The existence of black holes, first proposed by Albert Einstein in his 1916 general theory of relativity, has been known for decades. However, astrophysicists have thus far relied on indirect evidence, such as the stars orbiting a large and invisible object in the centre of the Milky Way, to prove their presence. That changed on April 10, 2019, with the release of the first-ever direct visual evidence of a black hole in the centre of the galaxy M87, located 55 million light-years from Earth.
The culmination of many years of hard work and collaboration by an international team of more than 200 astrophysicists, the image does not show the black hole itself. That's because, as the name suggests, they are black, and hence, invisible against the backdrop of space. Instead, the scientists used radio signals to capture the black hole's “shadow” — the bright ring that forms around its boundary, or “event horizon,” where light bends due to the hole's extreme gravitational forces.
“We now have visual evidence for a black hole,” Event Horizon Telescope project director Sheperd Doeleman told reporters at a press conference in Washington, DC. “It is also consistent, the shape of this shadow ... with Einstein's predictions.”