“We have been studying black holes for so long that sometimes it’s easy to forget that none of us has seen one. This will leave an imprint on people’s memories.” Those were the words of France Córdova, director of the US National Science Foundation as she chaired the press briefing that unveiled the image of the black hole.
The image obtained has since become iconic – finding its way across social media platforms, news networks and more. While it is not an image of the black hole itself, it is an image of a black hole’s accretion disc, a ring of gas and dust that steadily “feeds” the monster within. The black hole itself cannot be photographed because nothing escapes the gravitational pull of the black hole – not even light.
The breakthrough image was captured by the Event Horizon Telescope (EHT), an array of eight radio telescopes with more than 200 scientists working on them. The EHT was able to trace the outline of a massive black hole in the Messier 87 galaxy – about 55 million light years away from the earth. The EHT picked up radiation emitted by particles within the disc which experience extremely hot temperatures and are in constant motion at close to the speed of light before they disappear down the black hole.
The existence of black holes has been postulated by Albert Einstein in his theory of relativity, despite his own scepticism about their existence. However, since those days, increasing evidence has pointed toward their presence in space. The EHT focused their attentions on two particular black holes – one within the Milky Way galaxy (called Sagittarius A) and the other one on Messier 87. M87 was the one which yielded and scientists are hopeful of getting an image from Sagittarius A at some point in the near future.
Capturing the image also required a lot of patience as there needed to be perfect weather conditions across all the sites involved in the project. Hydrogen masers, which are atomic clocks, coordinated the observations from the eight sites, and the resultant data generated filled up to half a tonne of hard drives. And they have already led to some interesting observations about an environment whose gravitational pull is so fierce that reality is different and distorted from what we normally know it to be. At the event horizon, light is bent in a perfect loop around the black hole. Einstein’s theory also predicted a rounded shape of the black hole’s halo – something that the EHT findings have corroborated.
The one obstacle that they may however, not be able to overcome is finding out what is inside the black hole itself. That, according to Heino Falcke, chair of the EHT science council, who is based at Radboud University in the Netherlands, may be a step too far. He says, “The big question for me is whether we’ll ever be able to transcend that limit. The answer may be maybe not. That’s frustrating but we’ll have to accept it.”
The EHT is based on a key algorithm devised by former MIT student Katie Bouman. Katie, a computer scientist currently at CalTech, developed an algorithm while studying at the famous Cambridge institution that allowed combining the data from the eight different locations as well as filtering out any confounding factors such as atmospheric humidity for example, in order to generate a comprehensive single image. After rigorous testing, Bouman’s algorithm eventually played a key role in allowing us to get closer to seeing something whose existence has been known for some time but never actually been seen.