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

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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 The Milky Way of 27,000 light years of us, this astronomical monster of 4 million masses solar cells have a diameter of its horizon that reaches 6 million kilometers, or about 15 times the distance between the Earth and the Moon.

Synchronized telescopes worldwide and 5 years of calculations!

Getting this picture was not easy! It all started with an observation campaign in April 2017 using very long baseline interferometry, 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 interferometer the size of the earth. By doing so will solution angle obtained 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. In fact, to achieve the dimension of the horizon, also called the shadow of the black hole, and brightness that surrounds it gives many clues to its properties: its size of course, its mass, but also and above all the dynamics of its accretion disk. This consists of fabric that the black hole attracts itself, heated to a very high temperature and which spins at gear relativists. 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 general theory of relativity established by Einstein 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 at the edge of a black hole, and investigate the basic physics of black holes and the very existence of black holes. 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 additional calculations!

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