A team of researchers from Japan’s National Astronomical Observatory (NAOJ) is claiming that the groundbreaking image of the supermassive black hole at the center of our galaxy is not accurate.
The original image of Sagittarius A* was constructed from data taken by the Event Horizon Telescope Collaboration, which revealed the picture to the public in May 2022. It showed our galaxy’s central black hole as an ominous black cloud surrounded by a ring of light—the hole’s accretion disk. In its paper, the recent team suggests that the the object is more likely to have an elongated disk. The team published its proposed black hole structure in the Monthly Notices of the Royal Astronomical Society.
The 2022 image of the black hole depicts a four-million-solar-mass behemoth called Sagittarius A*. It is the first image of the object at our galaxy’s core and the Event Horizon Telescope (or EHT)’s second black hole image. The EHT’s first black hole image—the first-ever—depicted the black hole Messier 87 (M87), and published in 2019.
Black holes are regions of spacetime with gravitational fields so intense that not even light can escape them at a certain distance. That distance is the black hole’s event horizon. There is a field of glowing superheated matter around the event horizon: the accretion disk. The team’s recent paper focused on the accretion disk of Sagittarius A*, which they claim has a different shape than previously thought.
The EHT is a large radio observatory made up of a network of radio telescopes. EHT data reveal the black hole—an inherently invisible object, because light does not escape the event horizon—in its silhouette against a backdrop of its accretion disk.
“We hypothesise that the ring image resulted from errors during EHT’s imaging analysis and that part of it was an artefact, rather than the actual astronomical structure,” said Miyoshi Makoto, an astronomer at the NAOJ and co-author of the paper, in a Royal Astronomical Society release.
In its study, the team analyzed the same 2017 data on which the EHT Collaboration built its black hole image. But the team used a different method of analysis than the collaboration, indicating an elongated accretion disk compared to the doughnut structure seen in the 2022 image.
The recent team contends that the black hole’s accretion disk is elongated. In other words, it has a different structure than the ring-like disk imaged in 2022. The M87 black hole also appears to have a ring-like shape in the EHT image, which a later team developed into a polarized image of the object, complete with the structure of its magnetic fields.
In August, the EHT published a new method by which they improved the telescope’s resolution, hinting at sharper images of black holes in the near future. Should they follow through, future observations could clarify the actual structure of Sagittarius A*.
Even further down the road, a space-based mission to improve the sharpness of EHT images may launch. The mission concept describes a $300 million investigation of black holes’ photon rings—is called the Event Horizon Explorer.
Improving our understanding of the cosmos’ most extreme environments—the environments that foster black holes, neutron stars, and collisions of those two objects—will yield insights into the gravitational universe, as well as the core of our own galaxy.
