The new image produced by the Event Horizon Telescope (EHT) Collaboration shows the area close to the event horizon of Sagittarius A* (Sgr A*), the 4.3-million-solar-mass black hole at the center of our Milky Way Galaxy.

This is the first image of Sagittarius A*, the supermassive black hole at the center of our Milky Way Galaxy. Image credit: EHT Collaboration.

This is the first image of Sagittarius A*, the supermassive black hole at the center of our Milky Way Galaxy. Image credit: EHT Collaboration.

“We were stunned by how well the size of the ring agreed with predictions from Albert Einstein’s theory of general relativity,” said EHT project scientist Dr. Geoffrey Bower, an astronomer at the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.

“These unprecedented observations have greatly improved our understanding of what happens at the very center of our Galaxy, and offer new insights on how these giant black holes interact with their surroundings.”

To image Sgr A*, which is about 27,000 light-years away from Earth, the EHT team created the powerful Event Horizon Telescope, which linked together eight existing radio observatories across the planet to form a single Earth-sized virtual telescope.

It observed Sgr A* on multiple nights, collecting data for many hours in a row, similar to using a long exposure time on a camera.

The breakthrough follows the EHT Collaboration’s 2019 release of the first image of a black hole, called M87*, at the center of the giant elliptical galaxy Messier 87.

The two black holes look remarkably similar, even though Sgr A* is more than a thousand times smaller and less massive than M87*, which has a mass of 6.5 billion solar masses.

“We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar,” said Professor Sera Markoff, co-chair of the EHT Science Council and am astrophysicist at the University of Amsterdam.

“This tells us that general relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”

This achievement was considerably more difficult than for M87*, even though Sgr A* is much closer to Earth.

“The gas in the vicinity of the black holes moves at the same speed around both Sgr A* and M87*. But where gas takes days to weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in mere minutes,” said EHT scientist Chi-kwan Chan, an astronomer at Steward Observatory and the Department of Astronomy and the Data Science Institute at the University of Arizona.

“This means the brightness and pattern of the gas around Sgr A* was changing rapidly as the EHT Collaboration was observing it — a bit like trying to take a clear picture of a puppy quickly chasing its tail.”

The new EHT’s results appear today in a special issue of the Astrophysical Journal Letters.

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