Hawking was right (Einstein didn’t think they could happen).
It looks uncomfortably like the Eye of Sauron, but it’s actually the heart of M87, a giant elliptical galaxy findable in our skies in the constellation of Virgo. A team of Harvard astronomers used the Event Horizon Telescope (EHT, a collection of eight radio telescopes scattered across the globe) to produce the first ever image of a black hole.
The image shows a bright ring of glowing gasses swirling around a dark center that marks the event horizon of the black hole. The event horizon is the point at which gravity from the black hole is so intense that nothing – not even light – can escape.
The team was looking at one of two possible targets to produce the image. The first was the obvious one, the black hole at the center of the Milky Way galaxy, known as Sagittarius A* (pronounced Sagittarius A-star), and a second that lies at the heart of M87. In the end, they decided to concentrate on M87.
Here’s a microcosmic metaphor: Which is easier for you to photograph, a grain of corn across the room, or the one inside your own colon?
This amazing image is the result of a colossal, years-long effort by about 200 researchers. Weather conditions had to be just right, as all eight radio telescopes had to have clear skies to participate, and all eight were needed. After a couple of years of trying, finally in 2017 they got their chance. The array generated so much data that it was actually quicker and cheaper to FedEx the physical hard disks containing over 50 petabytes of data to Harvard University for final computational assembly, a process that took more than two years.
To help you wrap your brain around just how big this black hole is, here is a diagram showing the circumference of the event horizon. Superimposed on it is a little sketch (via XKCD) showing our sun, the orbit of Pluto, and how far the Voyager probe has gotten on its journey into interstellar space.
Capturing an image of a black hole, project leaders said, is about more than getting the first glimpse of one of the most curious objects in the cosmos. It also opens the door to allowing astronomers and physicists to test Einstein’s theories of gravity and general relativity under the most extreme conditions in the universe.
“A black hole, if you looked at it naked … would be invisible,” said Sheperd Doeleman, director of the EHT. “It’s nature’s most amazing invisibility cloak.”
So how do you take a picture of something from which even light cannot escape?
“In a paradox of its own gravity,” Doeleman explained, “you wind up seeing it because all the gas and dust that’s attracted to it gets crushed into a smaller and smaller volume, causing it to heat up to hundreds of billions of degrees. So you wind up with a 3-D flashlight illuminating all the space-time around the black hole.”
Disappointed in the lack of image resolution? Don’t be.
For one thing, it’s very tightly zoomed in. Most of the news outlets aren’t showing you the bigger picture, which is exactly how much of the M87 black hole’s local environment it’s actually devouring. Here’s an image from the Chandra X-Ray telescope that sheds some illumination on the matter, if you’ll pardon the expression.
Here’s something else rather remarkable: the image looks exactly as we expected it would. What a black hole should look like has been modeled extensively on supercomputers, and if you blur the image, you get pretty much exactly what the new EHT image shows.
Researchers used general relativistic magnetohydrodynamic (GRMHD) models for the accretion flow and synthetic images of these simulations produced by general relativistic radiative transfer calculations to compare them to the observation of the M87 black hole, and got some results that show that we see exactly what we expected to see.
The M87 black hole is tilted away from Earth, so we’re looking mostly at its bottom end. It’s spinning clockwise with reference to us at about half the speed of light, and it’s got a mass of 6.5 billion times that of our own home star. Now, with that size and mass in your head, have a look at this video clip – it’s about ten seconds worth of animation from the GRMHD simulation.
If that doesn’t give you a sense of the enormity of the accomplishment of the Harvard based team, nothing will.
They’re still working on imaging Sagittarius A*, so that’s still coming. Be patient. It’s a lot of data.
How Grad Student Katie Bouman Helped Make It Happen
The effort wouldn’t have been possible without Katie Bouman, who developed a crucial algorithm that helped devise imaging methods.Three years ago, Bouman led the creation of an algorithm that eventually helped capture this first-of-its-kind image: a supermassive black hole and its shadow at the center of a galaxy known as M87. She was then a graduate student in computer science and artificial intelligence at the Massachusetts Institute of Technology at the time. She worked out methodologies and techniques for interpolating data from the different sources and compiling them into a single image.
Her algorithm, and many others, helped fill in the gaps
That’s where Bouman’s algorithm — along with several others — came in. Using imaging algorithms like Bouman’s, researchers created three scripted code pipelines to piece together the picture.
“We developed ways to generate synthetic data and used different algorithms and tested blindly to see if we can recover an image,” she told CNN.”We didn’t want to just develop one algorithm. We wanted to develop many different algorithms that all have different assumptions built into them. If all of them recover the same general structure, then that builds your confidence.”
No matter which approach they used, all the images came out the same. “No matter what we did, you would have to bend over backwards crazy to get something that wasn’t this ring,” Bouman said.
This new observation signals a new age in human science and astronomy. We have seen the unseen, and things get interesting from here.