Scientists say there's something wrong with the famous black hole image: ScienceAlert

Remember that stunning “first image” of the black hole Sagittarius A* (Sgr A) at the heart of the Milky Way? Well, that may not be entirely accurate, according to researchers at the National Astronomical Observatory of Japan (NAOJ).

Instead, the accretion disk around Sagittarius A* may be more elongated, rather than the circular shape we first saw in 2022.

Scientists at NAOJ applied different analysis methods to Sgr A* data first captured by the Event Horizon Telescope (EHT) team. The EHT data came from a network of eight ground-based radio telescopes. The original analysis showed a bright toroidal structure surrounding a dark central region.

The reanalysis that results in a different shape indicates something about the movements and distribution of matter in the disk.

In fairness to both groups, analyzing radio interferometry data is very complex. According to NAOJ astronomer Miyoshi Mikato, the rounded appearance may be due to the way the image was created.

“We assume that the annular image resulted from errors during the EHT's imaging analysis and that this part of it was an artifact, not the actual astronomical structure,” Miyoshi suggested.

Explaining the appearance of a black hole

So, what does Archer A* look like in the NAOJ reanalysis?

“Our image is slightly stretched in the east-west direction, and the eastern half is brighter than the western half,” Miyoshi said.

“We think this appearance means that the accretion disk surrounding the black hole is rotating at about 60 percent of the speed of light.”

The accretion disk is filled with super-hot material, “circling the drain” as it were, flowing into the 4 million solar-mass black hole. As it rotates through the accretion disk, friction and the action of magnetic fields heat the material. This causes it to glow, mostly in X-rays and visible light, as well as emitting radio emissions.

Various factors also affect the shape of the accretion disk, including the rotation of the black hole itself. In addition, the rate of accretion (i.e. how much matter falls into the disk), as well as the angular momentum of the matter, all affect the shape.

The black hole's gravitational force also distorts our view of the accretion disk. This type of “mirror fun” distortion makes it very difficult to photograph. As it turns out, either view of the disk's actual shape — the original circular view of the EHT or the elongated view of the NAOJ — can be accurate.

So why the different views on black holes?

How did the teams arrive at two slightly different views of Sagittarius A* using the same data?

“No telescope can capture an astronomical image perfectly,” Miyoshi noted. For EHT observations, it turns out that interferometric data from widely associated telescopes can contain gaps. While analyzing data, scientists have to use special techniques to build a complete picture. This is what the EHT team did, resulting in the “rounded black hole” image.

Miyoshi's team published a paper describing their findings. In it, they suggest that the toroidal structure in the 2022 EHT image is an artifact caused by the bumpy point spread function (PSF) of the EHT data.

The PSF describes how an imaging system interacts with a point source in the area it is looking at. It helps give a measure of how much blur is caused by imperfections in the optics (or in this case, gaps in the interferometric data). In other words, he had problems “filling in” the gaps.

The NAOJ team reanalyzed the data and used a different mapping method to fill in data gaps. This resulted in an elongated shape for the accretion disk Sgr A*.

Half of the disc is brighter and they suggest that this is due to Doppler enhancement as the disc rotates rapidly. They suggest that the newly analyzed data and extended image show part of the disk that lies a few Schwarzschild radii away from the black hole, rotating very rapidly, and can be seen from an angle of 40°-45°.

What's next?

This reanalysis should help contribute to a better understanding of the actual shape of the accretion disk Sgr A*. The EHT study of Sagittarius A* that led to the 2022 release of the image was the first detailed attempt to map the region surrounding the black hole.

the The EHT Consortium is working on improvements To produce better and more detailed interferometric images of this and other black holes. Ultimately, this should lead to more accurate views.

Follow-up studies should help fill in any gaps in accretion disk observations. In addition, detailed studies of the nearby environment surrounding the black hole should give more clues about the black hole hiding inside the disk.

This article was originally published by The universe today. Read the original article.