Göran Strand captured this image on September 27, 2019 in the mountain area of Jämtland, Sweden. He wrote:
A night with quite a strong aurora activity. This is a photo I took facing south. You can see the Milky Way behind the clouds stretching over the sky at the top of the image. These low moving clouds were colored green from the northern lights shining in the north. You can see some of the northern lights at the top of the image.
Göran Strand captured this image on September 27, 2019 in the mountain area of Jämtland, Sweden. He wrote:
A night with quite a strong aurora activity. This is a photo I took facing south. You can see the Milky Way behind the clouds stretching over the sky at the top of the image. These low moving clouds were colored green from the northern lights shining in the north. You can see some of the northern lights at the top of the image.
Tonight, look for Arcturus, one of three stars noticeable for flashing in colors in the evening sky at this time of year. You should be able to see it in the west at dusk or nightfall. Once it gets good and dark, and you live at mid-to-far latitudes in the Northern Hemisphere, you can verify that this star is Arcturus by using the Big Dipper asterism.
The arc of the Big Dipper handle extended outward always points to Arcturus.
Notice that Arcturus is an orange-colored star.
Every year at this time, we get questions about three different stars that are flashing different colors. One is Arcturus in the constellation Bootes the Herdsman, shining in the west to northwest after sunset. Another is Capella in the constellation Auriga the Charioteer, which is now in the northeast in mid-evening. And the third is Sirius in the constellation Canis Major the Greater Dog, which is now in the south before dawn.
All three appear to be flashing colors for the same reason … all three of these stars are bright and, at this time of year, noticeably low in the sky as seen from Northern Hemisphere locations. When you see an object low in the sky, you’re seeing it through a greater thickness of atmosphere than when it’s overhead. The atmosphere refracts or splits the stars’ light to cause these stars to flash in the colors of the rainbow.
At mid-northern latitudes, scintillating Arcturus adorns the western evening sky all through October.
If they were located at the same distance from us, you’d see that Arcturus is a much, much larger star than our sun. Image via Windows to the Universe
Bottom line: On October evenings, look for the brilliant star Arcturus in the western sky, flashing in colors. You can be sure you’ve identified this yellow-orange star if the handle of the Big Dipper points to it.
from EarthSky https://ift.tt/2ATi87t
Tonight, look for Arcturus, one of three stars noticeable for flashing in colors in the evening sky at this time of year. You should be able to see it in the west at dusk or nightfall. Once it gets good and dark, and you live at mid-to-far latitudes in the Northern Hemisphere, you can verify that this star is Arcturus by using the Big Dipper asterism.
The arc of the Big Dipper handle extended outward always points to Arcturus.
Notice that Arcturus is an orange-colored star.
Every year at this time, we get questions about three different stars that are flashing different colors. One is Arcturus in the constellation Bootes the Herdsman, shining in the west to northwest after sunset. Another is Capella in the constellation Auriga the Charioteer, which is now in the northeast in mid-evening. And the third is Sirius in the constellation Canis Major the Greater Dog, which is now in the south before dawn.
All three appear to be flashing colors for the same reason … all three of these stars are bright and, at this time of year, noticeably low in the sky as seen from Northern Hemisphere locations. When you see an object low in the sky, you’re seeing it through a greater thickness of atmosphere than when it’s overhead. The atmosphere refracts or splits the stars’ light to cause these stars to flash in the colors of the rainbow.
At mid-northern latitudes, scintillating Arcturus adorns the western evening sky all through October.
If they were located at the same distance from us, you’d see that Arcturus is a much, much larger star than our sun. Image via Windows to the Universe
Bottom line: On October evenings, look for the brilliant star Arcturus in the western sky, flashing in colors. You can be sure you’ve identified this yellow-orange star if the handle of the Big Dipper points to it.
A cool shot of a Taurid fireball, from November 11, 2015, by Bill Allen. Thanks, Bill! By all reports, this shower was amazing in 2015.
For the most part, we count on the Observer’s Handbook to provide us with the peak dates for the year’s major meteor showers. The Observer’s Handbook 2019 lists November 6 (0 hours Universal Time) as the peak time for the 2019 South Taurid meteor shower. We find this prediction re-echoed in Sky & Telescope magazine’s Skygazer’s Almanac 2019 as well as other publications.
Yet two other trusted sources give a different date for the South Taurid peak. The International Meteor Organization (IMO) says the night of October 9-10. The American Meteor Society (AMS) also gives the night of October 9-10, claiming that this shower:
… rarely produces more than five shower members per hour, even at maximum activity.
Astronomer Guy Ottewell, in his 2012 Astronomical Calendar, helps to explain the discrepancy for the peak date of the South Taurid meteor shower. He explained:
Fresh IMO evidence suggests the Southern branch, rather than reaching its maximum in early November as long believed, actually has its peak in October instead.
Whenever this year’s peak may happen, it’s probably safe to assume that the long-lasting South Taurid meteor shower (September 10 to November 20) will display no sharp peak.
The Taurid meteors consist of two streams, the South Taurid and North Taurid meteors. Both streams appear to originate from the constellation Taurus the Bull.
These South Taurid meteors steadily amble along for weeks on end, rarely exhibiting any more than five meteors per hour! So the moon’s phase may play more of a role than the peak date. This year, in 2019, the nearly-full waxing gibbous moon obtrudes on the show on the night of October 9-10, whereas the moon will be a little past its first quarter on the night of November 5-6. The latter date – November 5-6 – may be better, because the moon will set around midnight, providing more moon-free viewing time.
But the new moon comes on October 28, 2019. So for about a week, centered on this date, you’ll have a dark sky for watching these meteors. If you’re a weekend warrior, the weekend starting on Friday, October 25,2019, may be your best bet for watching the Taurid shower.
From what we have been able to gather, the Taurid meteor stream consists of an extremely wide roadway of far-flung debris left behind by Comet 2P/Encke. When Earth travels through this belt of comet debris, bits and pieces of Comet 2P/Encke smash into the Earth’s upper atmosphere to vaporize as rather slow-moving Taurid meteors (28 km/17 miles per second).
Yet, the Taurids are known for having a high percentage of fireballs.
Apparently, the original Taurid stream had been perturbed by Jupiter into two branches: South and North Taurids. The South Taurids, the more prominent of the two, are active from about September 10 to November 20, whereas the North Taurids are active from about October 20 to December 10.
View larger. | South Taurid meteor. Note the Pleiades star cluster above the meteor, and the bright star Aldebaran roughly midway between the Pleiades and the meteor. Image via Flickr user Rocky Raybell.
Peak dates aside, meteor aficionados will be on the lookout as the South and North Taurids simultaneously produce meteors in late October and early November. Higher rates of Taurid fireballs might happen in seven-year cycles, and the last grand fireball display was in 2015.
In short, the Taurid meteors might produce a “swarm” of fireballs in late October and early November, regardless of which date the South Taurid meteor shower peaks!
Bottom line: It’s meteor season! This shower rarely produces more than 5 meteors per hour (although it’s been known to produce fireballs). Now … when do the South Taurids peak, October or November?
from EarthSky https://ift.tt/30Tt4gc
A cool shot of a Taurid fireball, from November 11, 2015, by Bill Allen. Thanks, Bill! By all reports, this shower was amazing in 2015.
For the most part, we count on the Observer’s Handbook to provide us with the peak dates for the year’s major meteor showers. The Observer’s Handbook 2019 lists November 6 (0 hours Universal Time) as the peak time for the 2019 South Taurid meteor shower. We find this prediction re-echoed in Sky & Telescope magazine’s Skygazer’s Almanac 2019 as well as other publications.
Yet two other trusted sources give a different date for the South Taurid peak. The International Meteor Organization (IMO) says the night of October 9-10. The American Meteor Society (AMS) also gives the night of October 9-10, claiming that this shower:
… rarely produces more than five shower members per hour, even at maximum activity.
Astronomer Guy Ottewell, in his 2012 Astronomical Calendar, helps to explain the discrepancy for the peak date of the South Taurid meteor shower. He explained:
Fresh IMO evidence suggests the Southern branch, rather than reaching its maximum in early November as long believed, actually has its peak in October instead.
Whenever this year’s peak may happen, it’s probably safe to assume that the long-lasting South Taurid meteor shower (September 10 to November 20) will display no sharp peak.
The Taurid meteors consist of two streams, the South Taurid and North Taurid meteors. Both streams appear to originate from the constellation Taurus the Bull.
These South Taurid meteors steadily amble along for weeks on end, rarely exhibiting any more than five meteors per hour! So the moon’s phase may play more of a role than the peak date. This year, in 2019, the nearly-full waxing gibbous moon obtrudes on the show on the night of October 9-10, whereas the moon will be a little past its first quarter on the night of November 5-6. The latter date – November 5-6 – may be better, because the moon will set around midnight, providing more moon-free viewing time.
But the new moon comes on October 28, 2019. So for about a week, centered on this date, you’ll have a dark sky for watching these meteors. If you’re a weekend warrior, the weekend starting on Friday, October 25,2019, may be your best bet for watching the Taurid shower.
From what we have been able to gather, the Taurid meteor stream consists of an extremely wide roadway of far-flung debris left behind by Comet 2P/Encke. When Earth travels through this belt of comet debris, bits and pieces of Comet 2P/Encke smash into the Earth’s upper atmosphere to vaporize as rather slow-moving Taurid meteors (28 km/17 miles per second).
Yet, the Taurids are known for having a high percentage of fireballs.
Apparently, the original Taurid stream had been perturbed by Jupiter into two branches: South and North Taurids. The South Taurids, the more prominent of the two, are active from about September 10 to November 20, whereas the North Taurids are active from about October 20 to December 10.
View larger. | South Taurid meteor. Note the Pleiades star cluster above the meteor, and the bright star Aldebaran roughly midway between the Pleiades and the meteor. Image via Flickr user Rocky Raybell.
Peak dates aside, meteor aficionados will be on the lookout as the South and North Taurids simultaneously produce meteors in late October and early November. Higher rates of Taurid fireballs might happen in seven-year cycles, and the last grand fireball display was in 2015.
In short, the Taurid meteors might produce a “swarm” of fireballs in late October and early November, regardless of which date the South Taurid meteor shower peaks!
Bottom line: It’s meteor season! This shower rarely produces more than 5 meteors per hour (although it’s been known to produce fireballs). Now … when do the South Taurids peak, October or November?
Notice the spiral structure here? This isn’t a galaxy; it’s a computer simulation of a newly forming solar system. It’s part of the disk instability model of how planets form, a model that’s been less accepted by astronomers – until now. A new discovery suggests this model may be correct. If so, Jupiter-like worlds may be common around nearby sunlike stars. Image via astronomical theorist Alan Boss/Carnegie Science.
Astronomers have discovered more than 4,000 exoplanets so far, and the number is still going up. Many are gas giant worlds like Jupiter or Saturn in our solar system, but that’s in part selection bias; the more massive exoplanets orbiting closer to their stars are the easiest exoplanets to find. Now, a new study suggests that there may be a large population of still-unseen Jupiter-like exoplanets waiting to be found orbiting nearby sunlike stars. The new results, from theorist Alan Boss at Carnegie Institution for Science, relate in a profound way to astronomers’ understanding of how planets form. These results have been accepted for publication in an upcoming issue of The Astrophysical Journal.
Boss’s new work is supported by a September 27, 2019, paper, published in the peer-reviewed journal Science, reporting on the discovery of a new exoplanet labeled GJ 3512b. This confirmed, massive, Jupiter-like planet orbits a very low-mass red dwarf star. And thus this planet – sometimes called the planet that shouldn’t exist – belies the previously most-popular theory of planetary formation, which had suggested it was impossible for such a massive planet to form around such a small star. From the September 27 paper:
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit … We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories …
It’s the challenge of the “impossible exoplanet” GJ 3512b to the most widely accepted planet-formation model that Boss is now addressing in his new paper.
The new study is supported by, and expands on, the discovery of GJ 3512b, a gas giant that “shouldn’t exist” because current planet formation theory says it is too big for its very small star. Image via The Sun.
Astronomical theorists – people who’ve spent entire careers studying how planets form – have settled on two scenarios for the formation of gas giant planets. One scenario is called core accretion, and the other is called disk instability. In core accretion, planets slowly form through the collisions of increasingly larger material in the debris disk of gas and dust surrounding a young star, such as dust grains, pebbles, boulders, and eventually larger planetesimals. Meanwhile, the competing theory – disk instability – suggests a rapidly triggered process that occurs when the debris disk is massive and cool enough to form spiral arms.
According to the disk instability model of how planets form, clumps of self-gravitating gas and dust then form and contract and coalesce into a baby planet.
Core accretion has been the dominant theory for some time now, but planets like GJ 3512b represent a challenge to it. Boss has long been a proponent of the disk instability theory. With GJ 3512b now discovered and confirmed, Boss more than ever believes disk instability is the correct model for the formation of gas giant planets, and – if so – that there are many more Jupiter-like planets waiting to be found. According to Guillem Anglada-Escudé, a former Carnegie postdoc who worked with Boss on disk instability models, now at the Institute for Space Studies of Catalonia:
It’s a great vindication for the disk instability method and a demonstration how one unusual discovery can swing the pendulum on our understanding of how planets form.
Alan Boss, a theorist and observational astronomer at Carnegie Institution for Science. Image via Carnegie Institution for Science.
Here’s the big problem with core accretion as an explanation for planets like GJ 3512b. According to core accretion, the mass of a debris disk should be proportional to the mass of the young star around which it revolves. When you have a star that’s much smaller than our sun – hosting a planet that should be too big for it – then either the original debris disk was enormous in relation to this star, or core accretion just didn’t work in this planetary system.
In contrast, in the disk instability scenario, hot debris disks start out as very stable. As they gradually cool down, they form spiral arms around the star – yes, spiral arms similar to those in a galaxy – from which dense clumps eventually form planets. And as it turns out, the gas giants resulting from that process are at similar distances from their stars as Jupiter and Saturn are from the sun. As Boss surmised:
My new models show that disk instability can form dense clumps at distances similar to those of the solar system’s giant planets. The exoplanet census is still very much underway, and this work suggests that there are many more gas giants out there waiting to be counted.
If Boss is right, then disk instability for the creation of planets may be more common than thought, and there should be many more Jupiter-like worlds waiting to be discovered around nearby stars. Finding more planets like GJ 3512b would make that scenario even more compelling.
Artist’s concept of exoplanet GJ 504b, a gas giant 57 light-years away. Similar worlds may be common around nearby stars, according to a new study by theorist Alan Boss. Image via Goddard Space Flight Center/S. Wiessinger/Sci-News.
Bottom line: A new study from Carnegie Institution for Science suggests there are many more Jupiter-like gas giant planets orbiting nearby stars, waiting to be found. The study expands on the recent discovery of GJ 3512b, a massive planet that should be too large for its small star, and “shouldn’t even exist” according to the current most-popular theory of how planets form.
Notice the spiral structure here? This isn’t a galaxy; it’s a computer simulation of a newly forming solar system. It’s part of the disk instability model of how planets form, a model that’s been less accepted by astronomers – until now. A new discovery suggests this model may be correct. If so, Jupiter-like worlds may be common around nearby sunlike stars. Image via astronomical theorist Alan Boss/Carnegie Science.
Astronomers have discovered more than 4,000 exoplanets so far, and the number is still going up. Many are gas giant worlds like Jupiter or Saturn in our solar system, but that’s in part selection bias; the more massive exoplanets orbiting closer to their stars are the easiest exoplanets to find. Now, a new study suggests that there may be a large population of still-unseen Jupiter-like exoplanets waiting to be found orbiting nearby sunlike stars. The new results, from theorist Alan Boss at Carnegie Institution for Science, relate in a profound way to astronomers’ understanding of how planets form. These results have been accepted for publication in an upcoming issue of The Astrophysical Journal.
Boss’s new work is supported by a September 27, 2019, paper, published in the peer-reviewed journal Science, reporting on the discovery of a new exoplanet labeled GJ 3512b. This confirmed, massive, Jupiter-like planet orbits a very low-mass red dwarf star. And thus this planet – sometimes called the planet that shouldn’t exist – belies the previously most-popular theory of planetary formation, which had suggested it was impossible for such a massive planet to form around such a small star. From the September 27 paper:
Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit … We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories …
It’s the challenge of the “impossible exoplanet” GJ 3512b to the most widely accepted planet-formation model that Boss is now addressing in his new paper.
The new study is supported by, and expands on, the discovery of GJ 3512b, a gas giant that “shouldn’t exist” because current planet formation theory says it is too big for its very small star. Image via The Sun.
Astronomical theorists – people who’ve spent entire careers studying how planets form – have settled on two scenarios for the formation of gas giant planets. One scenario is called core accretion, and the other is called disk instability. In core accretion, planets slowly form through the collisions of increasingly larger material in the debris disk of gas and dust surrounding a young star, such as dust grains, pebbles, boulders, and eventually larger planetesimals. Meanwhile, the competing theory – disk instability – suggests a rapidly triggered process that occurs when the debris disk is massive and cool enough to form spiral arms.
According to the disk instability model of how planets form, clumps of self-gravitating gas and dust then form and contract and coalesce into a baby planet.
Core accretion has been the dominant theory for some time now, but planets like GJ 3512b represent a challenge to it. Boss has long been a proponent of the disk instability theory. With GJ 3512b now discovered and confirmed, Boss more than ever believes disk instability is the correct model for the formation of gas giant planets, and – if so – that there are many more Jupiter-like planets waiting to be found. According to Guillem Anglada-Escudé, a former Carnegie postdoc who worked with Boss on disk instability models, now at the Institute for Space Studies of Catalonia:
It’s a great vindication for the disk instability method and a demonstration how one unusual discovery can swing the pendulum on our understanding of how planets form.
Alan Boss, a theorist and observational astronomer at Carnegie Institution for Science. Image via Carnegie Institution for Science.
Here’s the big problem with core accretion as an explanation for planets like GJ 3512b. According to core accretion, the mass of a debris disk should be proportional to the mass of the young star around which it revolves. When you have a star that’s much smaller than our sun – hosting a planet that should be too big for it – then either the original debris disk was enormous in relation to this star, or core accretion just didn’t work in this planetary system.
In contrast, in the disk instability scenario, hot debris disks start out as very stable. As they gradually cool down, they form spiral arms around the star – yes, spiral arms similar to those in a galaxy – from which dense clumps eventually form planets. And as it turns out, the gas giants resulting from that process are at similar distances from their stars as Jupiter and Saturn are from the sun. As Boss surmised:
My new models show that disk instability can form dense clumps at distances similar to those of the solar system’s giant planets. The exoplanet census is still very much underway, and this work suggests that there are many more gas giants out there waiting to be counted.
If Boss is right, then disk instability for the creation of planets may be more common than thought, and there should be many more Jupiter-like worlds waiting to be discovered around nearby stars. Finding more planets like GJ 3512b would make that scenario even more compelling.
Artist’s concept of exoplanet GJ 504b, a gas giant 57 light-years away. Similar worlds may be common around nearby stars, according to a new study by theorist Alan Boss. Image via Goddard Space Flight Center/S. Wiessinger/Sci-News.
Bottom line: A new study from Carnegie Institution for Science suggests there are many more Jupiter-like gas giant planets orbiting nearby stars, waiting to be found. The study expands on the recent discovery of GJ 3512b, a massive planet that should be too large for its small star, and “shouldn’t even exist” according to the current most-popular theory of how planets form.
Have you been missing the brightest planet Venus? I know I have. It’s been gone from our sky for several months, passing behind the sun from Earth’s point of view. Venus’ superior conjunction was August 14; that was when it was most directly behind the sun from us, traveling on the far side of the solar system, lost in the sun’s glare to all earthly observers. Photographers using telephoto lenses began to spot Venus again in early to mid-September. It’s been visible from Earth’s Southern Hemisphere since late September, because, from there, the ecliptic, or sun’s path, is angled more perpendicularly to the evening horizon at this time of year. We in this hemisphere will begin to see Venus again, low in the west very shortly after sunset, this month. Can’t wait? This video tracks a telescopic view of Venus, from when it reappears in the evening sky in September-October 2019, all the way to May 2020. EarthSky friend Larry Koehn of the great website shadowandsubstance.com made this animation. He wrote at Vimeo:
Venus will stay with us after sunset from September-October 2019, through May 2020. Venus will reach inferior conjunction [passing between us and the sun] on June 3 of 2020, and, thus, return to the morning sky in June.
Mercury will appear three times above the horizon during this time period with the first appearance occurring this October.
Jupiter and Saturn can be seen approaching the southwestern horizon from October through January. You will note that Jupiter and Saturn will both travel in a straight line. Mercury and Venus will not!
Venus will exhibit various phases of illumination, as the months progress, much like the moon, with Venus reaching less than 10 percent illumination (crescent phase) in May 2020.
All animations are set for exactly 30 minutes after sunset.
Thank you, Larry!
By the way, why will Venus begin to show phases toward the end of its evening apparition in 2020? And why does it get so much bigger, as seen through a telescope? The phases are because Venus is an inner planet. As it draws near to passing between us and the sun on June 3, it’ll turn its lighted face (its day side) increasingly away from us; hence, we’ll see a waning Venus. Its size in our sky is about the distance between us and Venus. That distance will be decreasing, obviously, as Venus comes near to passing between us and the sun. Thus Venus will be at its largest as viewed through telescopes – and clearly brighter when viewed with the eye alone – shortly before it disappears into the sunset glare in late May.
Okay, so when will you see Venus again with the eye alone? We can’t say for sure. It depends on your sky conditions and on where you are on the globe. But all of us should be able to see Venus by late October, when the waxing crescent moon will sweep near it in the sky, as shown on the chart below:
Have you been missing the brightest planet Venus? I know I have. It’s been gone from our sky for several months, passing behind the sun from Earth’s point of view. Venus’ superior conjunction was August 14; that was when it was most directly behind the sun from us, traveling on the far side of the solar system, lost in the sun’s glare to all earthly observers. Photographers using telephoto lenses began to spot Venus again in early to mid-September. It’s been visible from Earth’s Southern Hemisphere since late September, because, from there, the ecliptic, or sun’s path, is angled more perpendicularly to the evening horizon at this time of year. We in this hemisphere will begin to see Venus again, low in the west very shortly after sunset, this month. Can’t wait? This video tracks a telescopic view of Venus, from when it reappears in the evening sky in September-October 2019, all the way to May 2020. EarthSky friend Larry Koehn of the great website shadowandsubstance.com made this animation. He wrote at Vimeo:
Venus will stay with us after sunset from September-October 2019, through May 2020. Venus will reach inferior conjunction [passing between us and the sun] on June 3 of 2020, and, thus, return to the morning sky in June.
Mercury will appear three times above the horizon during this time period with the first appearance occurring this October.
Jupiter and Saturn can be seen approaching the southwestern horizon from October through January. You will note that Jupiter and Saturn will both travel in a straight line. Mercury and Venus will not!
Venus will exhibit various phases of illumination, as the months progress, much like the moon, with Venus reaching less than 10 percent illumination (crescent phase) in May 2020.
All animations are set for exactly 30 minutes after sunset.
Thank you, Larry!
By the way, why will Venus begin to show phases toward the end of its evening apparition in 2020? And why does it get so much bigger, as seen through a telescope? The phases are because Venus is an inner planet. As it draws near to passing between us and the sun on June 3, it’ll turn its lighted face (its day side) increasingly away from us; hence, we’ll see a waning Venus. Its size in our sky is about the distance between us and Venus. That distance will be decreasing, obviously, as Venus comes near to passing between us and the sun. Thus Venus will be at its largest as viewed through telescopes – and clearly brighter when viewed with the eye alone – shortly before it disappears into the sunset glare in late May.
Okay, so when will you see Venus again with the eye alone? We can’t say for sure. It depends on your sky conditions and on where you are on the globe. But all of us should be able to see Venus by late October, when the waxing crescent moon will sweep near it in the sky, as shown on the chart below:
After counting all the normal, luminous matter in the obvious places of the universe – galaxies, clusters of galaxies and the intergalactic medium – about half of it is still missing. So not only is 85% of the matter in the universe made up of an unknown, invisible substance dubbed “dark matter”, we can’t even find all the small amount of normal matter that should be there.
This is known as the “missing baryons” problem. Baryons are particles that emit or absorb light, like protons, neutrons or electrons, which make up the matter we see around us. The baryons unaccounted for are thought to be hidden in filamentary structures permeating the entire universe, also known as “the cosmic web.”
But this structure is elusive and so far we have only seen glimpses of it. Now a new study, published in Science, offers a better view that will enable us to help map what it looks like.
The cosmic web provides the scaffolding of the large scale structure in the universe, predicted by the “standard cosmological model.” Cosmologists believe there is a dark cosmic web, made of dark matter, and a luminous cosmic web, made of mostly hydrogen gas. In fact, it is believed that 60% of the hydrogen created during the Big Bang resides in these filaments.
The web of gas filaments is also known as the “warm-hot intergalactic medium” (WHIM), because it is roughly as hot as the sun’s interior. Galaxies are likely to form at the intersection of two or more such filaments, where the matter is densest, with the filaments connecting all galaxy clusters in the universe.
So far, we haven’t been able to detect dark matter. This is because it does not emit or absorb light so it cannot be observed with usual telescopes. The cosmic web filaments are also very hard to find as they are very diffuse and they do not emit sufficient light to be detected.
Since the original prediction, there has been an intense search for the cosmic web, using a variety of methods.
One of these relies on bright objects that happen to lie in the background along the same line of sight as a gas filament. The hydrogen atoms in the filaments can absorb light at a specific wavelength in the ultraviolet. This can be detected as absorption lines in the light from the background object, when broken down into a spectrum by wavelength.
This method has been applied using quasars, which are very bright massive objects at large distances, and even with background galaxies.
Galaxies lighting up the web
The new study has managed to detect the gas in an entirely new way which allows two dimensional imaging of the cosmic web, rather than relying on the random location of a bright source behind the gas cloud used in absorption studies.
The object they studied, catchily named SSA22, is a proto-cluster, meaning it is a cluster of galaxies in its infancy. It is much farther away than previous measured bits of the cosmic web – its light travelled about 12 billion years to reach us. This means we are looking back in time to the early stages of the universe, allowing scientists to probe how the filaments first assembled.
Map showing the gas filaments (blue) running from the top to the bottom of the image. The white dots are very active star forming galaxies which are being fed by the filaments. Image iva Hideki Umehata.
A few years ago, a number of extremely bright, star-forming galaxies called “sub-millimeter galaxies” were detected near its center. This new study has found 16 such galaxies and eight powerful X-ray sources, a rare over-density of such objects at this early epoch. The objects provide copious amount of ionizing radiation to all of the hydrogen gas of the filaments, which makes it emit light that we can detect – a technique that holds much more promise than absorption.
Another mystery that this study helps to solve is the formation of sub-millimeter galaxies. The most widely agreed on explanation is that they form as a result of two normal galaxies merging, hence forming a massive galaxy with double the amount of light.
However, computer simulations show that these galaxies can grow from the cold gas pouring in from the neighboring cosmic web. This scenario is confirmed by this new study.
Detailed map
The new study paves the way for a more systematic, two-dimensional mapping of gas filaments that can tell us about their motions in space.
Future studies help further map the hidden cosmic web. In addition to looking at galaxy clusters full of bright objects, we can also trace the web’s emission in radio or X-ray wavelengths. However, the X-ray traces much hotter gas than the bulk of the WHIM. The proposed Athena X-ray observatory will provide a full picture of the hot filaments around the clusters of galaxies in the nearby universe.
Another proposed mission for beyond 2050 is to use the cosmic microwave background – the light left over from the Big Bang – as a “background light” and look for fine imprints left in it by the cosmic web.
All these tools will reveal the entire structure of the cosmic web and provide us with a definitive census of the matter in the universe.
What’s more, we know that baryons settle in the dark matter filaments of the universe to make their own filaments, like foam over an existing wave. This means that detailed maps of the gas filaments can help us trace the more hidden dark matter structure and, ultimately, help us understand its mysterious nature.
After counting all the normal, luminous matter in the obvious places of the universe – galaxies, clusters of galaxies and the intergalactic medium – about half of it is still missing. So not only is 85% of the matter in the universe made up of an unknown, invisible substance dubbed “dark matter”, we can’t even find all the small amount of normal matter that should be there.
This is known as the “missing baryons” problem. Baryons are particles that emit or absorb light, like protons, neutrons or electrons, which make up the matter we see around us. The baryons unaccounted for are thought to be hidden in filamentary structures permeating the entire universe, also known as “the cosmic web.”
But this structure is elusive and so far we have only seen glimpses of it. Now a new study, published in Science, offers a better view that will enable us to help map what it looks like.
The cosmic web provides the scaffolding of the large scale structure in the universe, predicted by the “standard cosmological model.” Cosmologists believe there is a dark cosmic web, made of dark matter, and a luminous cosmic web, made of mostly hydrogen gas. In fact, it is believed that 60% of the hydrogen created during the Big Bang resides in these filaments.
The web of gas filaments is also known as the “warm-hot intergalactic medium” (WHIM), because it is roughly as hot as the sun’s interior. Galaxies are likely to form at the intersection of two or more such filaments, where the matter is densest, with the filaments connecting all galaxy clusters in the universe.
So far, we haven’t been able to detect dark matter. This is because it does not emit or absorb light so it cannot be observed with usual telescopes. The cosmic web filaments are also very hard to find as they are very diffuse and they do not emit sufficient light to be detected.
Since the original prediction, there has been an intense search for the cosmic web, using a variety of methods.
One of these relies on bright objects that happen to lie in the background along the same line of sight as a gas filament. The hydrogen atoms in the filaments can absorb light at a specific wavelength in the ultraviolet. This can be detected as absorption lines in the light from the background object, when broken down into a spectrum by wavelength.
This method has been applied using quasars, which are very bright massive objects at large distances, and even with background galaxies.
Galaxies lighting up the web
The new study has managed to detect the gas in an entirely new way which allows two dimensional imaging of the cosmic web, rather than relying on the random location of a bright source behind the gas cloud used in absorption studies.
The object they studied, catchily named SSA22, is a proto-cluster, meaning it is a cluster of galaxies in its infancy. It is much farther away than previous measured bits of the cosmic web – its light travelled about 12 billion years to reach us. This means we are looking back in time to the early stages of the universe, allowing scientists to probe how the filaments first assembled.
Map showing the gas filaments (blue) running from the top to the bottom of the image. The white dots are very active star forming galaxies which are being fed by the filaments. Image iva Hideki Umehata.
A few years ago, a number of extremely bright, star-forming galaxies called “sub-millimeter galaxies” were detected near its center. This new study has found 16 such galaxies and eight powerful X-ray sources, a rare over-density of such objects at this early epoch. The objects provide copious amount of ionizing radiation to all of the hydrogen gas of the filaments, which makes it emit light that we can detect – a technique that holds much more promise than absorption.
Another mystery that this study helps to solve is the formation of sub-millimeter galaxies. The most widely agreed on explanation is that they form as a result of two normal galaxies merging, hence forming a massive galaxy with double the amount of light.
However, computer simulations show that these galaxies can grow from the cold gas pouring in from the neighboring cosmic web. This scenario is confirmed by this new study.
Detailed map
The new study paves the way for a more systematic, two-dimensional mapping of gas filaments that can tell us about their motions in space.
Future studies help further map the hidden cosmic web. In addition to looking at galaxy clusters full of bright objects, we can also trace the web’s emission in radio or X-ray wavelengths. However, the X-ray traces much hotter gas than the bulk of the WHIM. The proposed Athena X-ray observatory will provide a full picture of the hot filaments around the clusters of galaxies in the nearby universe.
Another proposed mission for beyond 2050 is to use the cosmic microwave background – the light left over from the Big Bang – as a “background light” and look for fine imprints left in it by the cosmic web.
All these tools will reveal the entire structure of the cosmic web and provide us with a definitive census of the matter in the universe.
What’s more, we know that baryons settle in the dark matter filaments of the universe to make their own filaments, like foam over an existing wave. This means that detailed maps of the gas filaments can help us trace the more hidden dark matter structure and, ultimately, help us understand its mysterious nature.
While a PhD student at Emory, Andrew Persichetti developed experiments based on a virtual town he created, called "Neuralville," above, and a simple video game. "One of my favorite things about being a scientist is getting to design experiments," he says.
Psychologists at Emory University have found that the human brain uses three distinct systems to perceive our environment — one for recognizing a place, another for navigating through that place and a third for navigating from one place to another.
For a new paper, they designed experiments involving a simulated town and functional magnetic resonance imaging (fMRI) to gain new insights into such systems. Their results, published by the Proceedings of the National Academy of Sciences (PNAS), have implications ranging from more precise guidance for surgeons who operate on the brain to better computer vision systems for self-driving cars.
“We’re mapping the functions of the brain’s cortex with respect to our ability to recognize and get around our world,” says Daniel Dilks, Emory associate professor of psychology and senior author of the study. “The PNAS paper provides the last big piece in the puzzle.”
The experiments showed that the brain’s parahippocampal place area is involved in recognizing a particular kind of place in the virtual town, while the brain’s retrosplenial complex is involved in mentally mapping the locations of particular places in the town.
While a PhD student at Emory, Andrew Persichetti developed experiments based on a virtual town he created, called "Neuralville," above, and a simple video game. "One of my favorite things about being a scientist is getting to design experiments," he says.
Psychologists at Emory University have found that the human brain uses three distinct systems to perceive our environment — one for recognizing a place, another for navigating through that place and a third for navigating from one place to another.
For a new paper, they designed experiments involving a simulated town and functional magnetic resonance imaging (fMRI) to gain new insights into such systems. Their results, published by the Proceedings of the National Academy of Sciences (PNAS), have implications ranging from more precise guidance for surgeons who operate on the brain to better computer vision systems for self-driving cars.
“We’re mapping the functions of the brain’s cortex with respect to our ability to recognize and get around our world,” says Daniel Dilks, Emory associate professor of psychology and senior author of the study. “The PNAS paper provides the last big piece in the puzzle.”
The experiments showed that the brain’s parahippocampal place area is involved in recognizing a particular kind of place in the virtual town, while the brain’s retrosplenial complex is involved in mentally mapping the locations of particular places in the town.
