New Debate: Can a Black Hole’s Photon Ring Be Detectable?
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If real, thin ring of light will probe gravity around black hole in a new way
The first image of a black hole may be hiding a treasure, but physicists disagree on whether it will ever be found.
A team of scientists say they have detected a photon ring, a thin halo of light around a supermassive black hole in the galaxy M87. If real, the photon ring would provide a new probe into the intense gravity of a black hole. But other scientists dispute this claim. Despite several headlines suggesting that a photon ring has been detected, many physicists are still not convinced. Announced in 2019 by scientists at the Event Horizon Telescope, or EHT, the first image of a black hole shows donut-shaped light from hot matter circling the shadow. of a black hole (SN: 4/10/19). But according to Einstein’s general theory of relativity, a thinner hoop should be superimposed on this thick donut. This ring is created by photons, or particles of light, orbiting the black hole, suspended by the bomber’s gravity before escaping and heading towards Earth.
Thanks to this rotation, the photons will provide “gravitational traces”, revealing more clearly, said astrophysicist Avery Broderick of the University of Waterloo and the Perimeter Institute for Theoretical Physics in Canada. properties of black holes. He and his colleagues, a small group of scientists from the EHT collaboration, used a new method to unravel that fingerprint, they reported Aug. 10 Journal of Astrophysics.
Creating images with the EHT is more than just a point-and-shoot (SN: 4/10/19). The researchers gathered data from a group of EHT observatories scattered around the world, using different computational techniques to reconstruct a picture. Broderick and his colleagues created a new image of the black hole assuming it has both diffuse emission and a thin ring. For three out of four observation days, the data matched the images with the added thin rings better than those without the rings. But this method has been strongly criticized. Physicist Sam Gralla of the University of Arizona in Tucson said: “The claim of photon ring detection is nonsense.
One major point of contention: the photon ring is brighter than expected, emitting about 60% of the light in the image. According to the forecast, it will be like 20%. “It’s a huge red flag,” said physicist Alex Lupsasca of Vanderbilt University in Nashville. More light is expected to come from the black hole’s main glowing donut than from the thin ring of photons.
According to Broderick and his colleagues, this unexpected brightness occurs because some of the light from the main luminous region is bundled into the photon ring. Thus, the apparent brightness of the ring depends not only on the light emitted by the ring. The same effect appeared when testing the method on simulated data, the researchers noted.
But this hodgepodge of what appears to be a photon ring with other lights isn’t very compelling evidence, critics say. “If you’re going to claim to have seen a ring of photons, I think you have to do a better job,” says Dan Malone, an astrophysicist at the University of Arizona. new paper.
The new results only suggest that the thin ring added fits the data better, not whether its shape is related to the photon ring. Are you looking at the , or are you simply looking at unrelated structures in the image?
But Broderick argues that the features of the ring—the fact that its size and position are predictable and consistent from day to day—support Photon’s interpretation of the ring. Meanwhile, in a similar independent analysis, Gralla of the University of Arizona and physicist Will Lockhart found no evidence of a photon ring, report a paper submitted to arXiv.org on August 22. Their analysis partly differed from Broderick et al.’s because they limited the brightness of the photon ring.
To provide compelling evidence for a photon ring, some scientists have proposed expanding the EHT observatory to include a cosmic telescope (SN: 3/18/20). The farther the telescopes are in the network, the more detail they may be able to see. This may include photon rings.
“With the detection of the photon ring, it would be the best thing in physics this year, if not years.”
A.E. Broderick et al. The photon ring in M87*. Astrophysical Journal. Vol. 935, August 10, 2022, p. 61. doi: 10.3847/1538-4357/ac7c1d.
W. Lockhart and S.E. Gralla. How narrow is the M87* ring? II. A new geometric model. arXiv:2208.09989. Submitted August 22, 2022.