The incredible story behind the first image of a black hole

A black hole is invisible by nature. One of the strangest predictions to come out of Albert Einstein's theory of general relativity, a black hole emits no radiation we can detect, and it swallows up everything that falls on it, matter and light alike. So it might seem paradoxical to talk about capturing an image of a black hole, but this is precisely the mission of the Event Horizon Telescope (EHT). Today, April 10, 2019, will go down in history as the day EHT scientists released the very first direct image of a black hole. It's not one in our own Galactic centre, but is at the centre of the galaxy M87 – a resident of the neighbouring Virgo galaxy cluster, which is the home of several trillion stars. The feat marks the first time in history that astronomers have seen the shape of an event horizon. It's an unprecedented map of gravity at its strongest, involving hundreds of astronomers, engineers, and data scientists from around the world."This is truly something no one has ever seen before and we actually didn't ever imagine it would be possible," says Priyamvada Natarajan, an astronomer at Yale University. She is not part of the EHT collaboration, but studies how supermassive black holes are born and evolve. "It's something that moved from the realm of the imagination to the real."Astronomers believe that nearly every large galaxy, including our Milky Way, contains a supermassive black hole at its centre. The M87 black hole weighs in at 6.5 billion times the mass of the Sun, making it one of the larger supermassive black holes known. The EHT image shows the glowing plasma — matter where electrons have been stripped from their atoms by the intense friction — surrounding the black hole, with the "shadow" at the centre revealing the shape and size of the event horizon itself.In a very real sense, the gravitational influence of a black hole is the way we can see it, and that's precisely what the EHT image reveals. The asymmetrical shape of the matter shows both the way plasma swirls around the event horizon, and also how the gravitational distortion of spacetime affects the path of the light emitted by the material. The M87 event horizon shape is precisely in agreement with the predictions of general relativity, including an estimate of how rapidly the black hole is rotating.The theory of black holes, including the nature of real astronomical black holes, was developed by a large number of researchers over the past century. In 2000, astronomer Dimitrios Psaltis of the University of Arizona and his team calculated how to see the event horizon of a black hole. Today, he's one of the leaders of the theoretical side of the EHT - and says that the image is an amazing proof that Einstein was right.The implications of this image go beyond testing general relativity, though. "A black hole collects matter and grows by eating that matter up," says Becky Smethurst, an astronomer at Oxford University. Sometimes the pressures get so great around the black hole that it can throw out material in a wind before it gets to the event horizon – and the energy that it expels affects the galaxy as a whole. In other words, what happens at the event horizon can influence what atoms get distributed throughout an entire galaxy. That includes the types of atoms responsible for life as we know it on Earth, meaning black holes may even have a role in our own existence."Even though I'm interested in what happens on the big scale, it all comes down to what's happening at the very small scale," Smethurst says.Imaging that small scale presents many challenges. Despite its huge mass, M87's black hole could fit inside the Solar System; since the galaxy is 53.5 million light-years away, astronomers need a very large number of telescopes to observe it, detecting radiation with wavelength of 1.3 mm. And they need a lot of computer storage which thankfully has become cheap enough to allow EHT data scientists to purchase petabyte-size disks for the huge amounts of data from each telescope.The initial phase of EHT in 2017 consisted of eight observatories acting in concert, forming a worldwide array of telescopes with enough power for the first time in history to see light emitted right from the edge of a black hole. These telescopes are located in the US (both the mainland and Hawaii), Europe, Chile, and Antarctica. The EHT has also been observing Sagittarius A*, the supermassive black hole at the centre of the Milky Way. However, our galaxy is much 'messier' than M87 - meaning there is much more gas and dust that obscure the picture. The collaboration is still processing how to mitigate the effects of the matter lying between the Solar System and the Galactic centre. To help with that process, four more observatories are now joining the EHT."When Apollo [8] turned and took a picture of the Earth, we had this wonderful moment of seeing a picture that had not been seen before," Psaltis says, adding that the first image of a black hole might carry a similar emotional weight. "It's something that inspires and excites us."Natarajan agrees. "Black holes have this incredible gravitational pull for us. It's amazing that one happens to be alive at a time right when we're learning so much about black holes."More great stories from WIRED– The Play Store is packed with nasty, violent games for kids– Why does the London Tube still not have Wi-Fi in tunnels?– Netflix's Love, Death & Robots is just tedious sexist sci-fi– The grim reality of life under London's Gangs Matrix– Care about online privacy? Then change your phone number Get WIRED Weekender, your at-a-glance roundup of the most important, interesting and unusual stories from the past week. In your inbox every Saturday by 10am. by entering your email address, you agree to our privacy policy Thank You. You have successfully subscribed to our newsletter. You will hear from us shortly. Sorry, you have entered an invalid email. Please refresh and try again.