51 Eridani planetary systems. They look like bright dots in various colors.
All the planets have carbon dioxide-rich atmospheres. This suggests they formed in a manner similar to Jupiter and Saturn in our own solar system.
See colorful giant exoplanets in new Webb images
It’s difficult for astronomers to take direct images of planets orbiting distant stars, or exoplanets. Even the largest exoplanets present a challenge because of how much fainter they are than their host stars. Now, NASA’s Webb space telescope has obtained new direct images of not just one but two planetary systems, HR 8799 and 51 Eridani. Between them, Webb imaged five young giant planets, scientists said on March 17, 2025. Webb also confirmed that the atmospheres of all five planets are rich in carbon dioxide.
The researchers published the peer-reviewed details about the new images and other data in The Astrophysical Journal on March 17, 2025.
5 colorful giant exoplanets in 2 planetary systems
Webb imaged the five planets in two different planetary systems. It used its NIRCam (Near-Infrared Camera) coronagraph, which blocks light from bright stars, to reveal the hidden planets. The planets appear as bright dots in blue, green and red.
The first system, HR 8799, has four known planets and is 130 light-years from Earth. The second system, 51 Eridani, is 97 light-years away and has one young giant planet.
HR 8799 is still young compared to our own solar system, only about 30 million years old. Our solar system, on the other hand, is 4.6 billion years old. This means the planets are still forming and are hot. As a result, they release a lot of infrared radiation, which Webb can analyze.
Rémi Soummer, director of STScI’s Russell B. Makidon Optics Lab and former lead for Webb’s coronagraph instrument, said:
We knew Webb could measure colors of the outer planets in directly imaged systems. We have been waiting for 10 years to confirm that our finely tuned operations of the telescope would also allow us to access the inner planets. Now the results are in and we can do interesting science with it.
Carbon dioxide-rich atmospheres
By using NIRCam and other instruments, Webb analyzed the planets’ atmospheres. It looked for infrared light emitted in wavelengths that are absorbed by specific gases. This can tell the astronomers what the atmospheres are composed of.
Webb found that all five planets have atmospheres rich in carbon dioxide. The atmospheres also contain more heavy elements overall than scientists had previously thought.
View larger. | The Webb space telescope’s view of the young giant planet in the 51 Eridani system, 97 light-years away. Its atmosphere is also rich in carbon dioxide. Image via NASA/ ESA/ CSA/ STScI/ Laurent Pueyo (STScI)/ William Balmer (JHU)/ Marshall Perrin (STScI).
How did the planets form?
The results suggest that the planets formed in a manner similar to Jupiter and Saturn in our solar system, in a process called core accretion. They are gradually building solid cores that then attract more gas from the original planet-forming disk, or protoplanetary disk. That disk is the swirling cloud of gas and dust that planets are born in around stars. Lead author William Balmer, at Johns Hopkins University in Baltimore, Maryland, said:
By spotting these strong carbon dioxide features, we have shown there is a sizable fraction of heavier elements, like carbon, oxygen and iron, in these planets’ atmospheres. Given what we know about the star they orbit, that likely indicates they formed via core accretion, which is an exciting conclusion for planets that we can directly see.
Giant planets can also form through disk instability, when particles of gas rapidly coalesce into massive objects (the young planets) from a cooling disk of material around a new-born star. But in the case of HR 8799 and 51 Eridani, it seems the planets formed through core accretion.
View larger. | Graph showing the spectrum of planet HR 8799 e. It displays the amounts of near-infrared light detected from the planet by Webb at different wavelengths, revealing carbon dioxide and carbon monoxide. Image via NASA/ ESA/ CSA/ STScI/ Joseph Olmsted (STScI).
Understanding our own solar system
Knowing more about how other planetary systems form can also help scientists better understand how our own solar system came to be. Balmer said:
Our hope with this kind of research is to understand our own solar system, life and ourselves in the comparison to other exoplanetary systems, so we can contextualize our existence. We want to take pictures of other solar systems and see how they’re similar or different when compared to ours. From there, we can try to get a sense of how weird our solar system really is, or how normal.
The astronomers are planning additional observations of HR 8799 and 51 Eridani. It’s possible that some of the observed planets might actually be brown dwarfs, but only more observations can confirm that, or not. Brown dwarfs are unusual objects, kind of halfway between the smallest stars and the largest planets. They don’t have enough mass to become fully ignited stars. As co-author Laurent Pueyo, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, noted:
We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach. How common is this for planets we can directly image? We don’t know yet, but we’re proposing more Webb observations to answer that question.
Bottom line: NASA’s Webb space telescope has obtained stunning new images of five young and colorful giant exoplanets. All of them have carbon dioxide-rich atmospheres.
View larger. | This is the Webb space telescope’s view of the 4 young, colorful giant exoplanets in the HR 8799 system, 130 light-years away. The atmospheres of all 4 planets are rich in carbon dioxide. This suggests that they formed much like Jupiter and Saturn, by slowly building solid cores that attract gas from within a planet-forming disk, or protoplanetary disk. Image via NASA/ ESA/ CSA/ STScI/ Laurent Pueyo (STScI)/ William Balmer (JHU)/ Marshall Perrin (STScI).
Taking direct images of exoplanets is difficult, due to their great distances and dimness. Astronomers have only photographed a small number of exoplanets so far.
NASA’s Webb space telescope has obtained new images of five young, giant planets in the HR 8799 and 51 Eridani planetary systems. They look like bright dots in various colors.
All the planets have carbon dioxide-rich atmospheres. This suggests they formed in a manner similar to Jupiter and Saturn in our own solar system.
See colorful giant exoplanets in new Webb images
It’s difficult for astronomers to take direct images of planets orbiting distant stars, or exoplanets. Even the largest exoplanets present a challenge because of how much fainter they are than their host stars. Now, NASA’s Webb space telescope has obtained new direct images of not just one but two planetary systems, HR 8799 and 51 Eridani. Between them, Webb imaged five young giant planets, scientists said on March 17, 2025. Webb also confirmed that the atmospheres of all five planets are rich in carbon dioxide.
The researchers published the peer-reviewed details about the new images and other data in The Astrophysical Journal on March 17, 2025.
5 colorful giant exoplanets in 2 planetary systems
Webb imaged the five planets in two different planetary systems. It used its NIRCam (Near-Infrared Camera) coronagraph, which blocks light from bright stars, to reveal the hidden planets. The planets appear as bright dots in blue, green and red.
The first system, HR 8799, has four known planets and is 130 light-years from Earth. The second system, 51 Eridani, is 97 light-years away and has one young giant planet.
HR 8799 is still young compared to our own solar system, only about 30 million years old. Our solar system, on the other hand, is 4.6 billion years old. This means the planets are still forming and are hot. As a result, they release a lot of infrared radiation, which Webb can analyze.
Rémi Soummer, director of STScI’s Russell B. Makidon Optics Lab and former lead for Webb’s coronagraph instrument, said:
We knew Webb could measure colors of the outer planets in directly imaged systems. We have been waiting for 10 years to confirm that our finely tuned operations of the telescope would also allow us to access the inner planets. Now the results are in and we can do interesting science with it.
Carbon dioxide-rich atmospheres
By using NIRCam and other instruments, Webb analyzed the planets’ atmospheres. It looked for infrared light emitted in wavelengths that are absorbed by specific gases. This can tell the astronomers what the atmospheres are composed of.
Webb found that all five planets have atmospheres rich in carbon dioxide. The atmospheres also contain more heavy elements overall than scientists had previously thought.
View larger. | The Webb space telescope’s view of the young giant planet in the 51 Eridani system, 97 light-years away. Its atmosphere is also rich in carbon dioxide. Image via NASA/ ESA/ CSA/ STScI/ Laurent Pueyo (STScI)/ William Balmer (JHU)/ Marshall Perrin (STScI).
How did the planets form?
The results suggest that the planets formed in a manner similar to Jupiter and Saturn in our solar system, in a process called core accretion. They are gradually building solid cores that then attract more gas from the original planet-forming disk, or protoplanetary disk. That disk is the swirling cloud of gas and dust that planets are born in around stars. Lead author William Balmer, at Johns Hopkins University in Baltimore, Maryland, said:
By spotting these strong carbon dioxide features, we have shown there is a sizable fraction of heavier elements, like carbon, oxygen and iron, in these planets’ atmospheres. Given what we know about the star they orbit, that likely indicates they formed via core accretion, which is an exciting conclusion for planets that we can directly see.
Giant planets can also form through disk instability, when particles of gas rapidly coalesce into massive objects (the young planets) from a cooling disk of material around a new-born star. But in the case of HR 8799 and 51 Eridani, it seems the planets formed through core accretion.
View larger. | Graph showing the spectrum of planet HR 8799 e. It displays the amounts of near-infrared light detected from the planet by Webb at different wavelengths, revealing carbon dioxide and carbon monoxide. Image via NASA/ ESA/ CSA/ STScI/ Joseph Olmsted (STScI).
Understanding our own solar system
Knowing more about how other planetary systems form can also help scientists better understand how our own solar system came to be. Balmer said:
Our hope with this kind of research is to understand our own solar system, life and ourselves in the comparison to other exoplanetary systems, so we can contextualize our existence. We want to take pictures of other solar systems and see how they’re similar or different when compared to ours. From there, we can try to get a sense of how weird our solar system really is, or how normal.
The astronomers are planning additional observations of HR 8799 and 51 Eridani. It’s possible that some of the observed planets might actually be brown dwarfs, but only more observations can confirm that, or not. Brown dwarfs are unusual objects, kind of halfway between the smallest stars and the largest planets. They don’t have enough mass to become fully ignited stars. As co-author Laurent Pueyo, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, noted:
We have other lines of evidence that hint at these four HR 8799 planets forming using this bottom-up approach. How common is this for planets we can directly image? We don’t know yet, but we’re proposing more Webb observations to answer that question.
Bottom line: NASA’s Webb space telescope has obtained stunning new images of five young and colorful giant exoplanets. All of them have carbon dioxide-rich atmospheres.
A dust storm like this one also goes by the name haboob. But what causes the powerful winds that create dust storms, blizzards and more? Image via NOAA.
The world is a windy place. From dust storms to blizzards, hurricanes and tornadoes, powerful winds are at the source of most of our violent storms.
Air moves from regions of high pressure to low pressure. The greater the difference in pressure, the faster the winds will move.
Earth’s rotation causes these winds to spiral around areas of high and low pressure. Air blows clockwise around high pressure and counterclockwise around low pressure.
Windstorms can seem like they come out of nowhere, hitting with a sudden blast. They might be hundreds of miles long, stretching over several states, or just in your neighborhood. But they all have one thing in common: a change in air pressure.
Just like air rushing out of your car tire when the valve is open, air in the atmosphere is forced from areas of high pressure to areas of low pressure. The stronger the difference in pressure, the stronger the winds that will ultimately result.
Other forces related to the Earth’s rotation, friction and gravity can also alter the speed and direction of winds. But it all starts with this change in pressure over a distance. Or what meteorologists like me call a pressure gradient.
On this forecast for March 18, 2025, from the National Oceanic and Atmospheric Administration, ‘L’ represents low-pressure systems. The shaded area over New Mexico and West Texas represents strong winds and low humidity that combine to raise the risk of wildfires.Image via NOAA Weather Prediction Center.
So how do we get pressure gradients?
Strong pressure gradients ultimately owe their existence to the simple fact that the Earth is round and rotates.
Because the Earth is round, the sun is more directly overhead during the day at the equator than at the poles. This means more energy reaches the surface of the Earth near the equator. And that causes the lower part of the atmosphere, where weather occurs, to be both warmer and have higher pressure on average than the poles.
Nature doesn’t like imbalances. As a result of this temperature difference, strong winds develop at high altitudes over mid-latitude locations, like the continental U.S. This is the jet stream. And even though it’s several miles up in the atmosphere, it has a big impact on the winds we feel at the surface.
Wind speed and direction in the upper atmosphere on March 14, 2025, show waves in the jet stream. Downstream of a trough in this wave, winds diverge and low pressure can form near the surface. Image via NCAR.
Powerful winds from high pressure to low pressure
Because Earth rotates, these upper-altitude winds blow from west to east. Waves in the jet stream – a consequence of Earth’s rotation and variations in the surface land, terrain and oceans – can cause air to diverge, or spread out, at certain points. As the air spreads out, the number of air molecules in a column decreases, ultimately reducing the air pressure at Earth’s surface.
The pressure can drop quite dramatically over a few days or even just a few hours, leading to the birth of a low-pressure system. This is what meteorologists call an extratropical cyclone.
In between these low-pressure and high-pressure systems is a strong change in pressure over a distance: a pressure gradient. And that pressure gradient leads to strong winds. Earth’s rotation causes these winds to spiral around areas of high and low pressure. These highs and lows are like large circular mixers, with air blowing clockwise around high pressure and counterclockwise around low pressure. This flow pattern blows warm air northward toward the poles east of lows and cool air southward toward the equator west of lows.
As the waves in the jet stream migrate from west to east, so do the surface lows and highs, and with them, the corridors of strong winds.
A map illustrates lines of surface pressure, called isobars, with areas of high and low pressure marked for March 14, 2025. Winds are strongest when isobars are packed most closely together. Image via Plymouth State University (CC BY-NC-SA 4.0).
Whipping up dust storms and spreading fires
That’s what the U.S. experienced in March 2025 when a strong extratropical cyclone caused winds stretching thousands of miles that whipped up dust storms and spread wildfires. It even caused tornadoes and blizzards in the central and southern U.S.
The jet stream over the U.S. is strongest and often the most “wavy” in the springtime. That’s when the south-to-north difference in temperature is often the strongest.
Winds associated with large-scale pressure systems can become quite strong in areas where there is limited friction at the ground. For example, this happens in the flat, less forested terrain of the Great Plains. One of the biggest risks is dust storms in arid regions of West Texas or eastern New Mexico, exacerbated by drought in these areas.
When the ground and vegetation are dry and the air has low relative humidity, high winds can also spread wildfires out of control.
Even more intense winds can occur when the pressure gradient interacts with terrain. Winds can sometimes rush faster downslope, as happens in the Rockies or with the Santa Ana winds that fueled devastating wildfires in the Los Angeles area in January.
Violent tornadoes and storms
Of course, winds can become even stronger and more violent on local scales associated with thunderstorms.
When thunderstorms form, hail and precipitation in them can cause the air to rapidly fall in a downdraft. This creates very high pressure under these storms. That pressure forces the air to spread out horizontally when it reaches the ground. Meteorologists call these straight line winds. And the process that forms them is a downburst. Large thunderstorms or chains of them moving across a region can cause large swaths of strong wind over 60 mph (about 100 kph), called a derecho.
The powerful winds of a tornado
Finally, some of nature’s strongest winds occur inside tornadoes. They form when the winds surrounding a thunderstorm change speed and direction with height. This can cause part of the storm to rotate. And that sets off a chain of events that may lead to a tornado and winds as strong as 300 mph (about 500 kph) in the most violent tornadoes.
How a tornado forms. Source: NOAA.
Tornado winds are also associated with an intense pressure gradient. The pressure inside the center of a tornado is often very low and varies considerably over a very small distance.
It’s no coincidence that localized violent winds from thunderstorm downbursts and tornadoes often occur amid large-scale windstorms. Extratropical cyclones often draw warm, moist air northward on strong winds from the south. And this is a key ingredient for thunderstorms. Storms also become more severe and may produce tornadoes when the jet stream is in close proximity to these low-pressure centers. In the winter and early spring, cold air funneling south on the northwest side of strong extratropical cyclones can even lead to blizzards.
So, the same wave in the jet stream can lead to strong winds, blowing dust and fire danger in one region, while simultaneously triggering a tornado outbreak and a blizzard in other regions.
Bottom line: The strong, powerful winds of dust storms, blizzards, tornadoes and more are the result of air seeking to stabilize between high pressure and low pressure regions.
A dust storm like this one also goes by the name haboob. But what causes the powerful winds that create dust storms, blizzards and more? Image via NOAA.
The world is a windy place. From dust storms to blizzards, hurricanes and tornadoes, powerful winds are at the source of most of our violent storms.
Air moves from regions of high pressure to low pressure. The greater the difference in pressure, the faster the winds will move.
Earth’s rotation causes these winds to spiral around areas of high and low pressure. Air blows clockwise around high pressure and counterclockwise around low pressure.
Windstorms can seem like they come out of nowhere, hitting with a sudden blast. They might be hundreds of miles long, stretching over several states, or just in your neighborhood. But they all have one thing in common: a change in air pressure.
Just like air rushing out of your car tire when the valve is open, air in the atmosphere is forced from areas of high pressure to areas of low pressure. The stronger the difference in pressure, the stronger the winds that will ultimately result.
Other forces related to the Earth’s rotation, friction and gravity can also alter the speed and direction of winds. But it all starts with this change in pressure over a distance. Or what meteorologists like me call a pressure gradient.
On this forecast for March 18, 2025, from the National Oceanic and Atmospheric Administration, ‘L’ represents low-pressure systems. The shaded area over New Mexico and West Texas represents strong winds and low humidity that combine to raise the risk of wildfires.Image via NOAA Weather Prediction Center.
So how do we get pressure gradients?
Strong pressure gradients ultimately owe their existence to the simple fact that the Earth is round and rotates.
Because the Earth is round, the sun is more directly overhead during the day at the equator than at the poles. This means more energy reaches the surface of the Earth near the equator. And that causes the lower part of the atmosphere, where weather occurs, to be both warmer and have higher pressure on average than the poles.
Nature doesn’t like imbalances. As a result of this temperature difference, strong winds develop at high altitudes over mid-latitude locations, like the continental U.S. This is the jet stream. And even though it’s several miles up in the atmosphere, it has a big impact on the winds we feel at the surface.
Wind speed and direction in the upper atmosphere on March 14, 2025, show waves in the jet stream. Downstream of a trough in this wave, winds diverge and low pressure can form near the surface. Image via NCAR.
Powerful winds from high pressure to low pressure
Because Earth rotates, these upper-altitude winds blow from west to east. Waves in the jet stream – a consequence of Earth’s rotation and variations in the surface land, terrain and oceans – can cause air to diverge, or spread out, at certain points. As the air spreads out, the number of air molecules in a column decreases, ultimately reducing the air pressure at Earth’s surface.
The pressure can drop quite dramatically over a few days or even just a few hours, leading to the birth of a low-pressure system. This is what meteorologists call an extratropical cyclone.
In between these low-pressure and high-pressure systems is a strong change in pressure over a distance: a pressure gradient. And that pressure gradient leads to strong winds. Earth’s rotation causes these winds to spiral around areas of high and low pressure. These highs and lows are like large circular mixers, with air blowing clockwise around high pressure and counterclockwise around low pressure. This flow pattern blows warm air northward toward the poles east of lows and cool air southward toward the equator west of lows.
As the waves in the jet stream migrate from west to east, so do the surface lows and highs, and with them, the corridors of strong winds.
A map illustrates lines of surface pressure, called isobars, with areas of high and low pressure marked for March 14, 2025. Winds are strongest when isobars are packed most closely together. Image via Plymouth State University (CC BY-NC-SA 4.0).
Whipping up dust storms and spreading fires
That’s what the U.S. experienced in March 2025 when a strong extratropical cyclone caused winds stretching thousands of miles that whipped up dust storms and spread wildfires. It even caused tornadoes and blizzards in the central and southern U.S.
The jet stream over the U.S. is strongest and often the most “wavy” in the springtime. That’s when the south-to-north difference in temperature is often the strongest.
Winds associated with large-scale pressure systems can become quite strong in areas where there is limited friction at the ground. For example, this happens in the flat, less forested terrain of the Great Plains. One of the biggest risks is dust storms in arid regions of West Texas or eastern New Mexico, exacerbated by drought in these areas.
When the ground and vegetation are dry and the air has low relative humidity, high winds can also spread wildfires out of control.
Even more intense winds can occur when the pressure gradient interacts with terrain. Winds can sometimes rush faster downslope, as happens in the Rockies or with the Santa Ana winds that fueled devastating wildfires in the Los Angeles area in January.
Violent tornadoes and storms
Of course, winds can become even stronger and more violent on local scales associated with thunderstorms.
When thunderstorms form, hail and precipitation in them can cause the air to rapidly fall in a downdraft. This creates very high pressure under these storms. That pressure forces the air to spread out horizontally when it reaches the ground. Meteorologists call these straight line winds. And the process that forms them is a downburst. Large thunderstorms or chains of them moving across a region can cause large swaths of strong wind over 60 mph (about 100 kph), called a derecho.
The powerful winds of a tornado
Finally, some of nature’s strongest winds occur inside tornadoes. They form when the winds surrounding a thunderstorm change speed and direction with height. This can cause part of the storm to rotate. And that sets off a chain of events that may lead to a tornado and winds as strong as 300 mph (about 500 kph) in the most violent tornadoes.
How a tornado forms. Source: NOAA.
Tornado winds are also associated with an intense pressure gradient. The pressure inside the center of a tornado is often very low and varies considerably over a very small distance.
It’s no coincidence that localized violent winds from thunderstorm downbursts and tornadoes often occur amid large-scale windstorms. Extratropical cyclones often draw warm, moist air northward on strong winds from the south. And this is a key ingredient for thunderstorms. Storms also become more severe and may produce tornadoes when the jet stream is in close proximity to these low-pressure centers. In the winter and early spring, cold air funneling south on the northwest side of strong extratropical cyclones can even lead to blizzards.
So, the same wave in the jet stream can lead to strong winds, blowing dust and fire danger in one region, while simultaneously triggering a tornado outbreak and a blizzard in other regions.
Bottom line: The strong, powerful winds of dust storms, blizzards, tornadoes and more are the result of air seeking to stabilize between high pressure and low pressure regions.
The Spring Triangle is an asterism of the 3 bright stars Arcturus, Spica and Regulus at its corners. All 3 stars are in different constellations. Image via EarthSky.
The Spring Triangle heralds warmer weather
Around the time of the March equinox, a trio of wide-spread stars rises in the east after dark. The Spring Triangle announces the slide into shorter nights and warmer weather for the Northern Hemisphere. Regulus in Leo the Lion is the first to rise above the horizon, having risen before the sun has even set. It’s followed by Arcturus in Boötes the Herdsman. And, just a bit later, Spica in Virgo the Maiden joins the group. These three bright stars create a narrow pyramid stretching up from the horizon.
The Spring Triangle is entirely above the horizon before midnight in March. And by early April, its three stars are visible by mid-evening (midway between sundown and midnight).
Once you come to know it, when you see the Spring Triangle stars above the houses across the street, you can almost feel the warm springtime air.
The Spring Triangle is an asterism
Like the sky’s other seasonal shapes (for instance, the Summer Triangle and Winter Circle or Hexagon), the Spring Triangle isn’t a constellation. It’s not one of the 88 regions of the sky officially recognized as constellations by the International Astronomical Union.
Instead, it’s an asterism, an unofficial but recognizable pattern of stars that can be in one constellation or in multiple constellations. Asterisms are what many of us would pick out as constellations, if we didn’t know any constellations. That’s because they’re often the sky’s most recognizable patterns.
Let’s look at how to find these stars so we can watch them move across the night sky.
Leo the Lion’s brightest star is Regulus. It’s the dot at the bottom of the backward question mark known as the Sickle. Chart via EarthSky.
Regulus
As soon as it’s dark around the March equinox, look for a bright yellowish star twinkling above the eastern horizon. That’s Regulus, and it’s easy to confirm if you’ve spotted the right star. If the star you’re targeting marks the period in a backward question mark pattern of stars, you’ve got it. This question mark shape is another asterism known as the Sickle in Leo. The curve of the question mark traces the head of the lion and Regulus is the Lion’s heart.
When we look at Regulus, we only see one star, but it’s actually a four-star system. From about 79 light-years away, the light from the four stars makes one point of light in the night sky. The brightest star in this system is a yellow supergiant about four times the size of our sun.
Arcturus and its constellation Boötes the Herdsman. Boötes has the shape of a kite. Arcturus is at the point where you’d attach a tail. You can see it on spring evenings in the Northern Hemisphere. Chart via EarthSky.
Arcturus
Next up is Arcturus, the brightest star of the three in the Spring Triangle. For those at northerly latitudes, Arcturus is the second-brightest star visible on the sky’s dome, after Sirius, which is currently in the southwestern sky. (Those at more southerly latitudes, like the southern U.S., can see the sky’s actual second-brightest star, Canopus, in the south.) Arcturus is a gorgeous old red giant about 37 light-years away. Billions of years in the future, when the sun has burnt up its own hydrogen fuel supply, it will turn into a star like the type Arcturus is now.
The constellation Virgo the Maiden is easy to find using the Big Dipper and arcing to Arcturus in Boötes, then speeding on down toward Spica, Virgo’s brightest star. Image via EarthSky.
Spica
If Arcturus has risen, Spica is not far behind. Look for Spica lower in the sky than Arcturus – and father toward the south, or right – of the others. From a distance of 250 light-years away, Spica appears to us on Earth to be a lone bluish-white star in a quiet region of the sky. But Spica consists of two stars and maybe more. The pair are both larger and hotter than our sun, and they’re separated by only 11 million miles (less than 18 million km). They orbit their common center of gravity in only four days.
A triangle inside the triangle
If you can spot the Spring Triangle, you may notice there’s a second triangle inside the larger triangle. The smaller triangle excludes Regulus but includes yellowish Denebola, a double star about 36 light-years away that marks the Lion’s tail. Denebola is the second brightest in Leo. To see this second triangle, see the chart below.
Some stargazers speak of the Spring Triangle as including Denebola instead of Regulus. Image via EarthSky.
The Spring Triangle is less attention-grabbing than the Winter Circle (or Hexagon) and the Summer Triangle. If you’re having trouble finding it, there’s another way. Use the Big Dipper for extra help.
Finding the Spring Triangle
Find the Spring Triangle using the Big Dipper as a guide. Image via EarthSky.
Toward the north, look for the Big Dipper, called the Plough in the United Kingdom. This time of year, by mid-evening it’s ascending in the northeast. If you draw a line from the two stars at the end of the Dipper’s bowl or blade – Dubhe and Merak – and extend it toward the south, you’ll reach Regulus.
Then, follow the curve of the Dipper’s handle away from the bowl to arc to Arcturus and continue the line downward to speed on down to Spica.
Surprisingly enough, the Spring Triangle is bigger than its more famous summertime cousin, and it’s almost as big across as the Winter Hexagon. Yet it’s not one of the best-known star patterns.
Once you’ve found the Spring Triangle, you’ll enjoy it year after year. Maybe because it appears as spring arrives, this pattern seems full of optimism for good things to come!
Bottom Line: Look for a sign of the changing seasons in the heavens as the Spring Triangle, made up of the bright stars Regulus, Arcturus and Spica, rises above the horizon in the east over the next couple of months.
The Spring Triangle is an asterism of the 3 bright stars Arcturus, Spica and Regulus at its corners. All 3 stars are in different constellations. Image via EarthSky.
The Spring Triangle heralds warmer weather
Around the time of the March equinox, a trio of wide-spread stars rises in the east after dark. The Spring Triangle announces the slide into shorter nights and warmer weather for the Northern Hemisphere. Regulus in Leo the Lion is the first to rise above the horizon, having risen before the sun has even set. It’s followed by Arcturus in Boötes the Herdsman. And, just a bit later, Spica in Virgo the Maiden joins the group. These three bright stars create a narrow pyramid stretching up from the horizon.
The Spring Triangle is entirely above the horizon before midnight in March. And by early April, its three stars are visible by mid-evening (midway between sundown and midnight).
Once you come to know it, when you see the Spring Triangle stars above the houses across the street, you can almost feel the warm springtime air.
The Spring Triangle is an asterism
Like the sky’s other seasonal shapes (for instance, the Summer Triangle and Winter Circle or Hexagon), the Spring Triangle isn’t a constellation. It’s not one of the 88 regions of the sky officially recognized as constellations by the International Astronomical Union.
Instead, it’s an asterism, an unofficial but recognizable pattern of stars that can be in one constellation or in multiple constellations. Asterisms are what many of us would pick out as constellations, if we didn’t know any constellations. That’s because they’re often the sky’s most recognizable patterns.
Let’s look at how to find these stars so we can watch them move across the night sky.
Leo the Lion’s brightest star is Regulus. It’s the dot at the bottom of the backward question mark known as the Sickle. Chart via EarthSky.
Regulus
As soon as it’s dark around the March equinox, look for a bright yellowish star twinkling above the eastern horizon. That’s Regulus, and it’s easy to confirm if you’ve spotted the right star. If the star you’re targeting marks the period in a backward question mark pattern of stars, you’ve got it. This question mark shape is another asterism known as the Sickle in Leo. The curve of the question mark traces the head of the lion and Regulus is the Lion’s heart.
When we look at Regulus, we only see one star, but it’s actually a four-star system. From about 79 light-years away, the light from the four stars makes one point of light in the night sky. The brightest star in this system is a yellow supergiant about four times the size of our sun.
Arcturus and its constellation Boötes the Herdsman. Boötes has the shape of a kite. Arcturus is at the point where you’d attach a tail. You can see it on spring evenings in the Northern Hemisphere. Chart via EarthSky.
Arcturus
Next up is Arcturus, the brightest star of the three in the Spring Triangle. For those at northerly latitudes, Arcturus is the second-brightest star visible on the sky’s dome, after Sirius, which is currently in the southwestern sky. (Those at more southerly latitudes, like the southern U.S., can see the sky’s actual second-brightest star, Canopus, in the south.) Arcturus is a gorgeous old red giant about 37 light-years away. Billions of years in the future, when the sun has burnt up its own hydrogen fuel supply, it will turn into a star like the type Arcturus is now.
The constellation Virgo the Maiden is easy to find using the Big Dipper and arcing to Arcturus in Boötes, then speeding on down toward Spica, Virgo’s brightest star. Image via EarthSky.
Spica
If Arcturus has risen, Spica is not far behind. Look for Spica lower in the sky than Arcturus – and father toward the south, or right – of the others. From a distance of 250 light-years away, Spica appears to us on Earth to be a lone bluish-white star in a quiet region of the sky. But Spica consists of two stars and maybe more. The pair are both larger and hotter than our sun, and they’re separated by only 11 million miles (less than 18 million km). They orbit their common center of gravity in only four days.
A triangle inside the triangle
If you can spot the Spring Triangle, you may notice there’s a second triangle inside the larger triangle. The smaller triangle excludes Regulus but includes yellowish Denebola, a double star about 36 light-years away that marks the Lion’s tail. Denebola is the second brightest in Leo. To see this second triangle, see the chart below.
Some stargazers speak of the Spring Triangle as including Denebola instead of Regulus. Image via EarthSky.
The Spring Triangle is less attention-grabbing than the Winter Circle (or Hexagon) and the Summer Triangle. If you’re having trouble finding it, there’s another way. Use the Big Dipper for extra help.
Finding the Spring Triangle
Find the Spring Triangle using the Big Dipper as a guide. Image via EarthSky.
Toward the north, look for the Big Dipper, called the Plough in the United Kingdom. This time of year, by mid-evening it’s ascending in the northeast. If you draw a line from the two stars at the end of the Dipper’s bowl or blade – Dubhe and Merak – and extend it toward the south, you’ll reach Regulus.
Then, follow the curve of the Dipper’s handle away from the bowl to arc to Arcturus and continue the line downward to speed on down to Spica.
Surprisingly enough, the Spring Triangle is bigger than its more famous summertime cousin, and it’s almost as big across as the Winter Hexagon. Yet it’s not one of the best-known star patterns.
Once you’ve found the Spring Triangle, you’ll enjoy it year after year. Maybe because it appears as spring arrives, this pattern seems full of optimism for good things to come!
Bottom Line: Look for a sign of the changing seasons in the heavens as the Spring Triangle, made up of the bright stars Regulus, Arcturus and Spica, rises above the horizon in the east over the next couple of months.
Watch a video about how iguanas floated 1/5 of the way around the world to colonize Fiji. Thumbnail image via Bjørn Christian Tørrissen/ Wikipedia (CC BY-SA 4.0)
For many years, scientists have wondered where the iguanas that inhabit the remote and isolated islands of Fiji and Tonga came from. Finally, a team of researchers from the University of California, Berkeley, and the University of San Francisco (USF) said on March 17, 2025, they have an answer. These reptiles likely arrived on the islands by rafting from western North America. This means the iguanas traveled 5,000 miles (8,000 km) on natural rafts across the Pacific Ocean.
To solve the mystery, the researchers analyzed the DNA of more than 200 iguana specimens from museums around the world. They also discovered that the iguanas arrived on the islands about 34 million years ago, either immediately after the islands’ formation, or shortly afterward. The scientists published their study in the peer-reviewed journal Proceedings of the National Academy of Sciences on March 17, 2025.
Simon Scarpetta, the study’s lead author, is a herpetologist and paleontologist, former postdoctoral fellow at UC Berkeley, and current assistant professor in the USF Department of Environmental Sciences.
Fiji and Tonga iguanas broke a record
Iguanas are fascinating animals: They can change color, detach their tails, have a third eye on top of their heads, know how to swim and can dive for 30 minutes. But traveling 5,000 miles (8,000 km) from the west coast of North America to these distant islands is a big deal.
The four species that inhabit the islands of Fiji and Tonga have earned the well-deserved record for the longest known transoceanic dispersal of any non-human terrestrial vertebrate. These iguanas belong to the genus Brachylophus.
Although iguanas commonly float on natural rafts made of fallen trees and plants – and transport themselves using this system – making such a long journey seemed impossible. Jimmy McGuire, co-author of the study and professor of integrative biology and herpetology curator at the Museum of Vertebrate Zoology, said:
That they reached Fiji directly from North America seems crazy.
There are 45 species of Iguanidae that live in the Caribbean and the tropical, subtropical and desert regions of North, Central and South America. Therefore, scientists looked for the origin of the Brachylophus genus in nearer locations. Central and South America seemed more likely options than North America.
This is a male Fiji crested iguana. Image via Michael Howard/ Wikipedia (CC BY 2.0).
The mysterious origin of Brachylophus iguanas
Seeing iguanas floating on rafts in the Caribbean is a common sight. In fact, this is what happened centuries ago, when they embarked on a 600-mile (970-km) journey from Central America to colonize the Galapagos Islands.
Scientists hypothesized that, if this had occurred previously, the iguanas could have continued their journey further to reach Fiji and Tonga from the western Pacific. Researchers also proposed the idea that they could have arrived from tropical South America, via Antarctica or Australia. However, there is no genetic or fossil evidence to support these hypotheses.
According to McGuire:
When you don’t really know where Brachylophus fits at the base of the tree, then where they came from can also be almost anywhere. So it was much easier to imagine that Brachylophus originated from South America, since we already have marine and land iguanas in the Galapagos that almost certainly dispersed to the islands from the mainland.
This is a Fiji banded iguana at the Vienna Zoo in Austria. Image via Robert F. Tobler/ Wikipedia (CC BY-SA 4.0).
Their origin confirmed!
Previous genetic analyses of some iguanid lizard genes were inconclusive about the relationship of Fiji and Tonga iguanas to the rest. A few years ago, during his postdoctoral studies, lead author Simon Scarpetta began a detailed investigation of all Iguania genera with the goal of clarifying the group’s family tree. McGuire explained that:
Different relationships have been inferred in these various analyses, none with particularly strong support. So there was still this uncertainty about where Brachylophus really fits within the iguanid phylogeny. Simon’s data really nailed this thing.
Scarpetta compiled DNA from genomic sequences of more than 4,000 genes and from tissues of more than 200 iguana specimens found in museum collections around the world. When comparing these data, one result stood out clearly: Fiji and Tonga iguanas are closely related to iguanas of the genus Dipsosaurus.
The most widespread of this genus is the North American desert iguana, Dipsosaurus dorsalis, adapted to the scorching heat of the deserts of the southwestern United States and northern Mexico. Scarpetta stated that:
Iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, so my thought process is, if there had to be any group of vertebrate or any group of lizard that really could make an 8,000 kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one.
This is a male Brachylophus bulabula at the Berlin Aquarium in Germany. Image via JSutton93/ Wikipedia (CC BY-SA 4.0).
The origin of the islands and their colonization
In addition to demonstrating that Brachylophus iguanas did indeed arrive from North America, the scientists also established that they reached Fiji and Tonga around 34 million years ago. They rejected alternative models involving colonization from adjacent lands because they didn’t correspond with this period of time.
In fact, biologists had previously proposed that Fijian and Tongan iguanas could have descended from an older, more widespread lineage in the Pacific (now extinct). However, the dates did not match.
This exhaustive analysis also explains when the genetic divergence of Brachylophus iguanas from their closest relatives, the North American desert iguanas, Dipsosaurus, occurred. The study suggests that Brachylophus iguanas may have even colonized the volcanic islands of Fiji and Tonga as soon as land emerged (34 million years ago) or shortly after their formation, thus diverging from Dipsosaurus iguanas. According to Scarpetta:
We found that the Fiji iguanas are most closely related to the North American desert iguanas, something that hadn’t been figured out before, and that the lineage of Fiji iguanas split from their sister lineage relatively recently, much closer to 30 million years ago, either post-dating or at about the same time that there was volcanic activity that could have produced land.
This is a female Gau iguana. Image via Mark Fraser/ Wikipedia (public domain).
How did they get to the islands?
Despite being very resilient creatures, it’s still surprising how they were able to undertake this adventure. Dispersal over water is the main way newly formed islands are populated with plants and animals.
And this is quite impressive. Let’s imagine the situation … A modern-day sailor using the wind to reach Fiji from California would need about a month to get there. Can you imagine how long it would take the iguanas floating on a raft?
Fortunately, iguanas are accustomed to going long periods of time without food or water. On the other hand, the rafts they traveled on were likely made of fallen trees and other plants. Fortunately, iguanas are herbivores, and the raft itself would have provided them with food.
The dispersal of animals often leads to the evolution of new species and entirely new ecosystems. Other islands besides Fiji and Tonga may have also hosted iguanas, but volcanic islands tend to disappear as easily as they appear. Evidence of other Pacific Island iguanas, if they existed, has likely been lost. So, Fiji’s iguanas are an outlier, lying alone in the middle of the Pacific.
Unfortunately, all four species from Fiji and Tonga are listed as critically endangered. This is primarily due to habitat loss and exploitation by smugglers who fuel the exotic pet trade.
A Fijian crested iguana on at the Taronga Zoo in Australia. Image via Pelagic/ Wikipedia (CC BY-SA 4.0).
Bottom line: Iguanas are incredible reptiles that can live without food or water for long periods of time. This allowed them to travel 5,000 miles from North America to Fiji and Tonga and conquer the islands.
Watch a video about how iguanas floated 1/5 of the way around the world to colonize Fiji. Thumbnail image via Bjørn Christian Tørrissen/ Wikipedia (CC BY-SA 4.0)
For many years, scientists have wondered where the iguanas that inhabit the remote and isolated islands of Fiji and Tonga came from. Finally, a team of researchers from the University of California, Berkeley, and the University of San Francisco (USF) said on March 17, 2025, they have an answer. These reptiles likely arrived on the islands by rafting from western North America. This means the iguanas traveled 5,000 miles (8,000 km) on natural rafts across the Pacific Ocean.
To solve the mystery, the researchers analyzed the DNA of more than 200 iguana specimens from museums around the world. They also discovered that the iguanas arrived on the islands about 34 million years ago, either immediately after the islands’ formation, or shortly afterward. The scientists published their study in the peer-reviewed journal Proceedings of the National Academy of Sciences on March 17, 2025.
Simon Scarpetta, the study’s lead author, is a herpetologist and paleontologist, former postdoctoral fellow at UC Berkeley, and current assistant professor in the USF Department of Environmental Sciences.
Fiji and Tonga iguanas broke a record
Iguanas are fascinating animals: They can change color, detach their tails, have a third eye on top of their heads, know how to swim and can dive for 30 minutes. But traveling 5,000 miles (8,000 km) from the west coast of North America to these distant islands is a big deal.
The four species that inhabit the islands of Fiji and Tonga have earned the well-deserved record for the longest known transoceanic dispersal of any non-human terrestrial vertebrate. These iguanas belong to the genus Brachylophus.
Although iguanas commonly float on natural rafts made of fallen trees and plants – and transport themselves using this system – making such a long journey seemed impossible. Jimmy McGuire, co-author of the study and professor of integrative biology and herpetology curator at the Museum of Vertebrate Zoology, said:
That they reached Fiji directly from North America seems crazy.
There are 45 species of Iguanidae that live in the Caribbean and the tropical, subtropical and desert regions of North, Central and South America. Therefore, scientists looked for the origin of the Brachylophus genus in nearer locations. Central and South America seemed more likely options than North America.
This is a male Fiji crested iguana. Image via Michael Howard/ Wikipedia (CC BY 2.0).
The mysterious origin of Brachylophus iguanas
Seeing iguanas floating on rafts in the Caribbean is a common sight. In fact, this is what happened centuries ago, when they embarked on a 600-mile (970-km) journey from Central America to colonize the Galapagos Islands.
Scientists hypothesized that, if this had occurred previously, the iguanas could have continued their journey further to reach Fiji and Tonga from the western Pacific. Researchers also proposed the idea that they could have arrived from tropical South America, via Antarctica or Australia. However, there is no genetic or fossil evidence to support these hypotheses.
According to McGuire:
When you don’t really know where Brachylophus fits at the base of the tree, then where they came from can also be almost anywhere. So it was much easier to imagine that Brachylophus originated from South America, since we already have marine and land iguanas in the Galapagos that almost certainly dispersed to the islands from the mainland.
This is a Fiji banded iguana at the Vienna Zoo in Austria. Image via Robert F. Tobler/ Wikipedia (CC BY-SA 4.0).
Their origin confirmed!
Previous genetic analyses of some iguanid lizard genes were inconclusive about the relationship of Fiji and Tonga iguanas to the rest. A few years ago, during his postdoctoral studies, lead author Simon Scarpetta began a detailed investigation of all Iguania genera with the goal of clarifying the group’s family tree. McGuire explained that:
Different relationships have been inferred in these various analyses, none with particularly strong support. So there was still this uncertainty about where Brachylophus really fits within the iguanid phylogeny. Simon’s data really nailed this thing.
Scarpetta compiled DNA from genomic sequences of more than 4,000 genes and from tissues of more than 200 iguana specimens found in museum collections around the world. When comparing these data, one result stood out clearly: Fiji and Tonga iguanas are closely related to iguanas of the genus Dipsosaurus.
The most widespread of this genus is the North American desert iguana, Dipsosaurus dorsalis, adapted to the scorching heat of the deserts of the southwestern United States and northern Mexico. Scarpetta stated that:
Iguanas and desert iguanas, in particular, are resistant to starvation and dehydration, so my thought process is, if there had to be any group of vertebrate or any group of lizard that really could make an 8,000 kilometer journey across the Pacific on a mass of vegetation, a desert iguana-like ancestor would be the one.
This is a male Brachylophus bulabula at the Berlin Aquarium in Germany. Image via JSutton93/ Wikipedia (CC BY-SA 4.0).
The origin of the islands and their colonization
In addition to demonstrating that Brachylophus iguanas did indeed arrive from North America, the scientists also established that they reached Fiji and Tonga around 34 million years ago. They rejected alternative models involving colonization from adjacent lands because they didn’t correspond with this period of time.
In fact, biologists had previously proposed that Fijian and Tongan iguanas could have descended from an older, more widespread lineage in the Pacific (now extinct). However, the dates did not match.
This exhaustive analysis also explains when the genetic divergence of Brachylophus iguanas from their closest relatives, the North American desert iguanas, Dipsosaurus, occurred. The study suggests that Brachylophus iguanas may have even colonized the volcanic islands of Fiji and Tonga as soon as land emerged (34 million years ago) or shortly after their formation, thus diverging from Dipsosaurus iguanas. According to Scarpetta:
We found that the Fiji iguanas are most closely related to the North American desert iguanas, something that hadn’t been figured out before, and that the lineage of Fiji iguanas split from their sister lineage relatively recently, much closer to 30 million years ago, either post-dating or at about the same time that there was volcanic activity that could have produced land.
This is a female Gau iguana. Image via Mark Fraser/ Wikipedia (public domain).
How did they get to the islands?
Despite being very resilient creatures, it’s still surprising how they were able to undertake this adventure. Dispersal over water is the main way newly formed islands are populated with plants and animals.
And this is quite impressive. Let’s imagine the situation … A modern-day sailor using the wind to reach Fiji from California would need about a month to get there. Can you imagine how long it would take the iguanas floating on a raft?
Fortunately, iguanas are accustomed to going long periods of time without food or water. On the other hand, the rafts they traveled on were likely made of fallen trees and other plants. Fortunately, iguanas are herbivores, and the raft itself would have provided them with food.
The dispersal of animals often leads to the evolution of new species and entirely new ecosystems. Other islands besides Fiji and Tonga may have also hosted iguanas, but volcanic islands tend to disappear as easily as they appear. Evidence of other Pacific Island iguanas, if they existed, has likely been lost. So, Fiji’s iguanas are an outlier, lying alone in the middle of the Pacific.
Unfortunately, all four species from Fiji and Tonga are listed as critically endangered. This is primarily due to habitat loss and exploitation by smugglers who fuel the exotic pet trade.
A Fijian crested iguana on at the Taronga Zoo in Australia. Image via Pelagic/ Wikipedia (CC BY-SA 4.0).
Bottom line: Iguanas are incredible reptiles that can live without food or water for long periods of time. This allowed them to travel 5,000 miles from North America to Fiji and Tonga and conquer the islands.
View larger. | Artist’s concept of an Earth-like planet orbiting a white dwarf star. A new study says white dwarfs could provide perfect conditions for life on nearby worlds. Image via Adam Makarenko/ W. M. Keck Observatory.
White dwarfs could host life-supporting planets
Does a star have to be alive – that is, shining from within, burning thermonuclear fuel at its core – in order to sustain life? Scientists assumed that white dwarfs – the dense remnants of dead stars – would likely be unable to support life on nearby planets. They assumed these continuously cooling stellar corpses would be unable to provide a consistent source of energy. But on March 18, 2025, researchers at the Florida Institute of Technology said they’d investigated whether white dwarfs could power three processes that have helped life to thrive on Earth. And they found these dead stars could provide the perfect conditions for life on an Earth-like planet for nearly 7 billion years.
They published their peer-reviewed results in The Astrophysical Journal Letters on December 12, 2024.
White dwarfs are fading star cores
White dwarfs are the final evolutionary stage for most low-to-moderate-mass stars, including our sun. In fact, some 97% of stars in our Milky Way galaxy are destined to become white dwarfs. When one of these stars eventually starts to run out of hydrogen fuel, it will expand into a bloated red giant, before shedding its outer layers altogether. This will produce a beautiful planetary nebula, with the star’s roughly Earth-sized core at its center. This remnant is what we call a white dwarf.
The expansion into a red giant would in many cases destroy the planets surrounding it. This is likely (although not certainly) what will happen to Earth in some 5 billion years. But studies have found that this fate is far from inevitable. And, sure enough, scientists in recent years have made various detections of planets orbiting white dwarfs.
The bigger obstacle to life orbiting a white dwarf is that these dead stars lack the fuel to perform nuclear fusion. So, although white dwarfs start their lives incredibly hot, over billions of years they leak out their trapped heat. This steady cooling is why scientists have long thought that white dwarfs are unlikely to host habitable planets. The dead stars seem unable to provide the consistent energy life would need to establish itself.
View larger. | The Ring Nebula (M57) in the constellation Lyra shows the final stages of a star like our sun. The white dot in the center of this nebula is a white dwarf. It’s lighting up the receding cloud of gas that once made up the star. The colors identify various elements like hydrogen, helium and oxygen. Image via The Hubble Heritage Team (AURA/ STScI/ NASA).
Measuring habitable zones
But a white dwarf’s heat dissipates over a timescale of billions of years. So the researchers set out to establish how long life on a nearby planet could be sustained before the white dwarf cooled too much.
They constructed a model to simulate how long a planet could remain within a white dwarf’s gradually shrinking “habitable zone”. That is, the region in which the temperature is just right for a planet to sustain liquid water on its surface. And they found that, if positioned perfectly, an Earth-like planet close to a white dwarf could receive enough starlight to maintain liquid water for 7 billion years. Considering Earth is around 4.5 billion years old and began hosting life at least 3.5 billion years ago, 7 billion years would seem more than enough time for life to emerge.
It’s worth noting that, in recent years, scientists have come to realize that the concept of habitable zones might be outdated. We now believe moons like Enceladus and Europa, far beyond our solar system’s Goldilocks zone, have global liquid oceans hidden beneath vast sheets of ice. And these oceans may well be habitable, or even inhabited. But this study focused on the only environment we know to have produced life: a planet like Earth, with abundant liquid water on its surface.
The cooler the star, the smaller the habitable zone. And in the case of a white dwarf, that band of habitability would be constantly moving inward. Image via Kepler mission/ Ames Research Center/ NASA/ Britannica.
Can a white dwarf support life’s key processes?
To get a better understanding of this theoretical planet’s true habitability, the researchers also investigated whether the white dwarf’s energy would be enough to sustain two chemical processes that have helped life thrive on Earth.
The first is photosynthesis, which not only powers much of Earth’s life, but has also made our planet’s biosphere more habitable. And the second is UV-induced abiogenesis, or the generation of life from non-living matter via ultraviolet radiation. The transformation of simple molecules into more complex ones through ultraviolet radiation is seen as a likely origin of life on Earth.
And the researchers found that an ideally placed planet would receive the energy to support photosynthesis and UV-induced abiogenesis for the entirety of its 7-billion-year habitable period. And that, according to study lead Caldon Whyte, is highly rare. He explained:
That isn’t really common around most stars. Something like [our] sun, of course, can provide enough energy, but brown dwarfs and red dwarfs smaller than the sun don’t really provide the energy in [both] the UV and the photosynthesis range.
Far from being unsuited to sustaining alien life, it appears white dwarfs are uniquely suited to the task.
So are white dwarfs the key to future alien searches?
This surprising availability of energy makes planets orbiting close to white dwarfs strong candidates in the search for alien life. This is especially true given the 7 billion years of potential habitability they offer. Such an extended timeframe, the paper points out, raises the possibility of technologically advanced life. So a planet orbiting close to a white dwarf star could be a prime location to search for technosignatures.
The major complication is that we haven’t yet found a planet orbiting close enough to a white dwarf for this level of habitability. The paper acknowledges that a star’s red giant phase would likely engulf a planet in this orbital region. However, that doesn’t mean they don’t exist. Studies have suggested that planets could form again in this zone after the red giant phase, made from the recycled material of destroyed planets.
Our current generation of telescopes struggle to spot small exoplanets very close to their stars, so it’s hard to say how common these kinds of planets are. But if Earth-like planets close to white dwarfs are common, they could be some of the most likely locations to find alien life.
Bottom line: According to a surprising new study, white dwarfs could provide enough energy to sustain life on a nearby Earth-like planet for some 7 billion years.
View larger. | Artist’s concept of an Earth-like planet orbiting a white dwarf star. A new study says white dwarfs could provide perfect conditions for life on nearby worlds. Image via Adam Makarenko/ W. M. Keck Observatory.
White dwarfs could host life-supporting planets
Does a star have to be alive – that is, shining from within, burning thermonuclear fuel at its core – in order to sustain life? Scientists assumed that white dwarfs – the dense remnants of dead stars – would likely be unable to support life on nearby planets. They assumed these continuously cooling stellar corpses would be unable to provide a consistent source of energy. But on March 18, 2025, researchers at the Florida Institute of Technology said they’d investigated whether white dwarfs could power three processes that have helped life to thrive on Earth. And they found these dead stars could provide the perfect conditions for life on an Earth-like planet for nearly 7 billion years.
They published their peer-reviewed results in The Astrophysical Journal Letters on December 12, 2024.
White dwarfs are fading star cores
White dwarfs are the final evolutionary stage for most low-to-moderate-mass stars, including our sun. In fact, some 97% of stars in our Milky Way galaxy are destined to become white dwarfs. When one of these stars eventually starts to run out of hydrogen fuel, it will expand into a bloated red giant, before shedding its outer layers altogether. This will produce a beautiful planetary nebula, with the star’s roughly Earth-sized core at its center. This remnant is what we call a white dwarf.
The expansion into a red giant would in many cases destroy the planets surrounding it. This is likely (although not certainly) what will happen to Earth in some 5 billion years. But studies have found that this fate is far from inevitable. And, sure enough, scientists in recent years have made various detections of planets orbiting white dwarfs.
The bigger obstacle to life orbiting a white dwarf is that these dead stars lack the fuel to perform nuclear fusion. So, although white dwarfs start their lives incredibly hot, over billions of years they leak out their trapped heat. This steady cooling is why scientists have long thought that white dwarfs are unlikely to host habitable planets. The dead stars seem unable to provide the consistent energy life would need to establish itself.
View larger. | The Ring Nebula (M57) in the constellation Lyra shows the final stages of a star like our sun. The white dot in the center of this nebula is a white dwarf. It’s lighting up the receding cloud of gas that once made up the star. The colors identify various elements like hydrogen, helium and oxygen. Image via The Hubble Heritage Team (AURA/ STScI/ NASA).
Measuring habitable zones
But a white dwarf’s heat dissipates over a timescale of billions of years. So the researchers set out to establish how long life on a nearby planet could be sustained before the white dwarf cooled too much.
They constructed a model to simulate how long a planet could remain within a white dwarf’s gradually shrinking “habitable zone”. That is, the region in which the temperature is just right for a planet to sustain liquid water on its surface. And they found that, if positioned perfectly, an Earth-like planet close to a white dwarf could receive enough starlight to maintain liquid water for 7 billion years. Considering Earth is around 4.5 billion years old and began hosting life at least 3.5 billion years ago, 7 billion years would seem more than enough time for life to emerge.
It’s worth noting that, in recent years, scientists have come to realize that the concept of habitable zones might be outdated. We now believe moons like Enceladus and Europa, far beyond our solar system’s Goldilocks zone, have global liquid oceans hidden beneath vast sheets of ice. And these oceans may well be habitable, or even inhabited. But this study focused on the only environment we know to have produced life: a planet like Earth, with abundant liquid water on its surface.
The cooler the star, the smaller the habitable zone. And in the case of a white dwarf, that band of habitability would be constantly moving inward. Image via Kepler mission/ Ames Research Center/ NASA/ Britannica.
Can a white dwarf support life’s key processes?
To get a better understanding of this theoretical planet’s true habitability, the researchers also investigated whether the white dwarf’s energy would be enough to sustain two chemical processes that have helped life thrive on Earth.
The first is photosynthesis, which not only powers much of Earth’s life, but has also made our planet’s biosphere more habitable. And the second is UV-induced abiogenesis, or the generation of life from non-living matter via ultraviolet radiation. The transformation of simple molecules into more complex ones through ultraviolet radiation is seen as a likely origin of life on Earth.
And the researchers found that an ideally placed planet would receive the energy to support photosynthesis and UV-induced abiogenesis for the entirety of its 7-billion-year habitable period. And that, according to study lead Caldon Whyte, is highly rare. He explained:
That isn’t really common around most stars. Something like [our] sun, of course, can provide enough energy, but brown dwarfs and red dwarfs smaller than the sun don’t really provide the energy in [both] the UV and the photosynthesis range.
Far from being unsuited to sustaining alien life, it appears white dwarfs are uniquely suited to the task.
So are white dwarfs the key to future alien searches?
This surprising availability of energy makes planets orbiting close to white dwarfs strong candidates in the search for alien life. This is especially true given the 7 billion years of potential habitability they offer. Such an extended timeframe, the paper points out, raises the possibility of technologically advanced life. So a planet orbiting close to a white dwarf star could be a prime location to search for technosignatures.
The major complication is that we haven’t yet found a planet orbiting close enough to a white dwarf for this level of habitability. The paper acknowledges that a star’s red giant phase would likely engulf a planet in this orbital region. However, that doesn’t mean they don’t exist. Studies have suggested that planets could form again in this zone after the red giant phase, made from the recycled material of destroyed planets.
Our current generation of telescopes struggle to spot small exoplanets very close to their stars, so it’s hard to say how common these kinds of planets are. But if Earth-like planets close to white dwarfs are common, they could be some of the most likely locations to find alien life.
Bottom line: According to a surprising new study, white dwarfs could provide enough energy to sustain life on a nearby Earth-like planet for some 7 billion years.
A galaxy is a vast island of gas, dust and stars in an ocean of space. Typically, galaxies are millions of light-years apart. Galaxies are the building blocks of our universe. Their distribution isn’t random, as one might suppose. Instead, galaxies reside along unimaginably long filaments across the universe, forming a cosmic web of star cities.
View larger. | Have you ever wondered what a galaxy is or how many galaxies are in the universe? Here’s the Webb telescope’s 1st deep field, released in July 2022. This near-infrared image of the galaxy cluster SMACS 0723 contains thousands of galaxies. High-resolution imaging from Webb – combined with a natural effect known as gravitational lensing – made this finely detailed image possible. Image via NASA/ ESA/ CSA/ STScI. Read more about this image.
A galaxy can contain hundreds of billions of stars and be many thousands of light-years across. Our own galaxy, the Milky Way, is around 100,000 light-years in diameter. That’s about 587,900 trillion miles, or nearly a million trillion kilometers.
The three types of galaxies are spiral, elliptical or irregular.
Galaxy sizes vary widely, ranging from very small to unbelievably enormous. Small dwarf galaxies contain about 100 million stars. Giant galaxies contain more than a trillion stars.
Also, there are an estimated two hundred billion galaxies in the universe.
Here is a closeup view of 1 small portion of a Webb image that shows more than 45,000 galaxies. Image via NASA/ ESA/ CSA/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Marcia Rieke (University of Arizona)/ Daniel Eisenstein (CfA)/ Alyssa Pagan (STScI).
The discovery of other galaxies
The famous astronomer Edwin P. Hubble first classified galaxies based on their visual appearance in the late 1920s and 30s. In fact, Hubble’s classification of galaxies remains in use today. Of course, since Hubble’s time, like any effective classification system, it has evolved from ongoing observations. Hubble identified several basic types of galaxies, each containing subtypes.
— Royal Astronomical Society (@RoyalAstroSoc) June 11, 2019
Before Hubble’s study of galaxies, we believed that our galaxy was the only one in the universe. Astronomers thought that the smudges of light they saw through their telescopes were in fact nebulae within our own galaxy. However, Hubble discovered that these nebulae were galaxies. Additionally, it was Hubble who demonstrated, by measuring their velocities, that they lie at vast distances from us.
Galaxies are light-years away
These galaxies lie millions of light-years beyond the Milky Way. The distances are so huge these galaxies appear tiny in all but the largest telescopes. Moreover, Hubble demonstrated that, wherever he looked, galaxies were receding from us in all directions. And the farther away they are, the faster they are receding. Thus, Hubble had discovered that the universe is expanding.
View at EarthSky Community Photos. | Harshwardhan Pathak of India, using a large remote telescope in Chile, captured the galaxy NGC 1232 in the constellation Eridanus on February 1, 2024. Harshwardhan wrote: “NGC 1232, also known as the Eye of God Galaxy, is an intermediate spiral galaxy about 60 million light-years away. German-British astronomer William Herschel discovered it on October 20, 1784.” Thank you, Harshwardhan!
Spiral galaxies
The most common type of galaxy is a spiral galaxy. The Milky Way is a spiral galaxy. Spiral galaxies have majestic, sweeping arms, thousands of light-years long. They contain millions upon millions of stars. Their spiral arms stand out because of bright stars, glowing gas and dust. Spiral galaxies are active with star formation.
Also, spiral galaxies have a bright center, made up of a dense concentration of stars. There are so many stars that from a distance the galaxy’s center looks like a solid ball. This ball of stars is known as the galactic bulge.
Also, there are two types of spiral galaxies. There are regular spirals and barred spirals. If the spiral has bars, they extend off the central bulge. Then, the spiral arms start at the end of the bar.
The 3 most common types of galaxies. The top row shows schematic illustrations, and the bottom row shows actual images of galaxies that fit each of the 3 categories. Image via A. Feild/ STScI/ Hubblesite.
Elliptical and irregular galaxies
Elliptical galaxies are the universe’s largest galaxies. In fact, giant elliptical galaxies can be about 300,000 light-years across. But dwarf elliptical galaxies – the most common elliptical – are only a few thousand light-years across. There are several shapes of elliptical galaxies, ranging from circular to football-shaped.
Overall, 1/3 of all galaxies are elliptical galaxies. Elliptical galaxies contain very little gas and dust compared to a spiral or irregular galaxy. They are no longer actively forming stars. The stars in elliptical galaxies are older stars and contain very few heavier elements.
Irregular-shaped galaxies have all sorts of different shapes but they don’t look like a spiral or elliptical galaxy.
Irregular galaxies can have very little dust or a lot. Plus, they can show active star-forming regions or have little-to-no star formation occurring. They seemed plentiful in the early universe.
View larger. | This Hubble Space Telescope mosaic is of a portion of the immense Coma Berenices galaxy cluster. Be sure to use the view larger link and zoom in to see how much larger the football-shaped elliptical galaxies are, in contrast to the spiral galaxies. Image via NASA/ ESA/ J. Mack (STScI)/ J. Madrid (Australian Telescope National Facility).
Our Milky Way galaxy
The Milky Way, in fact, falls into one of Hubble’s spiral galaxy sub-types. It’s a barred spiral, which means it has a bar of stars protruding out from each side of its center. As the spiral arms sweep out in their graceful and enormous arcs, the ends of the bars are the anchors. This is a recent discovery and it’s unknown how bars form in a galaxy. Our solar system is situated about 2/3 of the way out from the galactic center toward the periphery of the galaxy, embedded in one of these spiral arms.
Another recent discovery is that the disk of the Milky Way is warped, like a long-playing vinyl record left too long in the sun. Exactly why is unknown, but it may be the result of a gravitational encounter with another galaxy early in the Milky Way’s history.
It also appears that all galaxies rotate. For example, the Milky Way takes 226 million years to spin around once. Since its creation, the Earth has traveled 20 times around the galaxy.
Galaxies come in clusters
Galaxies group together in clusters. Our own galaxy is part of what is called the Local Group, and it contains roughly 55 galaxies.
The “glue” that binds stars into galaxies, galaxies into clusters, clusters into superclusters and superclusters into filaments is – of course – gravity. In fact, gravity is the universe’s construction worker, which sculpts all the structures we see in the cosmos.
The Universe is Infinite. However our existence in our current Galaxy Cluster is Finite. Time is also a factor… Our Galaxy Clusters actually expand into the void of space over time. pic.twitter.com/EAOcisPdZn
Most galaxies are flying apart from each other. But those astronomically close to each other will be gravitationally bound to each other. Caught in an inexorable gravitational dance, eventually they merge, passing through each other over millions of years. They eventually form a single, amorphous elliptical galaxy. Gravity shockwaves compress huge clouds of interstellar gas and dust during such mergers, giving rise to new generations of stars.
The Milky Way is caught in such a gravitational embrace with M31, aka the Andromeda galaxy, which is 2 1/2 million light-years distant. Both galaxies are moving toward each other because of gravitational attraction: they will merge in about 6 billion years. However, huge halos of gas surround both galaxies and may extend for millions of light-years. And it was discovered that the halos of the Milky Way and M31 have already started to touch.
Galaxy mergers and companion galaxies
Galaxy mergers are common. The universe is full of examples of galaxies in various stages of merging together, their structures disrupted and distorted by gravity, forming bizarre and beautiful shapes.
Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can only see glimpses of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed the Mice Galaxies because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via NASA/ ESA/ Wikimedia Commons (public domain).
Then, at the lower end of the galactic size scale, there are so-called dwarf galaxies. They consist of a few hundred to up to several billion stars. Their origin is not clear. Typically, they have no clearly defined structure. Astronomers believe they were born in the same way as larger galaxies like the Milky Way, but for whatever reason they stopped growing. Ensnared by the gravity of a larger galaxy, they orbit its periphery. The Milky Way has around 60 dwarf galaxies orbiting it that we know of, although some models predict there should be many more.
The two most famous dwarf galaxies for us earthlings are, of course, the Large and Small Magellanic Clouds, visible to the unaided eye in Earth’s Southern Hemisphere sky.
Eventually, these and other dwarf galaxies will rip apart under the titanic pull of the Milky Way’s gravity. This will leave behind a barely noticeable stream of stars across the sky, slowly dissipating over eons.
The Large Magellanic Cloud spills across the border of Dorado and Mensa. The Small Magellanic Cloud is at lower left. Image via Yuri Beletsky/ LCO/ ESO.
Supermassive black holes lurk in galaxy centers
At the center of most galaxies lurks a supermassive black hole, of millions or even billions of solar masses. For example, TON 618, has a mass 66 billion times that of our sun. The one at the center of our own Milky Way galaxy possesses 4.6 million solar masses.
The origin and evolution of supermassive black holes remains a mystery. A few years ago, astronomers uncovered a surprising fact: in spiral galaxies, the mass of the supermassive black hole has a direct linear relationship with the mass of the galactic bulge. The more mass the black hole has, the more stars there are in the bulge. No one knows exactly what the significance of this relationship may be. However, its existence seems to indicate that the growth of a galaxy’s stellar population is linked to that of its supermassive black hole.
This discovery comes at a time when astronomers are beginning to realize that a supermassive black hole may control the fate of its host galaxy. The copious amount of electromagnetic radiation emitted from the maelstrom of material orbiting the central black hole. This is known as the accretion disk, and the radiation may push away and dissipate the clouds of interstellar hydrogen from which new stars form. This acts as an inhibitor on the galaxy’s ability to give birth to new stars. Ultimately, the activity of supermassive black holes may link to the emergence of life itself. This is an area that is undergoing extensive research.
While astronomers still know very little about exactly how galaxies formed in the first place – we see them in their nascent state only a few hundred million years after the Big Bang – the study of galaxies is an endless voyage of discovery.
We discovered other galaxies exist about a century ago
Around a hundred years ago we realized that other galaxies exist besides our own. Since then, we have learned so much about these grand, majestic star cities. And there is still much to learn.
Bottom line: A galaxy is a vast island of gas, dust and stars in an ocean of space. There are three types of galaxies. Learn about these starry islands in space.
A galaxy is a vast island of gas, dust and stars in an ocean of space. Typically, galaxies are millions of light-years apart. Galaxies are the building blocks of our universe. Their distribution isn’t random, as one might suppose. Instead, galaxies reside along unimaginably long filaments across the universe, forming a cosmic web of star cities.
View larger. | Have you ever wondered what a galaxy is or how many galaxies are in the universe? Here’s the Webb telescope’s 1st deep field, released in July 2022. This near-infrared image of the galaxy cluster SMACS 0723 contains thousands of galaxies. High-resolution imaging from Webb – combined with a natural effect known as gravitational lensing – made this finely detailed image possible. Image via NASA/ ESA/ CSA/ STScI. Read more about this image.
A galaxy can contain hundreds of billions of stars and be many thousands of light-years across. Our own galaxy, the Milky Way, is around 100,000 light-years in diameter. That’s about 587,900 trillion miles, or nearly a million trillion kilometers.
The three types of galaxies are spiral, elliptical or irregular.
Galaxy sizes vary widely, ranging from very small to unbelievably enormous. Small dwarf galaxies contain about 100 million stars. Giant galaxies contain more than a trillion stars.
Also, there are an estimated two hundred billion galaxies in the universe.
Here is a closeup view of 1 small portion of a Webb image that shows more than 45,000 galaxies. Image via NASA/ ESA/ CSA/ Brant Robertson (UC Santa Cruz)/ Ben Johnson (CfA)/ Sandro Tacchella (Cambridge)/ Marcia Rieke (University of Arizona)/ Daniel Eisenstein (CfA)/ Alyssa Pagan (STScI).
The discovery of other galaxies
The famous astronomer Edwin P. Hubble first classified galaxies based on their visual appearance in the late 1920s and 30s. In fact, Hubble’s classification of galaxies remains in use today. Of course, since Hubble’s time, like any effective classification system, it has evolved from ongoing observations. Hubble identified several basic types of galaxies, each containing subtypes.
— Royal Astronomical Society (@RoyalAstroSoc) June 11, 2019
Before Hubble’s study of galaxies, we believed that our galaxy was the only one in the universe. Astronomers thought that the smudges of light they saw through their telescopes were in fact nebulae within our own galaxy. However, Hubble discovered that these nebulae were galaxies. Additionally, it was Hubble who demonstrated, by measuring their velocities, that they lie at vast distances from us.
Galaxies are light-years away
These galaxies lie millions of light-years beyond the Milky Way. The distances are so huge these galaxies appear tiny in all but the largest telescopes. Moreover, Hubble demonstrated that, wherever he looked, galaxies were receding from us in all directions. And the farther away they are, the faster they are receding. Thus, Hubble had discovered that the universe is expanding.
View at EarthSky Community Photos. | Harshwardhan Pathak of India, using a large remote telescope in Chile, captured the galaxy NGC 1232 in the constellation Eridanus on February 1, 2024. Harshwardhan wrote: “NGC 1232, also known as the Eye of God Galaxy, is an intermediate spiral galaxy about 60 million light-years away. German-British astronomer William Herschel discovered it on October 20, 1784.” Thank you, Harshwardhan!
Spiral galaxies
The most common type of galaxy is a spiral galaxy. The Milky Way is a spiral galaxy. Spiral galaxies have majestic, sweeping arms, thousands of light-years long. They contain millions upon millions of stars. Their spiral arms stand out because of bright stars, glowing gas and dust. Spiral galaxies are active with star formation.
Also, spiral galaxies have a bright center, made up of a dense concentration of stars. There are so many stars that from a distance the galaxy’s center looks like a solid ball. This ball of stars is known as the galactic bulge.
Also, there are two types of spiral galaxies. There are regular spirals and barred spirals. If the spiral has bars, they extend off the central bulge. Then, the spiral arms start at the end of the bar.
The 3 most common types of galaxies. The top row shows schematic illustrations, and the bottom row shows actual images of galaxies that fit each of the 3 categories. Image via A. Feild/ STScI/ Hubblesite.
Elliptical and irregular galaxies
Elliptical galaxies are the universe’s largest galaxies. In fact, giant elliptical galaxies can be about 300,000 light-years across. But dwarf elliptical galaxies – the most common elliptical – are only a few thousand light-years across. There are several shapes of elliptical galaxies, ranging from circular to football-shaped.
Overall, 1/3 of all galaxies are elliptical galaxies. Elliptical galaxies contain very little gas and dust compared to a spiral or irregular galaxy. They are no longer actively forming stars. The stars in elliptical galaxies are older stars and contain very few heavier elements.
Irregular-shaped galaxies have all sorts of different shapes but they don’t look like a spiral or elliptical galaxy.
Irregular galaxies can have very little dust or a lot. Plus, they can show active star-forming regions or have little-to-no star formation occurring. They seemed plentiful in the early universe.
View larger. | This Hubble Space Telescope mosaic is of a portion of the immense Coma Berenices galaxy cluster. Be sure to use the view larger link and zoom in to see how much larger the football-shaped elliptical galaxies are, in contrast to the spiral galaxies. Image via NASA/ ESA/ J. Mack (STScI)/ J. Madrid (Australian Telescope National Facility).
Our Milky Way galaxy
The Milky Way, in fact, falls into one of Hubble’s spiral galaxy sub-types. It’s a barred spiral, which means it has a bar of stars protruding out from each side of its center. As the spiral arms sweep out in their graceful and enormous arcs, the ends of the bars are the anchors. This is a recent discovery and it’s unknown how bars form in a galaxy. Our solar system is situated about 2/3 of the way out from the galactic center toward the periphery of the galaxy, embedded in one of these spiral arms.
Another recent discovery is that the disk of the Milky Way is warped, like a long-playing vinyl record left too long in the sun. Exactly why is unknown, but it may be the result of a gravitational encounter with another galaxy early in the Milky Way’s history.
It also appears that all galaxies rotate. For example, the Milky Way takes 226 million years to spin around once. Since its creation, the Earth has traveled 20 times around the galaxy.
Galaxies come in clusters
Galaxies group together in clusters. Our own galaxy is part of what is called the Local Group, and it contains roughly 55 galaxies.
The “glue” that binds stars into galaxies, galaxies into clusters, clusters into superclusters and superclusters into filaments is – of course – gravity. In fact, gravity is the universe’s construction worker, which sculpts all the structures we see in the cosmos.
The Universe is Infinite. However our existence in our current Galaxy Cluster is Finite. Time is also a factor… Our Galaxy Clusters actually expand into the void of space over time. pic.twitter.com/EAOcisPdZn
Most galaxies are flying apart from each other. But those astronomically close to each other will be gravitationally bound to each other. Caught in an inexorable gravitational dance, eventually they merge, passing through each other over millions of years. They eventually form a single, amorphous elliptical galaxy. Gravity shockwaves compress huge clouds of interstellar gas and dust during such mergers, giving rise to new generations of stars.
The Milky Way is caught in such a gravitational embrace with M31, aka the Andromeda galaxy, which is 2 1/2 million light-years distant. Both galaxies are moving toward each other because of gravitational attraction: they will merge in about 6 billion years. However, huge halos of gas surround both galaxies and may extend for millions of light-years. And it was discovered that the halos of the Milky Way and M31 have already started to touch.
Galaxy mergers and companion galaxies
Galaxy mergers are common. The universe is full of examples of galaxies in various stages of merging together, their structures disrupted and distorted by gravity, forming bizarre and beautiful shapes.
Galaxies may take billions of years to fully merge into a single galaxy. As astronomers look outward in space, they can only see glimpses of this long merger process. Located 300 million light-years away in the constellation Coma Berenices, these 2 colliding galaxies have been nicknamed the Mice Galaxies because of the long tails of stars and gas emanating from each galaxy. Otherwise known as NGC 4676, the pair will eventually merge into a single giant galaxy. Image via NASA/ ESA/ Wikimedia Commons (public domain).
Then, at the lower end of the galactic size scale, there are so-called dwarf galaxies. They consist of a few hundred to up to several billion stars. Their origin is not clear. Typically, they have no clearly defined structure. Astronomers believe they were born in the same way as larger galaxies like the Milky Way, but for whatever reason they stopped growing. Ensnared by the gravity of a larger galaxy, they orbit its periphery. The Milky Way has around 60 dwarf galaxies orbiting it that we know of, although some models predict there should be many more.
The two most famous dwarf galaxies for us earthlings are, of course, the Large and Small Magellanic Clouds, visible to the unaided eye in Earth’s Southern Hemisphere sky.
Eventually, these and other dwarf galaxies will rip apart under the titanic pull of the Milky Way’s gravity. This will leave behind a barely noticeable stream of stars across the sky, slowly dissipating over eons.
The Large Magellanic Cloud spills across the border of Dorado and Mensa. The Small Magellanic Cloud is at lower left. Image via Yuri Beletsky/ LCO/ ESO.
Supermassive black holes lurk in galaxy centers
At the center of most galaxies lurks a supermassive black hole, of millions or even billions of solar masses. For example, TON 618, has a mass 66 billion times that of our sun. The one at the center of our own Milky Way galaxy possesses 4.6 million solar masses.
The origin and evolution of supermassive black holes remains a mystery. A few years ago, astronomers uncovered a surprising fact: in spiral galaxies, the mass of the supermassive black hole has a direct linear relationship with the mass of the galactic bulge. The more mass the black hole has, the more stars there are in the bulge. No one knows exactly what the significance of this relationship may be. However, its existence seems to indicate that the growth of a galaxy’s stellar population is linked to that of its supermassive black hole.
This discovery comes at a time when astronomers are beginning to realize that a supermassive black hole may control the fate of its host galaxy. The copious amount of electromagnetic radiation emitted from the maelstrom of material orbiting the central black hole. This is known as the accretion disk, and the radiation may push away and dissipate the clouds of interstellar hydrogen from which new stars form. This acts as an inhibitor on the galaxy’s ability to give birth to new stars. Ultimately, the activity of supermassive black holes may link to the emergence of life itself. This is an area that is undergoing extensive research.
While astronomers still know very little about exactly how galaxies formed in the first place – we see them in their nascent state only a few hundred million years after the Big Bang – the study of galaxies is an endless voyage of discovery.
We discovered other galaxies exist about a century ago
Around a hundred years ago we realized that other galaxies exist besides our own. Since then, we have learned so much about these grand, majestic star cities. And there is still much to learn.
Bottom line: A galaxy is a vast island of gas, dust and stars in an ocean of space. There are three types of galaxies. Learn about these starry islands in space.
