The supermassive black hole in the center of our galaxy was finally photographed

The international collaboration between the astronomers EHT and the European Southern Observatory (ESO) on Thursday proved in the picture the existence of Sagittarius A *, a supermassive black hole in the heart of our Milky Way. And this, three years after the first image of a black hole, located in a distant galaxy.

“I can present you with the picture of black hole Sgr A * at the heart of the galaxy, “EHT project manager Huib Jan Van Langevelde announced in applause at a news conference in Garching, Germany.

It was a strange ballet of stars in the center of the Milky Way, which at first made it possible to understand that there was probably a black hole there: Andrea Ghez and Reinhard Genzel received Nobel Prize in Physics in 2020 for their “discovery of a supermassive compact object at the center of our galaxy”.

The team had even managed to determine its exact mass. But thanks to the observations revealed today, its size could be assessed. Two essential parameters to prove its existence with certainty.

Sagittarius A *, which owes its name to its detection in the direction of the constellation Sagittarius, has a mass of about four million suns and is 27,000 light-years from Earth. Its existence has been assumed since 1974, with the detection of an unusual radio source at the center of the galaxy.

The drug swallowed

Technically, one cannot see a black hole because the object is so dense and its gravity so powerful that not even light can escape from it. But we can observe the material circulating around it before it is swallowed: its silhouette stands out on this luminous disc.

“We have direct evidence that this object is a black hole,” explained Sara Issaoun, of the Harvard Center for Astrophysics, describing “the gas cloud. [autour du trou noir] which emits radio waves and which we have observed ”.

“The object is surrounded by a surface called the event horizon,” explains astrophysicist Roland Walter, of the Observatory at the University of Geneva, a specialist in black holes. At the microphone on the Forum, he explains that the shadow in the middle is “the signature of the presence of the black hole”. It was harder to grasp because it is “much smaller, less luminous and there is a lot of material between it and us,” he notes.

Telescopes need to observe it much longer to get something useful: “By recording this data and correlating it, we can reconstruct this image”.

Second historical picture

The technique used for this image is millimetric radio interferometry. EHT, an international network of eight radio astronomical observatories, in 2019 brought the historic image of M87 *, a supermassive black hole of six billion solar masses in its galaxy, Messier 87, located 55 million years ago. -light.

>> Read: Mankind sees a black hole for the first time in history

Now equipped with eleven observatories, EHT has portrayed Sgr A * with its four million solar masses … a featherweight in the bestiary of supermassive black holes.

Scientists see this as proof that the same mechanisms of physics are at the heart of two systems of very different sizes: “Black holes are absolutely fascinating objects. They are predicted by Einstein’s general theory of relativity, but modern physics is heavily dependent on quantum mechanics. two are not compatible and do not predict the same thing about what happens on the surface of a black hole, “notes Roland Walter.

“And the black hole is the place in the universe where we manage to put these two theories together” and maybe even find a theory that unites them! This is not the case at the moment: “It’s a place where you can really do basic physics”, the astrophysicist rejoices.

>> A short film explaining how EHT works (in English, with French subtitles):

Stéphanie Jaquet and the agencies

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