First glimpse of supermassive black hole at the centre of our galaxy.

Written by Hannah Mahon

Astronomers have captured the first image of a supermassive black hole in our galaxy, helping solve the mysteries of black holes.

On May 12, 2022, astronomers announced they had assembled the first image of a supermassive black hole, located at the centre of our galaxy, the Milky Way. The image points to clues about the workings of such giants and could reveal secrets of the cosmos that shape our galaxy.

The unveiling of the long-anticipated image was only accomplished after two years of hard work. The image captured by NASA’s Event Horizon Telescope (EHT) project was part of a global collaboration of more than 200 scientists. The EHT is made of a network of eight linked telescopes which rely on widely spaced antennas from all over the world, thus acting as one giant telescope.

“From the technology perspective it’s mind-blowing that we can do this,” Prof. Carole Mundell, an astrophysicist at the University of Bath commented on the latest image.

The black hole is Known as Sagittarius A* (or Sag A* for short), which is the closest of its kind to Earth and can be seen by the human eye in the Sagittarius constellation. It is approximately 27,000 light-years away from Earth and has an estimated mass of millions times that of our Sun. Experts say that due to its distance from Earth, it appears the same size in the sky as a doughnut on the moon.

The EHT is made of a network of eight linked telescopes which rely on widely spaced antennas from all over the world, thus acting as one giant telescope.

The image was captured by using observations of light. Matter that is dragged towards the centre of Sag A* is heated up, emitting light, giving scientists a view of the ‘shadow’ of Sag A*. Despite not being able to see the black hole itself, the dark region surrounded by a bright ring-like structure were tell-tale signs of a black hole. The glowing gas encircling the black hole in a bright ring of bending light is known as the accretion disk.

Supermassive black holes are regions of the spacetime continuum where the gravity is so strong nothing can escape it, not even light or particles. Before taking this image, black holes were observed through indirect evidence such as bursts of radiation and gamma rays and the study of their effects on other planetary bodies.

To the untrained eye Sag A* can often be confused with the black hole Messier 87, according to the EHT team, when in reality the two objects are very different. Sag A* consumes a small amount of material which differs from the usual assumption that black holes are violent ravenous monsters. In contrast, Messier 87 is one of the largest black holes in the universe and its powerful, large jets launch light and matter from its poles to outer space. Both black holes behaved as predicted by Einstein’s theory of General Relativity, which holds that the force of gravity arises from the curvature of space and time.

The latest observations show that Sag A*’s angle of rotation is not aligned with the galactic plane and is off by 30 degrees. In addition, hints of magnetic activity similar to that in the Sun’s atmosphere have been seen.

Although there is still a great deal to learn about Sag A*, the unveiling of the image has helped develop the understanding of black holes. It has enabled scientists to calculate the mass of a black hole more directly and supplied hints to how black holes unleash huge jets of particles travelling near the speed of light.    

Hannah Mahon is a third year Physics with Space Science student with a passion for communicating science to the public. You can find her on Linkedin here

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