Astronomers have unveiled the first image of the supermassive black hole at the center of the Milky Way galaxy. It was theorized there was a black hole at the center of the galaxy but this image provides overwhelming evidence that this is the case.
The National Science Foundation (NSF) says that this is a long-anticipated look at the massive object at the center of the Milky Way Galaxy, the galaxy in which Earth’s Sol System resides. The NSF says that scientists had previously seen stars orbiting around something massive, compact, but invisible at the galaxy’s center which strongly suggested a black hole.
This image is the first direct visual evidence that the object, known as Sagittarius A* (Sgr A*), is indeed a supermassive black hole.
As is the case with a previous image of black holes — which was also captured with EHT in 2019 — the image does not actually show the black hole itself since it is completely dark. Black holes absorb all light, but the glowing gas around the hole reveals a telltale signature of the object: a dark central region (which the NSF says is called a “shadow”) surrounded by a bright ring-like structure. The gravity of this hole is estimated to be four million times more massive than the Sun.
“We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity,” EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, says.
“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.”
How the Image Was Captured
The black hole is about 27,000 light-years away from Earth and in order to image it, scientists created the EHT which links eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope, the NSF explains. The EHT was tasked with observing Sgr A* over multiple nights and collected hours of concurrent data, which the NSF says is similar in principle to using a long exposure on a standard camera.
Capturing this image was considered significantly more difficult than the one that was taken of black hole M87* in 2019 even though Sgr A* is much closer.
“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*,” EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, U.S., explains.
“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.”
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The NSF says that the researchers had to develop new tools to account for that gas movement, while M87* was a lot easier because it was steadier and all the images that were captured looked almost the same. In contrast, the image of the Sgr A* black hole is an average of the different images the team extracted.
“Now we can study the differences between these two supermassive black holes to gain valuable new clues about how this important process works,” EHT scientist Keiichi Asada from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, says.
“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.”
The EHT team’s full results are being published in a special issue of The Astrophysical Journal Letters today.
Image credits: Event Horizon Telescope collaboration