Abandon all hope, ye who enter here: scientists have presented the first-ever image of a black hole.
The image shows the shadow of the black hole at the centre of the galaxy M87, a massive galaxy in the Virgo galaxy cluster 55 million light-years away. Its mass is 6.5 billion times that of the Sun. It took a worldwide collaboration of telescopes, the Event Horizon Telescope (EHT), in order to find it. Scientists released their results at a press conference today.
“Black holes are the most mysterious objects in the universe,” Harvard astronomer and EHT director Shep Doeleman told Gizmodo.
Black holes have long served as a theoretical exercise. But astronomical observations in the past 60 years have increasingly demonstrated that there are objects in the Universe whose gravitational field is so intense that it warps spacetime such that light cannot escape beyond a point of no return, called the event horizon. Thanks to a world-side collaboration, is the closest image ever taken to the event horizon itself, near-direct evidence of the black hole’s existence.
This is not really a “picture” of a black hole, and the shadow does not denote the black hole’s event horizon. Instead, you’re seeing the effects of gravity on the radio waves emitted from matter surrounding the black hole in a slightly larger region around the black hole’s event horizon. Gravity warps the shape of spacetime itself, deflecting some of the light in the region and generating an eerie circular shadow.
But it’s a groundbreaking observation, and another important proof of the theory of gravity that physicists use as a guide to the universe, Albert Einstein’s theory of general relativity.
The Event Horizon Telescope’s scientists captured this image thanks to the principle of very long baseline interferometry, or VLBI. The resolution of a telescope relies on two main properties: the diameter of the light-collecting region and the wavelength of the light. You can’t alter the second part, and there’s sort of a maximum sensible limit to how large a satellite dish you can build. Instead, scientists combine data from a lot of different pairs of telescopes, called baselines. Eight telescopes were involved in creating this image, from the South Pole to Chile to Spain to the United States.
The telescope set out to image both the black hole at the centre of our own galaxy, as well as that of M87. Today’s results present those from M87 – an incredibly interesting object to study on its own as it is the center of an active galactic nucleus, one that spews jets. We now know that a black hole, and not some other compact object, is responsible for generating these jets, Avery Broderick, Associate Faculty at the Perimeter Institute and physicist at the University of Waterloo, explained during the press conference.
“Science fiction becomes science fact,” Broderick said.
But it’s important to note that interferometry still requires some work from people to create the image. We only capture some of the data; the EHT scientists explain that it’s sort of like playing a song with only some of the notes. With some special data-processing programs, they’re able to figure out what they were looking at based on the data they received.
Black holes as a theory are a consequence of trying to solve the equations of Albert Einstein’s theory of general relativity for a spherical, non-rotating system. However, it was the work of physicist David Ritz Finkelstein in 1958 that determined what black holes would look like in space: points of no return for light. We already had lots of indirect evidence of black holes’ existence – we’ve seen gravitational waves, predicted perfectly by mass turned into energy after the utterly inconceivable collision between a pair of black holes each a few dozen times the mass of the Sun. We’ve seen jets of particles spew forth from galactic centres that are far more energetic than those that come from collisions at our highest-energy physics experiment, the Large Hadron Collider. Technically, the EHT data is indirect evidence as well, but it’s about as close to direct evidence as we’ve had thus far.
It’s an amazing accomplishment. “The event horizon in black holes represent the limits of our knowledge,” Yale physicist Priyamvada Natarajan told Gizmodo.
“Omfg,” Harvard & Smithsonian astrophysicist Center for Astrophysics physicist Grant Tremblay told Gizmodo in a twitter direct message. “They actually see a shadow. Impossible to overstate how extraordinary that is.”
There’s a tonne of science left to do, and several papers have already come from the EHT data. The image immediately proves several ideas from Einstein’s theory of general relativity. But there are more questions – and we’ll keep you updated as the story unfolds.
Said Tremblay: “The image marks the start of a new epoch.”