An international team of astronomers announced this Thursday that they managed to capture the image of the supermassive black hole located in the center of the Milky Way, three years after obtaining another similar one in the galaxy M87.
The collaboration, a project known as EHT (Event Horizon Telescope) presented, in several simultaneous press conferences, the “silhouette” of the black hole named Saggitarius A* on a luminous disk of matter.
Same principles of physics operate
This image is similar to that of the gigantic black hole in the distant galaxy M87, much larger than the Milky Way and that the EHT released in 2019.Scientists believe this proves that the same principles of physics operate at the heart of two systems of very different size.
Technically a black hole cannot be examined directly, since the object is so dense, and its gravitational pull so powerful, that even light cannot escape its force of attraction. But it is possible to detect the matter that circulates around it, before being engulfed.
Black holes are called stellar when they have a mass equivalent to three times that of the Sun, and they are classified as supermassive when their mass is equivalent to thousands, or even billions of Suns.
Sagittarius A* (Sgr A*) was named after being detected in the direction of the constellation Sagittarius. It has a mass of about four million suns and is about 27,000 light years from Earth.
Its existence had been suspected since 1974, when an unusual radio source was detected in the center of the galaxy.In the 1990s, several astrophysicists confirmed the presence of a supermassive compact object in that place, which earned them a Nobel Prize in Physics in 2020.The image that has been revealed this Thursday represents the first visual proof of that object.
Hours of observation, years of calculations
The EHT is an international network of eight radio astronomical observatories, including one located in Sierra Nevada (Spain) and another in the Atacama desert (Chile).
In 2019, the team achieved the historical image of the supermassive black hole of M87, equivalent to six billion solar masses and located 55 million light years away. The Sgr A+ therefore represents a “featherweight” in comparison.
“We have two completely different types of galaxies and two very different masses of black holes, but when you examine their edges, those holes look remarkably similar,” said Sera Markoff, co-chair of the EHT science council, in a statement accompanying the announcement.“That proves that the (Theory of) general relativity applies” in both cases, he added.
The image presented is the result of several hours of observation carried out essentially in 2017, and after five years of calculations and simulations carried out by more than 300 researchers from 80 institutes.
The image is much more difficult to obtain than that of M87* because the black hole at the center of the Milky Way is much smaller and because there are clouds of dust and gases that extend over thousands of light-years and obscure it.
The gas that surrounds it only needs twelve minutes to go around this galactic object, at almost the speed of light, while in the case of M87* it takes two weeks.That means the luminosity and configuration of the gas changed very rapidly during the observation.”It’s like you want to take a sharp picture of a dog that wants to catch its tail,” said Chi-Kwan Chan, a scientist at the EHT.
The two images that scientists now have, and their comparison, will allow the detailed study of the behavior of matter in extreme conditions, with plasma at “billions of degrees, powerful magnetic currents and matter that circulates at a speed close to light.” Professor HeinoFalcke, former head of the EHT scientific council that produced the image of M87*, explained.
Such harsh conditions will make it possible to explore phenomena such as the deformations of space-time near a supermassive object, predicted in the general theory of relativity that Albert Einstein formulated in 1915.
