Three years ago, the world saw the first ever image of a black hole. A black pit of nothingness is surrounded by a fiery ring of light. The image of the black hole at the center of the universe came into focus thanks to a global network of radio dishes acting as one giant telescope.
A pair of Columbia researchers have come up with an easier way to look into the depths. Astronomers could use their technique to study black holes smaller than M87, a monster with a mass of 6.5 billion suns, which is more distant than 55 million.
There are two requirements for the technique. You need a pair of black holes in the merging process. You have to be looking at the pair at a side-on angle. As one black hole passes in front of the other, you should be able to see a bright flash of light as the glowing ring of the black hole farther away is magnified by the black hole closest to you.
The lensing effect is well known, but what the researchers discovered here was a hidden signal: a dip in brightness corresponding to the shadow of the black hole in back. Depending on the size of the black holes and how close they are to each other, this subtle dimming can last from a few hours to a few days. If you measure how long the dip lasts, the researchers say, you can estimate the size and shape of the shadow cast by the black hole.
It took years and a massive effort by dozens of scientists to make that high-resolution image of the M87 black holes.
He said that with our technique, you don't need to resolve each object. It should be possible to find this signal in a lot of galaxies.
The shadow of a black hole is both informative and mysterious, as it 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.
One of the fundamental forces of our universe is gravity. Einstein's theory of gravity predicts the size of black holes. Physicists have sought them out to test alternative theories of gravity in an effort to reconcile Einstein's general relativity and quantum physics.
The researchers became interested in flaring supermassive black holes after spotting a suspected pair of supermassive black holes at the center of a far-off galaxy. The tiny dips in brightness corresponding to a planet passing in front of its host star were being scanned by the NASA space telescope. The flares of what Haiman and his colleagues claim are a pair of merging black holes were detected by the telescope.
The blur was named for the spikes in brightness triggered by the black holes magnifying each other on each full rotation via the lensing effect. Haiman and Davelaar built a model to learn more about the flare.
They were confused when their simulations produced a dip in brightness each time one of the black holes was in front of the other. They thought it was a coding mistake. Further checking made them trust the signal.
They realized that the time it took for the black hole closest to the viewer to pass in front of the shadow of the black hole in back was the same as the time it took for the brightness to go down.
The researchers are looking for other telescope data to confirm the dip they saw in the data to prove that Spikey is a pair of merging black holes. The technique could be applied to a few other suspected pairs of merging black holes that have been spotted so far and are awaiting confirmation.
Other opportunities may arise as more powerful telescopes come online. The Vera Rubin Observatory is set to open this year and is looking at more than 100 million black holes. When the LISA detector is launched into space, further black hole scouting will be possible.
Davelaar said that even if only a tiny fraction of the black hole binaries has the right conditions to measure the effect, they could find many of the black hole dips.
More information: Jordy Davelaar et al, Self-Lensing Flares from Black Hole Binaries: Observing Black Hole Shadows via Light Curve Tomography, Physical Review Letters (2022). DOI: 10.1103/PhysRevLett.128.191101Self-lensing flares from black hole binaries: general-relativistic ray tracing of black hole binaries, was written by Jordy Davelaar. There is a DOI titled "10/01/2019/physRevD.105.103010".
Journal information: Physical Review Letters , Physical Review D Citation: In a pair of merging supermassive black holes, a new method for measuring the void (2022, May 9) retrieved 9 May 2022 from https://phys.org/news/2022-05-pair-merging-supermassive-black-holes.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.
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