Astronomers find an Einsteinian hack to image black holes

The study of black holes has advanced enormously in recent years. In 2015, the first gravitational waves were observed by scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO). This finding confirmed what Einstein predicted a century earlier with general relativity and offered new insight into the merging of black holes. In 2019, scientists with the Event Horizon Telescope (EHT) Collaboration shared the first image of a supermassive black hole (SMBH), located at the center of the M87 galaxy.

Earlier this month, the EHT announced that they had also captured the first image of Sagittarius A*, the black hole at the center of the Milky Way. And just in time for Black Hole Week (May 2 to May 6), a pair of Columbia University researchers announced a new and potentially easier way to study black holes. In particular, their method could enable the study of black holes smaller than M87* in galaxies further away than the M87 galaxy.

This new imaging method was developed by Zoltán Haiman (professor of astronomy at Columbia University) and Jordy Davelaar, theoretical astrophysicist at Columbia’s Flatiron Institute in New York, and member of the EHT collaboration. Their method was outlined in complementary studies recently published in Physical Assessment Letters and Physical assessment D† As they point out in these articles, their technique combines two techniques: interferometry and gravitational lensing.

The first technique involves using multiple instruments to capture light from distant sources and then combining it to create a composite image. This technique allowed the EHT collaboration to capture images of the bright rings around M87* and Sagittarius A* (among other objects). In the latter case, the gravity of a massive object (such as a black hole or galaxy) is used to amplify and amplify the light from a more distant object.

As Haiman and Davelaar explain, when astronomers view a binary black hole system from the side as one passes in front of the other, astronomers will use the gravitational pull of the nearest black holes to magnify the bright disk of the more distant black holes. However, these observations will also reveal another interesting feature. If two black holes pass in front of each other, Haiman and Davelaar said, there will be a noticeable dip in brightness that matches the “shadow” of the more distant black hole.

Depending on how massive the black holes are and how closely their orbits are intertwined, these dips can last from a few hours to several days. The length of the dip can also be used to estimate the size and shape of the shadow cast by the black holes event horizon, the point at which nothing (not even light) can escape its gravitational pull. As Davelaar explained in a recent issue of Columbia News:

“It took years and a massive effort by dozens of scientists to create that high-resolution image of the M87 black holes. That approach only works for the largest and closest black holes — the pair at the heart of M87 and possibly our own Milky Way. [W]With our technique you measure the brightness of the black holes in time, you do not have to solve every object spatially. This signal should be able to be found in many galaxies.”

Gravity lenses use the gravity of a large object to bend, brighten, and distort the light of other objects behind it. Credit: NASA/ESA/L. Calcada

As Haiman added, the shadow of a black hole is its most mysterious and informative feature. “That dark spot tells us about the size of the black hole, the shape of the space-time around it, and how matter falls into the black hole on the horizon,” he said. Haiman and Davelaar became interested in this phenomenon after Haiman and a team of colleagues discovered a suspected pair of supermassive black holes (“Spikey”) in 2020 at the center of a galaxy that existed during the early Universe.

The discovery came when the team was examining data from the Kepler Space Telescope to monitor distant stars for small brightness drops, which is used to confirm the presence of transiting exoplanets. Instead, the Kepler data showed evidence that the flare-up effect was caused by a pair of transiting black holes visible from the side. Its nickname was due to the spikes in brightness caused by the suspected lensing effect of the black holes as they passed in front of each other.

To learn more about the torch, Haiman enlisted the help of his postdoc (Davelaar) to construct a model for this torch effect. While the model confirmed the spikes, it also revealed a periodic dip in brightness that they couldn’t explain. After ruling out the possibility that this was due to errors in the model, they determined that the signal was real and looked for a physical mechanism that could explain it. Eventually, they realized that each dip closely matched the time it took the black holes to make transits relative to the observer.

The detection of this shadow could have huge implications for both astrophysicists and quantum physicists. Astrophysicists have searched for these shadows as part of an ongoing effort to test general relativity under the most extreme conditions and environments. These tests could lead to a new understanding of how gravity and quantum forces interact, allowing physicists to finally solve for how the four fundamental forces of nature work together: electromagnetic, weak nuclear forces, strong nuclear forces and gravity.

For decades, scientists have understood how three of the forces that govern all matter-energy interactions work. While general relativity describes how gravity (the weakest of the four forces) works on its own, all attempts to find a way to explain this in quantum terms have failed. As a result, a theory of “quantum gravity” or Theory of Everything (ToE) has eluded even the greatest scientific minds. This includes Einstein and Stephen Hawking, who have devoted most of their scientific careers to finding one.

Meanwhile, Haiman and Davelaar are currently looking for other telescope data around the Kepler. to confirm observations and verify that “Spikey” really does harbor a pair of merging black holes. If and when their technique is confirmed, it will likely be applied to the approximately 150 pairs of merging SMBHs that have been observed but are still awaiting confirmation. In the coming years, next-generation telescopes will come online, providing more opportunities to test this technique.

Examples include the Vera C. Rubin Observatory, a massive telescope in Chile set to open later this year. Once operational, Rubin will conduct the 10-year Legacy Survey of Space and Time (LSST), observing more than 100 million SMBHs. By 2030, NASA’s Laser Interferometry Space Antenna, a space-based gravitational wave detector, will also come online, providing even more opportunities to study merging black holes. With so many candidates available for study, scientists don’t have to wait too long for a breakthrough.

“Even if only a small fraction of these black hole binary stars have the right conditions to measure our proposed effect, we could find many of these black hole dips,” Davelaar said.

Read further: Columbia News

This article was originally published on Universe today by means of Matt Williams† Read the original article here.

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