Observing the collision of two black holes has provided astronomers with a new tool for measuring black holes in distant galaxies.

How did researchers observe the collision of these two black holes?

IN Columbia University scientists have devised a potentially simpler way to study black holes. Outlined in additional studies in Physical examination letters and Physical examination D, their imaging technique could allow astronomers to study black holes smaller than M87 – which have a mass of 6.5 billion suns – sheltered in galaxies farther from M87; 55 million light-years away, it’s still relatively close to the Milky Way.

Their technique has only two requirements. First, a pair of supermassive black holes is needed in the merging headache. Second, the two black holes that collide should be viewed at an almost lateral angle. From this point of view, when one black hole passes in front of another, a bright flash must appear, as the luminous ring of the black hole increases farther from the nearest black hole to the observer, a phenomenon known as gravitational lenses.

What is the effect of lenses?

The effect of the lens is well known, but researchers have found a hidden signal: a distinctive decrease in brightness, corresponding to the “shadow” of the black hole in the back. This fine eclipse can last from several hours to several days; it depends on the size of the black holes and how closely their orbits are intertwined.

“If you measure how long the decline lasts, you can estimate the size and shape of the shadow cast from the event horizon of the black hole, the dead end point where nothing comes out, not even the light,” the researchers explained.

“It took years and a lot of effort by dozens of scientists to make this high-resolution image of M87 black holes,” said Jordi Davelaar, the study’s first author, a postdoc in Colombia and the Flatiron Institute’s Center for Computational Astrophysics. “This approach only works for the biggest and closest black holes – the pair at the heart of the M87 and potentially our own Milky Way.

“With our technique you measure the brightness of black holes over time; you do not need to resolve each object spatially. It should be possible to find this signal in many galaxies. “

What does the shadow reveal?

The shadow of a black hole is considered the most mysterious and informative feature. “This dark spot tells us about the size of the black hole, the shape of space-time around it, and how matter falls into the black hole near its horizon,” said Zoltan Hyman, co-author of the study and professor of physics in Colombia.

In addition, the shadows of black holes can also hide the secret of the true nature of gravity, one of the main forces of our universe. Einstein’s theory of gravity, known as the general theory of relativity, predicts the size of black holes. Therefore, physicists have sought them out to test alternative theories of gravity to reconcile two competing ideas about how nature works: Einstein’s general theory of relativity – which explains large-scale phenomena such as orbital planets and the expanding universe – and quantum physics. , which describes how small particles such as electrons and photons can occupy multiple states at once.

What was found when observing a suspected pair of supermassive black holes?

After noticing a putative pair of supermassive black holes, researchers are interested in the eruption of supermassive black holes at the center of a distant galaxy in the early universe. NASA’s Kepler Space Telescope, which chases the planets, scans for small drops in brightness corresponding to a planet passing in front of the host star. Instead, Kepler discovered the eruptions of what Hyman and his colleagues thought were a pair of merging black holes.

The distant galaxy was named “Spikey” because of the brightness spikes caused by what scientists suspected to be black holes that magnified each other with each full rotation through the lens effect. To learn more about this eruption, Hyman built a model with his postdoctoral fellow, Davelaar.

However, the researchers were confused when their simulated pair of black holes caused an unexpected but periodic drop in brightness each time it orbited another. At first they thought it was a coding error; however, further investigations led them to trust the signal.

As they searched for a physical mechanism to explain it, they realized that any drop in brightness coincided with the time it took for the black hole closest to the viewer to pass in front of the shadow of the black hole behind.

How will this decline be explained?

Scientists are currently looking for additional telescopic data to confirm the decline they observed in Kepler’s data to confirm that Spike is hiding a pair of merging black holes. If successful, the technique could be applied to a handful of other alleged pairs of merging supermassive black holes among the 150 observed so far awaiting confirmation.

As more powerful telescopes appear online in the coming years, other possibilities may arise. The Vera Rubin Observatory, due to open this year, has views of more than 100 million supermassive black holes. Further exploration of black holes will be possible when NASA’s gravitational wave detector, LISA, is launched into space in 2030.

“Even if only a small fraction of these binary black holes have the right conditions to measure the effect we are proposing, we could find many of these black hole declines,” Davelaar concluded.

Scientific advancements made by observing two black holes colliding

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