Astronomers from the Event Horizon Telescope Collaboration have today revealed the first image of the supermassive black hole at the center of the Milky Way galaxy, produced using a network of radio telescopes around the world.
The Event Horizon Telescope Consortium was formed in 2015, and essentially linked together existing radio telescopes from around the globe to form a powerful single observatory.
The combined efforts of ALMA and APEX in Chile, IRAM in Spain, the South Pole Telescope, the LMT in Mexico and the JCMT, SMA and SMT in the US resulted in the first observations being made in April 2017, with data analyzed using dedicated supercomputers at the Max Planck Institute for Radio Astronomy in Bonn, Germany, and the Haystack Observatory in Haystack, Massachusetts.
The first direct images of a black hole at the center of the Messier 87 galaxy were subsequently released two years later, closely following black hole features predicted in Albert Einstein's theory of general relativity and potentially proving the existence of event horizon features theorized around black holes.
The EHT Consortium has added more observatories to the array since then – in the French Alps, Greenland and the US – and has undertaken further observation campaigns in 2018, 2021 and this year.
The EHT research team, which is made up of more than 300 researchers from around the world, says that it's long been suspected that there's a black hole at the center of our galaxy, and now the first image of that massive object has been revealed.
The image of Sagittarius A* shows a ring of glowing gas surrounding a dark central region – or shadow – and captures light bent by the object's immense gravity, plus it's reported to be the first direct visual evidence that Sgr A* is indeed a black hole.
The image comes from observations of Sgr A* made over multiple nights in 2017 by the eight radio telescopes of the original EHT configuration, and is notably similar to the image of the M87* black hole released in 2019, though Sgr A* is reckoned to be a thousand times smaller and less massive.
"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 Co-Chair of the EHT Science Council and professor of theoretical astrophysics at the University of Amsterdam, Sera Markoff. "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."
Because the gases around Sgr A* move much more quickly than those around M87*, the released image is actually an average of different images extracted by the researchers.
"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*," explained EHT scientist Chi-kwan Chan. "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* were 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."
Scientists will now study the differences between the two different-sized black holes, and use the new data to test theories and generate models on how gases behave around supermassive black holes.
The EHT team's results have been published in special edition of The Astrophysical Journal Letters.
The video below zooms into Sgr A*.
Source: European Southern Observatory
