Did the Event Horizon Telescope film the supermassive black hole of the Milky Way Sgr A*?

We remember that on Wednesday April 10, 2019, at 3 p.m. in France,the international teamEvent Horizon Telescope (EHT) led by Shep Doeleman, researcher at the center ofastrophysics Harvard-Smithsonian, had made world headlines by publishing the historic image of the suspected supermassive black hole M87*. It is located in the center of the large elliptical galaxy M87 located approximately 53 millionlight years of the Milky Way.

We expected to see also the image of the supermassive black hole equally presumed at the heart of our Galaxy. With some masses respectively 4.3 million and 6 to 7 billion solar masses (M87*), the theory of general relativity predicted for these stars event horizon sizes of 25 million and 36 billion kilometers respectively. Taking into account the distances to the Earth, these compact objects have similar apparent diameters which are of the order of that of an apple or a golf ball observed from the Earth on the surface of the Moon.

Let us recall that the only thing that defines a black hole is the possibility of identifying the limits of a virtual closed surface surrounding a region of thespace-time which one cannot escape without being able to exceed the speed of light, which known physics prohibits. L’state of matter and spacetime below that surface inside a black hole is unknown and even if the theory of relativity alone implies the occurrence of a singularity at the core of the black hole where the curvature of space -time is infinite and the density of matter just as much (as demonstrated by the Nobel Prize in Physics Roger Penrose ), we do not know. In fact, the laws of quantum mechanics that Heisenberg and Schrödinger have revealed to us and which describe what is called the foam of space-timestrongly suggest that nothing like this probably happens.

Finally, it may well be that the objects we take for black holes are in fact stars almost as compact, thus behaving in many respects like black holes from an astrophysical point of view, but without event horizon real, so not black holes as Hawking himself had envisioned. It could be superstring ballsof gravestars and even of wormholes !

Unfortunately, this Wednesday, April 10, 2019, no image of the supermassive black hole of the Milky Way associated with the famous source radio Sagittarius A* (Sgr A* for short), had not been shown because the data collected by the international network of radio telescopes making it possible to obtain a virtual instrument almost the size of the Earth to achieve the power of resolution necessary for the observations had proved to be more difficult to deal with than expected. The researchers of the EHT collaboration, however, continued to both take new data and improve their processing.

Needless to say therefore that for more than a week the tension has been rising following an announcement which promises us news concerning Sgr A*.

It was a joint press release from European Southern Observatory (ESO) and theEvent Horizon Telescope (EHT) explaining that on May 12, 2022, thanks to the global village and the WWWthere will be an online conference on this subject that can be followed live from 3:00 p.m. in France.

As a prelude to this conference and to try to imagine its content, let’s recall what Shep Doeleman explained to AFP in 2019 “For years I told people we were going to get a picture of a black hole and they told me they would believe me when they saw it. The scientific community expressed a degree of skepticism, which is normal. When you finally get the proof, when you achieve such a breakthrough, you really feel the satisfaction of having given birth to a new field of research.he continues. We are now in the era of high precision images of black holes. We can make space-time maps for the first time”. Better, according toastrophysicistalready at that time, his colleagues were working to produce a video from the mountains of recorded data. “By the end of the next decade, we will be making high-quality, real-time movies of black holes that will reveal not only their appearance but also their behavior on the cosmic stage”assured Shep Doeleman.

He also explained that it is precisely because of the very dynamic and turbulent accretion of matter on the central black hole of the Milky Way that we had not yet had an image of Sgr A*. But this also means very precisely that one should obtain images showing a clear evolution over time. “It takes about a month for matter to circulate around M87*. But for Sagittarius A*, it only takes half an hour. In one night of observation, Sgr A* can change in front of us”, he added, also explaining that: “It is possible that we will make a fairly raw first film. Ideally, more than telescopeson Earth or in orbit earthly, to increase the resolution. But we will refine this over time. It may be like the first films of the cinema”.

Finally, remember that it is the French astrophysicist and cosmologist Jean Pierre Luminetas he explained several times and with many details on the versions french and English of blog that Futura made available to him, which was the first in the late 1970s to calculate on computer the visual appearance of a black hole surrounded by an accretion disk. With his colleague Jean-Alain Marck, he then carried out simulations showing the appearance of such an object from several angles and we can therefore think that we will be able to make comparisons between M87* and Sgr A* which should not be presented under the same orientation eyes of the noosphere.

The members of the EHT collaboration could therefore surprise us tomorrow with breathtaking images of Sgr A*. We can also reasonably expect new constraints on new physics which could replace the theory of relativity ofEinstein and of course also on the existence or not of an event horizon.

Einstein’s theory of general relativity is indeed not the only possible one compatible with the theory of Relativity and based on the possibility of space-time curvature. From equations different being reduced to those of Einstein in certain situations just as it was the case for the equations of Newton which are borderline cases of those of Einstein are indeed considered and studied for more than 50 years like the famous tensor-scalar theories.

Invalidating Einstein’s theory in favor of these variants could give us keys to solving the enigmas related to the black matter and thedark energy. Conversely, supermassive black holes are thought to possess an outer space-time geometry that is that of a rotating Kerr black hole. This involves movements very precise for the matter and trajectories which are just as precise for the light rays which are produced by the heated matter of an accretion disk around certain black holes.

If the agreement is good enough between the predictions of Einstein’s theory for a Kerr black hole and the new observations made by the members of the EHT collaboration, then it could lead to the refutation of exotic and rather unbelievable alternatives to the black hole theory.

One can get an idea of ​​how the observations of Sgr A* can lead to explorations of alternative theories to that of Einstein and to the solutions of their equations describing alternatives to those of Einstein’s general relativity by consulting the video below which already spoke of these tests carried out with the EHT, but for M87*.

To refresh your memory about the EHT’s global network of radio telescopes and what it can observe for the so-called shadow (shadow, in English) of a black hole, you can watch the video below.