Here is the first picture of the giant black hole in the middle of the Milky Way!

16.00 And here is a comparison of the two black holes from which we could get pictures, M87 * and Sagittarius A *! ” We have two completely different types of galaxies and two very different masses of black holes, but near the edge of these black holes they look surprisingly similar. Says Sera Markoff in communicated of the CNRS, Co-Chair of the Scientific Council of the EHT and Professor ofastrophysics theory at the University of Amsterdam, the Netherlands. ” This tells us that general theory of relativity controls these objects up close, and that any difference we see further away must be due to inequalities in the matter around the black holes. »

15.45. Many animations and information have been added. In particular, several images that explain how important the researchers’ work was: they had, on average, a gigantic amount of images. Now they intend to compare the two obtained images, which correspond to very different black holes: One weighs 4 million solar masses – Sagittarius A *, while the other represents 6.5 billion solar masses, M87 *! “We have pictures for two black holes – one at the big end and one at the small end of supermassive black holes inUniverse – we can therefore go much further in testing the behavior of gravity in these extreme environments than ever before. said Keiichi Asada, co-author of one of the six studies published in the journal. The Astrophysical Journal Lettersand researcher at the Department of Astronomy and Astrophysics in Taipei.

15:35. We suspected it, but scientists confirm it: the Sagittarius A * source is actually one black hole ! “We were surprised at how well the size of the ring matched the predictions of the general theory of relativityEinstein »said Geoffrey Bower, EHT Project Researcher, Department of Astronomy and Astrophysics, Academia Sinica, Taipei. that accretion disk orbits Sagittarius A * in minutes compared to several days or even weeks for M87 *, the researchers explain. It means that brightness changed rapidly during the observations made, and then complicated the calculations to get a picture.

The time is 15:07: this is a world first, the EHT researchers (Event Horizon Telescope) andESO (European South Observatory) has just unveiled the very first image of the black hole Sagittarius A *! “We’ve been so close many times before.” said in press conference ESO President Xavier Barcons. Located in the center of our Galaxy that The Milky Way of 27,000 light years from us, this astronomical monster of 4 million solar masses has a diameter of its horizon that reaches 6 million kilometers, or about 15 times the Earth-Moon distance.

Synchronized telescopes worldwide and 5 years of calculations!

Getting this picture was not easy! It all started with an observation campaign in April 2017 off interferometry very long base, also called VLBI. This observation technique consists of the simultaneous use of many radio telescopes in the world to create what is equivalent to a giant Earth-sized interferometer. By doing so will solution Angle size, which defines the smallest angle size that scientists are able to observe in detail, becomes so small that many normally invisible objects become visible. This is the case with M87 * and Sagittarius A *, two black holes whose apparent diameter is the same and which require a resolution that VLBI can reach. Take effect, M87 * is both much more massive and much further away than Sgr A * with its 6.5 billion solar masses and a distance of 50 million light-years, so its diameter visible from Earth corresponds to the diameter of Sgr A *.

The EHT collaboration makes it possible, thanks to this method, to achieve the largest angular resolution force in the world. Inside, during the observation in 2017, there were eight radio telescopes located across the globe: Mexico, Chile, Antarctica, USA, Spain. In each case the antenna radio is located at high altitude, to remove air pollution as much as possible. This process also requires a lot of preparation because the synchronization must be perfect. The only observation campaign by this method thus took place in 2017, more precisely from 4 to 14 April 2017. Then comes the data analysis! This phase is just as difficult as the first, and requires super computers, called correlators. In total, more than 350 people participated in this technological feat. Thus in 2019 very first picture of M87 * has been revealed, but not Sagittarius A *, as the scientific community had also expected.

Ultimately, the researchers will test general relativity

But what does this picture bring scientifically? Many things. First, getting the true look of a black hole makes it possible to compare it with models and simulations existing, to correct them. It therefore provides an opportunity to know more about black hole physics. Achieving the dimension of the horizon, also called the shadow of the black hole, and the brightness that surrounds it, actually gives many clues about its properties: its size of course, its mass, but also and above all the dynamics of its slice. of growth. This consists of the substance that the black hole attracts towards it, heated to very high temperatures and spins at relativistic speeds. In fact, it only takes 4 minutes and 30 seconds for the dust that makes up the disks to perform one orbit around the black hole, which, let us remember, has a horizon diameter of about 6 million kilometers!

It also allows astronomers to test the general relativity that Einstein established in 1916, in the strong field regime: when the particles become relativistic. They look at the curvature of light caused by gravitational effects, called ” gravitational lens ”: The black hole is so massive that the light does not follow a linear path when it passes near. This ability opens a new path to test general relativity in the strong field regime, study growth and flow processes on the edge of a black hole, and probe physical fundamental to black holes and the very existence of event horizons.

What to remember

  • In 2017, a major observation campaign was launched around the world to observe the two black holes M87 * and Sgr A *, which are 50 million light-years and 27,000 light-years away, respectively.
  • So, in 2019, on April 10, the first image of M87 * was revealed, but not the image of SgrA *, which still required many calculations.
  • This first picture finally came today, May 12, 2022, after three years of extra work! the reason for this “delay”: substance in the growth disk around the central black hole Sagittarius A * spins so fast that it completes a cycle in a few minutes. This makes the obtained images unstable, which requires much more computation time.

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