Humanity has had its first ever peek at a black hole.
The blazing image of a red and yellow circle is the first anyone has seen of the phenomenon. As well as giving an unprecedented view of one of the most powerful and mysterious things in the universe, it also helps develop our understanding of the fundamental forces that shape space.
Scientists will be examining what exactly all the findings from this photo mean for years to come. And they expect to go on to discover even more, as they use the same techniques on other sources inside other galaxies.
But the image has delighted the world. And it has also left some people more than a little confused about what exactly it shows and how it was taken.
Here’s everything you need to know about the breakthrough discovery.
1. Why has it taken so long to get this picture?
2. What is a black hole?
3. Why does this one look like that? Why is it so grainy?
4. What does this mean for our understanding of space?
5. What do we do now?
Why has it taken so long to get this picture?
The work that allowed this photo to be taken has been going on for decades. It meant overcoming difficulties that have seemed impossible.
“We have seen what we thought was unseeable,” says astrophysicist Sheperd Doeleman, director of the Event Horizon Telescope at the Centre for Astrophysics, Harvard and Smithsonian. “We have seen and taken a picture of a black hole. Here it is.”
The central difficulty with trying to get pictures of black holes is given away in their name: they are black because they have such a strong gravitational pull that light falls into them and can’t escape. As such, it can’t get to here and we can’t take a photograph of it.
What’s more, the area between us and the black hole itself is blocked up by all sorts of other objects: everything from stars to the humdrum weather down here on Earth. Taking the picture required scientists “to have the perfect weather all across the world and literally all the stars had to align”, notes Jessica Dempsey, a co-discoverer and deputy director of the East Asian Observatory in Hawaii.
To get through all of that difficulty, astronomers had to work to join eight different dishes up into one huge virtual telescope, allowing them to work together and see further than they would individually. That happened in April 2017 – scientists have been working to pick through the results in the years since.
They were synchronised together using a technique called very-long-baseline interferometry or VLBI. It allowed the astronomers to achieve a level of angular resolution equivalent to reading a newspaper in New York from a pavement cafe in Paris.
Even then, the details were sketchy: they had to look through all the data received to ensure that they were seeing what they thought they were. That required complex analysis of the data using algorithms as well as scientific understanding, to allow them to fill in the gaps in the grainy and unclear images and produce the one that flew around the world on Wednesday.
What is a black hole?
Black holes are made when massive stars die and then collapse. The matter is crushed down into an infinitely small space, and very odd things start to happen to physics, space and time.
Because they are so dense, the gravitational force they exert on the things around them causes physics to work in strange ways. It means, for instance, that they tug light into them.
But around their edges is an “event horizon”, marking the border of where their pull allows light to escape. That’s an important part of the black hole and it’s what we see in the new picture.
People often assume that falling into a black hole would mean you’d be torn to bits. But this one is so incredibly huge, say scientists, that the strange forces it exerts mean that you could fall into it and make it through.
You’d never hear from that person again, however, and it’s not entirely clear where they’d end up.
Why does this one look like that? Why is it so grainy?
We should consider ourselves blessed to be able to see even this quality of picture, but some people noted that it looked a little blurry.
That is probably partly because we have so much to compare it to, in the form of illustrations of black holes in the past. Those are often released to accompany stories about black holes, and they are almost always dramatic – but the people creating them are not hit by the same limitations outlined above, and don’t have to deal with actually taking a picture.
The various techniques required to really see the black hole – including looking at the black hole using radio waves – mean that the detail is relatively limited.
It might also look quite small in the picture. But perhaps the radio telescope is slimming or it’s just because it’s very far away: the black hole is huge, the size of 6 million of our suns.
What does this mean for our understanding of space?
It mostly means that we were right. Scientists say they were surprised to be so unsurprised by what they found, and how much it aligned with their expectations of black holes and about Einstein’s theory of general relativity.
One of the important reasons to spend so much effort taking this photo is that it helps us understand how the event horizon works and so how that lines up with our theoretical work on black holes.
“We have achieved something presumed to be impossible just a generation ago,” says Doeleman.
He says the research “verifies Einstein’s theory of gravity in this most extreme laboratory.”
What are we going to do now?
That doesn’t mean all the science is done. In fact, it’s just beginning: researchers now have plenty of work to do looking at the data from these pictures, as well as hoping to harvest some more.
All of the data from the current work will be released in the coming days to allow scientists to look through it. They will be searching for more discoveries, of course, but they will also work to check the current claims: at this level of innovation, nothing is certain and the researchers behind the work admit that other interpretations may be possible.
Another potential black hole had been expected to have its photo taken and released, too: the source known as Sagittarius A*. Some had suggested that it could be even more spectacular.
But researchers said the early results from M87 were so impressive and exciting that they opted instead to focus on that one. More might come from the other source in the future.
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