New! Measure black holes with light echoes

In this artist’s concept, a black hole’s intense gravity distorts the light coming from the Milky Way galaxy, located behind it. This phenomenon is called gravitational lensing. It can cause light from a single source to reach an observer several times, like echoes of light. And researchers said last week they’ve come up with a technique to detect the light echoes caused by gravitational lensing, from the vicinity around black holes. This technique could help them measure black holes. Image via ESA/Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org), N. Bartmann.

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New method for measuring black holes

If you were to watch a light flashing behind a black hole, a single flash might appear to you to repeat several times, like an echo. Why? Because massive objects like black holes warp the fabric of spacetime. That means light rays from a single source can take multiple different curved paths around black holes. And so some should take longer than others to reach our eyes. A team of astrophysicists reported this month (November 7, 2024) that it has devised a technique for detecting and measuring these light echoes from the warped space around black holes. They said their new technique could help pierce the mystery of black holes, whose gravity is so powerful that light passing too close is forever captured.

Black holes don’t emit light. So scientists are always looking for innovative ways to measure black holes, and thereby learn more about them. This team says its new technique could help measure the size and rotation of black holes. Scholars from the Institute for Advanced Study in Princeton, New Jersey, led this new research. The peer-reviewed Astrophysical Journal Letters published the new work on November 7, 2024.

Due to the immense gravity around a black hole, light rays get pulled around it via various curved routes. This diagram shows that, after a single flash of light near a black hole, some light rays travel straight to the observer. Others make one or more loops around the black hole first. The ones that travel a more looped path would look to us as if they were coming to us from a slightly different part of the sky. Image via George N. Wong et al.

Gravitational lensing around black holes

Since the first evidence for Einstein’s theory of general relativity in the year 1919, we’ve understood that massive objects do literally bend spacetime. We’ve known since then that when a light ray passes by an object with a huge gravitational pull, the path of the light will bend as it follows the curvature of space.

In more recent decades, astronomers have identified massive objects in space – including massive galaxies and giant black holes – that act as lenses. Such an object magnifies and distorts a light source located at a greater distance. Astronomers call the intervening objects gravitational lenses.

What’s new here is the method for detecting and measuring light that’s forced to travel multiple routes around an intervening black hole. George N. Wong is the study’s lead author. He said:

That light circles around black holes, causing echoes, has been theorized for years. But such echoes have not yet been measured. Our method offers a blueprint for making these measurements, which could potentially revolutionize our understanding of black hole physics.

How did they do it?

The scientists said they found a way to separate the faint light of individual echoes from the stronger light coming directly from matter circling the black hole. Their method relies on comparing the results of two very distant telescopes. It uses one on Earth and one in space, in a process called very long baseline interferometry. Very long baseline interferometry was the technique used to produce the first ever images of a black hole in 2019. That study used not just two, but multiple ground-based telescopes spread widely across Earth.

The team tested their technique by simulating tens of thousands of instances of light traveling around the supermassive black hole M87*. It’s located 55 million light-years away at the center of the galaxy M87.

And eureka! They found their method was able to measure how long the echoing photons were delayed before reaching an observer.

This image, which the European Southern Observatory released on March 27, 2024, shows the supermassive black hole at the center of the Milky Way in polarized light. A similar method could be used to detect light that echoes around black holes. Image via EHT Collaboration/ ESO.

Improving how we measure black holes

Importantly, the length of this echo delay is determined by both the mass and rotation of the black hole. And that’s why this research could be great news for astrophysicists. Lia Medeiros, one of the study’s authors, explained:

This method will not only be able to confirm when light orbiting a black hole has been measured, but will also provide a new tool for measuring the black hole’s fundamental properties.

We do have methods to calculate the spin and mass of black holes, but they’re not entirely reliable. The accretion disk – the bright, spinning ring of material around the black hole – can interfere with these measurements. Being able to verify these values via light echo delays would give scientists far greater confidence when measuring the fundamental properties of black holes.

The echo detection method has not yet been tried outside simulations. But, according to the researchers, putting the plan into practice is well within current scientific capabilities.

Bottom line: Astronomers say they’ve developed a new method to detect light that echoes around black holes. It could help them measure black holes’ size and rotation.

Source: Measuring Black Hole Light Echoes with Very Long Baseline Interferometry

Via Institute for Advanced Study

Read more: What is gravitational lensing?

Read more: Milky Way’s black hole in new image

The post New! Measure black holes with light echoes first appeared on EarthSky.

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In this artist’s concept, a black hole’s intense gravity distorts the light coming from the Milky Way galaxy, located behind it. This phenomenon is called gravitational lensing. It can cause light from a single source to reach an observer several times, like echoes of light. And researchers said last week they’ve come up with a technique to detect the light echoes caused by gravitational lensing, from the vicinity around black holes. This technique could help them measure black holes. Image via ESA/Hubble, Digitized Sky Survey, Nick Risinger (skysurvey.org), N. Bartmann.

The 2025 EarthSky Lunar Calendar is now available! Makes a great gift. Get yours today!

New method for measuring black holes

If you were to watch a light flashing behind a black hole, a single flash might appear to you to repeat several times, like an echo. Why? Because massive objects like black holes warp the fabric of spacetime. That means light rays from a single source can take multiple different curved paths around black holes. And so some should take longer than others to reach our eyes. A team of astrophysicists reported this month (November 7, 2024) that it has devised a technique for detecting and measuring these light echoes from the warped space around black holes. They said their new technique could help pierce the mystery of black holes, whose gravity is so powerful that light passing too close is forever captured.

Black holes don’t emit light. So scientists are always looking for innovative ways to measure black holes, and thereby learn more about them. This team says its new technique could help measure the size and rotation of black holes. Scholars from the Institute for Advanced Study in Princeton, New Jersey, led this new research. The peer-reviewed Astrophysical Journal Letters published the new work on November 7, 2024.

Due to the immense gravity around a black hole, light rays get pulled around it via various curved routes. This diagram shows that, after a single flash of light near a black hole, some light rays travel straight to the observer. Others make one or more loops around the black hole first. The ones that travel a more looped path would look to us as if they were coming to us from a slightly different part of the sky. Image via George N. Wong et al.

Gravitational lensing around black holes

Since the first evidence for Einstein’s theory of general relativity in the year 1919, we’ve understood that massive objects do literally bend spacetime. We’ve known since then that when a light ray passes by an object with a huge gravitational pull, the path of the light will bend as it follows the curvature of space.

In more recent decades, astronomers have identified massive objects in space – including massive galaxies and giant black holes – that act as lenses. Such an object magnifies and distorts a light source located at a greater distance. Astronomers call the intervening objects gravitational lenses.

What’s new here is the method for detecting and measuring light that’s forced to travel multiple routes around an intervening black hole. George N. Wong is the study’s lead author. He said:

That light circles around black holes, causing echoes, has been theorized for years. But such echoes have not yet been measured. Our method offers a blueprint for making these measurements, which could potentially revolutionize our understanding of black hole physics.

How did they do it?

The scientists said they found a way to separate the faint light of individual echoes from the stronger light coming directly from matter circling the black hole. Their method relies on comparing the results of two very distant telescopes. It uses one on Earth and one in space, in a process called very long baseline interferometry. Very long baseline interferometry was the technique used to produce the first ever images of a black hole in 2019. That study used not just two, but multiple ground-based telescopes spread widely across Earth.

The team tested their technique by simulating tens of thousands of instances of light traveling around the supermassive black hole M87*. It’s located 55 million light-years away at the center of the galaxy M87.

And eureka! They found their method was able to measure how long the echoing photons were delayed before reaching an observer.

This image, which the European Southern Observatory released on March 27, 2024, shows the supermassive black hole at the center of the Milky Way in polarized light. A similar method could be used to detect light that echoes around black holes. Image via EHT Collaboration/ ESO.

Improving how we measure black holes

Importantly, the length of this echo delay is determined by both the mass and rotation of the black hole. And that’s why this research could be great news for astrophysicists. Lia Medeiros, one of the study’s authors, explained:

This method will not only be able to confirm when light orbiting a black hole has been measured, but will also provide a new tool for measuring the black hole’s fundamental properties.

We do have methods to calculate the spin and mass of black holes, but they’re not entirely reliable. The accretion disk – the bright, spinning ring of material around the black hole – can interfere with these measurements. Being able to verify these values via light echo delays would give scientists far greater confidence when measuring the fundamental properties of black holes.

The echo detection method has not yet been tried outside simulations. But, according to the researchers, putting the plan into practice is well within current scientific capabilities.

Bottom line: Astronomers say they’ve developed a new method to detect light that echoes around black holes. It could help them measure black holes’ size and rotation.

Source: Measuring Black Hole Light Echoes with Very Long Baseline Interferometry

Via Institute for Advanced Study

Read more: What is gravitational lensing?

Read more: Milky Way’s black hole in new image

The post New! Measure black holes with light echoes first appeared on EarthSky.

from EarthSky https://ift.tt/tLv15R7