In a pair of merging supermassive black holes found a new method to measure emptiness

(ORDO NEWS) — Three years ago, the first ever image of a black hole stunned the world. A black pit of nothingness surrounded by a fiery ring of light.

This iconic image of the black hole at the center of the Messier 87 galaxy comes from the Event Horizon Telescope, a global network of synchronized radio dishes that act as one giant telescope.

Now, a pair of researchers at Columbia University have come up with a potentially easier way to peer into the abyss.

Described in additional research in Physical Review Letters and Physical Review D, their imaging technique could allow astronomers to study black holes smaller than M87, a 6.5 billion sun-mass monster located 55 million light-years from our Milky Way.

The method has only two requirements. First, we need a pair of supermassive black holes that are in the process of merging. Secondly, you need to look at the couple almost at a side angle.

From this lateral vantage point, as one black hole passes in front of another, you should see a bright flash of light as the far black hole’s luminous ring is magnified by the black hole closest to you, a phenomenon known as gravitational lensing.

The lensing effect is well known, but the researchers found a hidden signal: a distinct dip in brightness corresponding to the black hole’s “shadow” from behind. This subtle decrease in brightness can last from hours to days, depending on how massive the black holes are and how closely intertwined their orbits are.

By measuring how long the blackout lasts, the researchers say, one can estimate the size and shape of the shadow cast by a black hole’s event horizon – a point from which there is no way out, from which nothing escapes, not even light.

“It took years and the enormous effort of dozens of scientists to image M87’s black holes at high resolution,” said Jordi Davelaar, PhD, PhD, from Columbia University and the Flatiron Institute’s Center for Computational Astrophysics.

“This approach only works for the largest and closest black holes – the pair at the center of M87 and possibly our own Milky Way.”

He added: “In our method, you measure the brightness of black holes over time, you don’t have to compute each object spatially. This signal must be found in many galaxies.”

The shadow of a black hole is both its most mysterious and informative feature. “This 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 near its horizon,” said study co-author Zoltan Hyman, professor of physics at Columbia University.

The shadows of black holes may also hold the secret of the true nature of gravity, one of the fundamental forces of our universe. Einstein’s theory of gravity, known as general relativity, predicts the size of black holes.

So physicists are looking for them to test alternative theories of gravity, trying to reconcile two competing ideas about how nature works: Einstein’s general theory of relativity, which explains such large-scale phenomena as rotating planets and an expanding universe, and quantum physics, which explains how tiny particles , such as electrons and photons, can simultaneously be in several states.

Researchers became interested in flaring supermassive black holes after spotting a putative pair of supermassive black holes at the center of a distant galaxy in the early universe.

NASA’s planet-finding Kepler Space Telescope scanned tiny dips in brightness corresponding to a planet passing in front of its host star. Instead, Kepler detected flashes of what Hyman and his colleagues claim is a pair of merging black holes.

They named the distant galaxy “Spikes” for the bursts of brightness caused by its supposed black holes magnifying each other with each complete rotation due to a lensing effect. To learn more about the outbreak, Hyman built a model with his co-author Davelaar.

However, they were puzzled when a pair of black holes they modeled produced an unexpected but periodic dip in brightness each time one orbited in front of the other. At first they thought it was a coding error. But further testing led them to believe the signal.

Looking for a physical mechanism to explain it, they realized that each dip in brightness corresponds exactly to the time it takes for the black hole closest to the viewer to pass in front of the shadow of the black hole behind.

The researchers are now looking for data from other telescopes to try to confirm the dip they saw in the Kepler data and to confirm that Spike is indeed the home of a pair of merging black holes.

If all is confirmed, then this method could be applied to several other putative pairs of merging supermassive black holes out of the 150 or so that have been seen so far and await confirmation.

With the advent of more powerful telescopes in the coming years, other possibilities may emerge. The Vera Rubin Observatory, due to open this year, targets more than 100 million supermassive black holes. Further exploration of black holes will become possible when NASA’s LISA gravitational wave detector is launched into space in 2030.

“Even if only a tiny fraction of these black hole binaries have the right conditions to measure our proposed effect, we should be able to find many such black hole dips,” Davelaar said.


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