Monster black hole snapped
An international team of astronomers (space scientists) have released the first ever image of the monster at the centre of our Milky Way galaxy. This strange object, known as Sagittarius A* (pronounced “Ay-star”), is named after the star constellation where it can be found. It is about 20 times wider than the
Sun, but four million times heavier.
Astronomers call objects like Sagittarius A* supermassive black holes. They are thought to lie at the centre of most galaxies, and pull powerfully on everything around them. Clouds of gas and dust, space rocks and even stars that stray too close to supermassive black holes are torn apart. Not even light – the fastest thing in the universe – can escape if it gets too close to a point of no-return called the event horizon. This means that from the outside, Sagittarius A* looks pitch black.
How have scientists made an image of something that doesn’t emit any light? Astronomers from the Event Horizon Telescope project instead looked for its shadow. Light coming from objects behind and near the black hole has been warped, creating a bright ring with the shadow of the black hole in the middle.
The centre of our galaxy is so far away that this light takes 27,000 years to reach Earth. This means that the region around Sagittarius A* is a tiny target as viewed from Earth. What’s more, it is hidden behind clouds of stars and dust that are impossible for normal light to pass through.
However, radio waves emitted by gas clouds around the black hole can pass through unaffected. Astronomers use enormous metal dishes called radio telescopes to detect these waves. However, because radio waves are much bigger than light waves, individual telescopes can only produce very blurry images. To see enough detail to spot the shadow of Sagittarius A*, the team linked up eight radio telescopes around the world to make a single, super-sized radio telescope.
The final image is a result of combining thousands of separate images using computer programs, but it still appears blurry. That’s because the gas around the black hole is moving so fast that its brighter areas change between one image and the next.