First image emerges of black hole at the centre of the Milky Way galaxy

ASTRONOMERS have released the first-ever image of Sagittarius A* – a black hole at the centre of the Milky Way galaxy.

On Thursday, May 12, astronomers unveiled the first image of the supermassive black hole at the centre of our own Milky Way galaxy, produced by a global research team called the Event Horizon Telescope (EHT) Collaboration using observations from a worldwide network of radio telescopes.

As noted by the EHT, this result provides “overwhelming evidence that the object is indeed a black hole and yields valuable clues about the workings of such giants, which are thought to reside at the centre of most galaxies.”

“We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity,” said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.

“These unprecedented observations have greatly improved our understanding of what happens at the very centre of our galaxy, and offer new insights on how these giant black holes interact with their surroundings.” The EHT team’s results are being published today in a special issue of The Astrophysical Journal Letters.

The eagerly-anticipated picture of Sagittarius A* – which is roughly 4.3 million times the mass of our sun and is located about 27,000 light-years away from the Earth.

“Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a telltale signature: a dark central region (called a “shadow”) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun,” EHT said via a blog post.

The breakthrough follows the EHT collaboration’s 2019 release of the first image of a black hole, called M87*, at the centre of the more distant Messier 87 galaxy.

EHT note that the two black holes look remarkably similar, even though “our galaxy’s black hole is more than a thousand times smaller and less massive than M87*.”

“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,” says Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands.

“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 us.

EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, US, explains: “The gas in the vicinity of the black holes moves at the same speed — nearly as fast as light — 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.

“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.”

Around 300 researchers from 80 institutes around the world came together over a five year period to develop sophisticated new tools that accounted for the gas movement around Sgr A* and while M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for Sgr A*.

The image of the Sgr A* black hole is an average of the different images the team extracted, finally revealing the giant lurking at the centre of our galaxy for the first time.

“Now we can study the differences between these two supermassive black holes to gain valuable new clues about how this important process works,” said EHT scientist Keiichi Asada from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei.

“We have images for two black holes — one at the large end and one at the small end of supermassive black holes in the Universe — so we can go a lot further in testing how gravity behaves in these extreme environments than ever before.”

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