Today, for the first time ever — we have an actual image taken of a black hole!
Specifically, the black hole at the centre of the Messier 87 (M87) galaxy which is 55 million light-years away from us. Everything you have seen previously were artistic impressions of what we thought black holes would look like. The astounding photo was taken by the Event Horizon Telescope (EHT), a network of eight radio telescopes including such varied locations as Antarctica and Spain. More than two-hundred scientists were involved in this massive scientific effort.
So what am I looking at?
You are looking at the accretion disk (gas, dust and other material in space that has come close to a black hole but not quite close enough to be sucked into it) of a black hole with a mass of 6.5 billion times that of our own sun. The black hole itself is essentially invisible to us because nothing, not even light, can escape the gravitational field created by it. Thus, the dark circular shape you see in the image is the black hole, as well as something called the event horizon. The event horizon defines the area around the black hole from which no light or matter can escape. This is why the circular shape shown is not the black hole alone but rather the black hole and its generated event horizon.
How was the image taken?
The image was taken by 8 radio telescopes here on Earth using something called Very-long-baseline-interferometry which basically creates a virtual telescope about the same size as the Earth. Because these are radio telescopes and not optical telescopes, we are actually looking at the radiation emitted by the material surrounding the black hole (the brighter the colour, the more emitted radiation) and not an actual optical photograph. This is incredibly useful as it allows us to “see” the material around the black hole from much farther away than with an optical telescope . These telescopes generated astonishingly large amounts of data (5,000 trillion bytes worth!) and it took two weeks to compile all the information generated into the image we now have using supercomputers.
Is this what was expected?