We have peered into the abyss for the very first time. The Event Horizon Telescope (EHT), which uses a network of telescopes around the globe to turn all of Earth into an enormous radio telescope, has taken the first direct image of a black hole.
The light that makes up the image is not coming from the black hole – black holes do not emit any light, hence the name. Instead, the image shows the black hole’s silhouette against a background of hot, glowing matter that is being inexorably pulled in by its powerful gravity.
In 2017, the eight telescopes of the EHT collaboration observed two supermassive black holes: the one at the centre of our galaxy, which is called Sagittarius A*, and the much larger behemoth at the centre of another galaxy called M87.
This image shows the black hole in M87, which is 55 million light years away. “We’re looking at a region that we’ve never looked at before, a region that we cannot really imagine being there,” said EHT scientist Heino Falcke in a press conference today in Brussels. “It feels like looking at the gates of hell, the end of space and time.”
M87 is easier to observe because, while it is much farther away than Sagittarius A*, it is also much bigger and has less material swirling around it. The image may be blurry, but it is an incredible technical feat requiring observations all over the world with the very best radio telescopes.
“We’ve repurposed the entire Earth as a radio dish, it doesn’t get better than that unless we put something on the moon,” says Natarajan. “We are at the limits of our equipment and what we can do.”
The ring of light around the black hole looks a little lopsided, which is as expected. This comes from a prediction of Albert Einstein’s theory of general relativity, that the powerful gravitational pull of a black hole will actually bend light around it, making the light skimming the side of the black hole that’s rotating towards us appear brighter than the light on the side that’s spinning away.
Images of the event horizon are particularly important when it comes to testing general relativity, which governs the behaviour of gravity and very large objects. We know that it does not mesh with theories of quantum mechanics, which describes the very small, and the very edge of a supermassive black hole, where gravity is more intense than anywhere else we know of, is the best place to stress test that disconnect.
And this is the first direct evidence that event horizons are actually real. “The event horizon is very tantalizing because once something passes the event horizon it seems like we can’t know anything about it,” says Natarajan. “It is the limit of what is known and what is unknowable.”
This first image is pushing back the limits of our knowledge. “We have been studying black holes for so long that sometimes it is easy to forget that none of us has ever actually seen one,” said France Córdova, the director of the National Science Foundation, at a press conference in Washington, DC. That is, none of us has seen one until now.