First image of Sagittarius A*, the black hole in the centre of the Milky Way. Image: EHT Collaboration
There is now visual proof of a supermassive black hole in the centre of the Milky Way, which had been only been predicted until now.
Scientists have for the first time revealed an image of the black hole in the centre of our galaxy.
Taken with the help of hundreds of scientists and multiple telescopes across the world, the image is the first visual evidence confirming the presence of a supermassive black hole, known as Sagittarius A* or Sgr A* (pronounced sadge-ay-star), in the centre of the Milky Way.
The European Southern Observatory (ESO) headquarters in Garching, Germany, was one of the multiple locations where the image was revealed today (12 May).
The ESO, of which Ireland is a part, is partially responsible for the telescopes used by the Event Horizon Telescope (EHT) Collaboration, the global research team that led the effort to capture the first ever glimpse of our galactic centre.
Because a black hole is completely dark, it is impossible to actually see it – even in an image. However, the image released today reveals the telltale signs.
In the image, a dark central region called a shadow is surrounded by a bright ring-like structure. Because of the black hole’s incredible mass – 4m times that of our sun – light surrounding the object bends under the influence of its powerful gravity.
Until now, astronomers studying the centre of our galaxy had only been able to conjecture the presence of a black hole based on observations of stars orbiting around something invisible, compact and very massive. This prediction goes all the way back to Albert Einstein’s work around relativity.
“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.
“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 team’s results were published today in a special issue of The Astrophysical Journal Letters.
This is not the first time scientists have been able to capture an image of a black hole, however. In 2019, the ESO and EHT revealed the first-ever photo of a black hole – from a different galaxy, far, far away.
The image was from the centre of a galaxy called M87 which is approximately 55m light years away from Earth – meaning that if we travelled at the speed of light in that direction, it would take us 55m years to reach it.
Even though Sagittarius A* is at the centre of our galaxy, it is still 27,000 light years away from the Earth. Adding to the complexity of viewing the black hole is the high density of stars between the Earth and itself.
“Although many black holes are known in our galaxy, the one in the galactic centre is hundreds of thousands of times more massive again,” said Prof Paul Callanan of the University College Cork Department of Physics, who is involved with the ESO.
Callanan said that imaging such an object in the heart of our galaxy is an important step in our understanding of supermassive black holes, and how they interact with their environment and affect the evolution of galaxies.
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