Inside a pair of fused supermassive black holes, a new way to measure vacuum

Three years ago, the very first image of a black hole amazed the world. A black pit of nothing surrounded by a burning ring of light. This iconic image of the black hole in the center of the Messier 87 galaxy was brought into focus using the Event Horizon Telescope, a global network of radio-synchronized antennas that act as a giant telescope.

Now, two Columbia scientists have found a potentially simpler way to look into the abyss. Described in further studies in Physical examination letters and Physical examination D, their imaging technology could enable astronomers to study black holes smaller than the M87, a monster with a mass of 6.5 billion suns, housed in galaxies further away than the M87, which with 55 million sun light years is still relatively dense on our own. The Milky Way.

The technique has only two requirements. First, use a few fusing supermassive black holes. Second, look at the pair from an almost lateral angle. From this lateral perspective, when one black hole passes in front of another, you should be able to see a flash of light as the light ring from the farthest black hole is amplified by the black hole closest to you, a phenomenon known as gravitational lenses.

The lens effect is well known, but what the researchers discovered here was a hidden signal: a marked decrease in brightness corresponding to the “shadow” of the black hole behind. This subtle attenuation can last from a few hours to a few days, depending on the mass of the black holes and the proximity of their orbits. If you measure the duration of the trough, the researchers say, you can estimate the size and shape of the shadow cast by the event horizon of the black hole, the point without exit where nothing escapes, not even the light.

“It took years and significant effort from dozens of scientists to create this high-resolution image of the M87’s black holes,” said the study’s first author, Jordy Davelaar, a postdoctoral fellow at Columbia and the Center for Science. Computational Astrophysics from the Flatiron Institute. “This approach only works for the largest and closest black holes – the pair at the core of the M87 and potentially our own Milky Way.”

He added: “With our technique you measure the brightness of black holes over time, you do not have to solve all objects in space. It should be possible to find this signal in many galaxies.”

A black hole shadow is both its most mysterious and most 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 co-author Zoltan Haiman, a professor of physics at Columbia.

Black hole shadows can also hold the secret behind the true nature of gravity, one of the fundamental forces of our universe. Einstein’s theory of gravity, known as general theory of relativity, predicts the size of black holes. So physicists sought them out to test alternative theories of gravity in an attempt to reconcile two competing ideas about how nature works: Einstein’s general theory of relativity, which explains large-scale phenomena such as orbiting planets and the expanding universe, and quantum physics, which explains how tiny particles such as electrons and photons can occupy several states at once.

Scientists became interested in the proliferation of supermassive black holes after discovering a supposed pair of supermassive black holes in the center of a distant galaxy in the early universe. NASA’s planetary fighter Kepler Space Telescope scanned the small dives in brightness similar to a planet passing in front of its host star. Instead, Kepler ended up discovering flares of what Haiman and his colleagues claim to be a pair of fused black holes.

They called the distant galaxy “Spikey” for the peaks in brightness triggered by its supposed black holes that magnify each other with each full rotation via lens. To learn more about the eruption, Haiman built a model with his postdoc, Davelaar.

However, they were confused as their pair of simulated black holes produced an unexpected but periodic drop in brightness each time one rotated past the other. At first they thought it was a code error. But further verification made them trust the signal.

As they searched for a physical mechanism to explain it, they realized that at least in brightness corresponded closely to the time it took for the black hole closest to the viewer to pass in front of the shadow of the black hole on the back.

Researchers are now looking for more telescope data to try to confirm the drop they saw in the Kepler data, to confirm that Spikey is actually home to a few merged black holes. If all goes well, the technique can be applied to a handful of other putative pairs of fused supermassive black holes among the approximately 150 that have been discovered so far, awaiting confirmation.

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

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

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