A cool, sparkling ring has been detected around the gigantic black hole of our galaxy

Using the ALMA observatory, scientists have detected an undocumented cold gas band previously wrapped around the black hole at the heart of our galaxy.

The immediate area surrounding the supermassive black hole is quite intense. Called Sagittarius A *, this monster has a mass about 4 million times greater than that of our Sun. As befits a supermassive black hole of this size, it has succeeded, thanks to its intense gravitational influence, in collecting an assortment of cosmological marvels, including misplaced stars, interstellar dust piles, and various gases.

Much of the gas collected by Sagittarius A * runs around the black hole of an accretion disk. This donut-shaped ring extends from the horizon of the black hole events to a few tenths of a light-year. Astronomers had previously detected an extremely hot gas band in this accretion disk which, strangely, showed no sign of rotation around the black hole. A new research published today in Nature now describes a disk of cold interstellar gas, as well as traces of movement in the accretion disk.

"We were the first to image this elusive disc and study its rotation," said Elena Murchikova, lead author of the new article and astrophysicist at the Princeton Institute for Advanced Study, in a statement. National Observatory of Radioastronomy.

As noted, astronomers had already captured traces of the hot part of the ring gas. And by hot, we do not laugh. Its temperature is about 10 million degrees Celsius (18 million degrees Fahrenheit), which is two-thirds of the temperature found in the heart of the Sun. When the gas becomes very hot, it emits X-rays that can be detected from the Earth. Astronomers had also already detected colder gas near the black hole, but by far near the accretion disk.

To be clear, the "colder gas" is simply cold in comparison; it is still around 10,000 degrees Celsius or 18,000 degrees Fahrenheit. The relationship, if any, between this cold gas and the hot gas in the cloudy disk is not known.

But as the new study shows, there is also cooler gas near the supermassive black hole. Using the ALMA telescope in the Atacama Desert in Chile, astronomers have detected the weak millimeter wavelength signals from a ring of cold gas. These signals – the result of radiation on hydrogen atoms – traveled to Earth at a distance of 26,000 light-years, with little or no degradation along the way. The result is the very first image of the colder gas disk. Incredibly, it is located one hundredth of a light year from Sagittarius A * and has about 20,000 times the diameter of the black hole.

ALMA data also allowed Murchikova and his colleagues to track the location and movement of gas in the accretion disk. Due to the doppler radio effect, which produces offsets of blue (moving away from us) and red (pointing towards us), astronomers have been able to see that the gas was spinning slowly around the black hole . The amount of hydrogen in the cold area of ​​the disc was estimated to be about one tenth of the total mass of Jupiter.

Importantly, these observations provide new insights into how the supermassive black hole in the center of the Milky Way collects and devours surrounding matter. In the new study, the researchers estimate that Sagittarius A * engulfs a relatively small amount of matter, less than half a percent of the mass of the Moon per year.

These new observations are fascinating, but Murchikova said "we still do not understand the operation" of the accretion process at Sagittarius A *. A more in-depth exploration of new ALMA data, as well as observations from other observatories, should tell more about the monster parked in the heart of our galaxy.