In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyse their data, all while compiling an unprecedented library of simulated black holes to compare with the observations. The effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. 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. While M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for Sgr A*. The researchers had to develop sophisticated new tools that accounted for the gas movement around Sgr A*. 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.” 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. 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*. This achievement was considerably more difficult than for M87*, even though Sgr A* is much closer to us. "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.”
"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. 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*. 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. The EHT observed Sgr A* on multiple nights, collecting data for many hours in a row, similar to using a long exposure time on a camera. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. "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.īecause the black hole is about 27,000 light-years away from Earth, it appears to us to have about the same size in the sky as a donut on the Moon.
“ 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. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. This strongly suggested that this object - known as Sagittarius A* (Sgr A*, pronounced "sadge-ay-star") - is a black hole, and today’s image provides the first direct visual evidence of it.Īlthough 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. Scientists had previously seen stars orbiting around something invisible, compact, and very massive at the centre of the Milky Way. The image is a long-anticipated look at the massive object that sits at the very centre of our galaxy. The image was produced by a global research team called the Event Horizon Telescope (EHT) Collaboration, using observations from a worldwide network of radio telescopes. 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. Astronomers have unveiled the first image of the supermassive black hole at the centre of our own Milky Way galaxy.
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