A first image of the black hole at the center of the Milky Way is revealed

The first image of the black hole at the center of our galaxy, the Milky Way, was revealed on Thursday by an international team of researchers. The technical capabilities are fully in line with astrophysicists’ predictions, astounding the scientific community.

The black hole sits at the center of Sagittarius A*, a radio frequency flare 27,000 light-years from Earth. Our galaxy orbits this object, which has so far defied the most powerful telescopes due to its low luminosity.

The Event Horizon Telescope (EHT), a network now made up of 11 radio telescopes spread across the Earth, has managed to pierce this fuzzy halo to discover a shadowed disc: the black hole’s “shadow”. . This silhouette is defined by the glowing cloud of gas spinning around the supermassive object from which nothing can escape.

“Wow! », Started with emotions Sara Issaoun, a member of the EHT team, spoke at the press conference organized by the European Southern Observatory in Munich. “For decades we have known that there is a compact object there, four million times more massive than ours Sun,” she said. Today we have direct evidence that this object is a black hole.”

Sagittarius A* is 1,600 times less massive than the black hole at the center of the galaxy Messier 87, whose image, also captured by the EHT, made headlines in 2019. At the time, it was the first image of a black hole that had never been obtained.

The discovery announced on Thursday is proving to be a much more difficult proposition on a technical level.

By comparison, if Sagittarius A* were the size of a donut, Messier 87* would be the size of a soccer stadium. Also, the black hole’s glowing ring at the center of our galaxy is moving rapidly, unlike that of its distant big brother. Years of analysis were therefore necessary to arrive at the results presented on Thursday, which are based on observations from 2017.

Despite the size differences between the two “photographed” black holes, their silhouettes are very similar. “This similarity shows us a key aspect of black holes: Regardless of their size or their environment, when you get to the boundary of a black hole, gravity takes over,” Frau explained.me Issaoun, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics.

Julie Hlavacek-Larrondo, a black hole specialist at the University of Montreal, called Thursday’s results a “huge success.” She attended the digital press conference from a meeting at the Center for Research in Astrophysics of Quebec. “We listened to the presentation together, and when the picture was unveiled, the whole room applauded,” she says enthusiastically.

“It’s very, very exciting. And the fact that this is an image of the black hole at the center of our own galaxy makes it even more exciting,” says Daryl Haggard, a McGill University astrophysicist who is part of the EHT collaboration, where she contributes complementary observations using other instruments than radio telescopes.

The results presented on Thursday are “more than symbolic,” notes Jean-René Roy, a Quebec astrophysicist who has worked for several international observatories throughout his career. “We see more or less the same as with Messier 87*: It’s reassuring. This validates the analysis methods used,” he says.

The results of the EHT collaboration, which includes more than 300 scientists from 80 institutes around the world, are detailed in 6 scientific articles published in the journal on Thursday The Letters of the Astrophysical Journal.

snap merge

The gas trapped in the vortex of Sagittarius A* orbits very rapidly within a few minutes. In order to get a real image, the scientists had to eliminate high-frequency movements. The image revealed by the EHT collaboration is therefore a fusion of thousands of images digitally reconstructed from data collected during the observation sessions, each lasting several hours.

The result: a shadow surrounded by three “light nodes”. The environment of black holes is “extreme environment”, says Professor Hlavacek-Larrondo. We expect turbulence and structures. However, to ensure that these three knots are genuine features of Sagittarius A* and not an artifact of the measuring devices, additional analyzes are necessary, the expert warns.

Despite this, the diameter of the black hole’s shadow is exactly what was expected. Astronomers Reinhard Genzel and Andrea Ghez received the 2020 Nobel Prize in Physics for their very accurate calculation of the mass of the “compact object” at the center of the Milky Way (4.14 million times that of the Sun) from the motion of the surrounding stars, allowing the size can be deduced.

Analysis of the images from the EHT radio telescopes revealed that the black hole’s horizon is 50 microsecond arcs wide, equivalent to a diameter of 60 million kilometers. This is slightly larger than Mercury’s orbit around the Sun. “This too is a confirmation of general relativity, this time at the most extreme level,” says M.me Hlavacek-Larrondo.

In the coming years, further evaluations of the data collected in 2017, as well as further data obtained in 2018, 2021 and 2022, will make it possible to understand “the complex connections” between the forces and the matter that are articulated in the “ecosystem”. around our black hole, says Professor Haggard. A better understanding of the supermassive object’s magnetic field will likely be the next step to be taken.

A fruitful collaboration

To see in the video

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