Black holes are some of the most intriguing and mysterious objects in the universe, inspiring entire libraries of both scientific research and science fiction, from Einstein to the movie Interstellar. Yet despite the hold their inconceivable gravity has on our imaginations, as well as our understanding of physics, humans have never actually seen a black hole.
That appears set to change Wednesday with the impending release of the first image taken of Sagittarius A*, the black hole at the center of our Milky Way galaxy. (Editors' note, April 10: As it turned out, the black hole image that astronomers released was of the object at the center of the Messier 57 galaxy. They're still processing the data on Sagittarius A*.)
It's a landmark moment for both science and technology made possible by the Event Horizon Telescope, which is actually an array of telescopes spread out across the Earth. You watch it here.
Yes, I know what you're thinking: "I've seen plenty of pictures of black holes."
Perhaps you're thinking of something like this:
All these images we've seen from NASA and other scientific organizations are just illustrations created with the help of artists, although many of them are actually based on data from real telescopes. The above one comes largely from data gathered by NASA's Chandra X-Ray telescope, which is able to detect the super-heated matter being pulled toward the event horizon, or perimeter of a black hole.
So that beautiful illustration is kind of like drawing a hurricane based on wind speed data from the outer edges of the storm. To actually see a satellite image of a brooding and sprawling tropical cyclone is another thing altogether.
But to really capture a direct image of a black hole, or at least the shadow of one outlined by the bright material being pulled toward it, requires some serious collaborative engineering.
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Here a telescope, there a telescope
The EHT is actually an array of radio telescopes on different sides of the globe that are linked to create what's called a Very Long Baseline Interferometer (VLBI) the size of the Earth itself. The basic idea here is that radio telescopes in different locations are combining their signals to boost their power.
If you've seen pictures of the Very Large Array in New Mexico (featured prominently in the 1997 movie Contact) with its multiple telescopic dishes all working together, then you can visualize the concept: Just imagine Jodie Foster tapping into an array of dishes that are separated not by meters but by thousands of miles instead.
This planet-sized observatory is necessary because, as the Smithsonian Astrophysical Observatory explains in the below animation, while Sagittarius A is 4 million times as massive as our sun, it's still really far away -- a distance of about 26,000 light years.
This is, of course, good news for all people interested in not getting sucked into a black hole, but it makes the thing very hard to photograph; it would be comparable to trying to see the dimples on a golf ball in Los Angeles... from New York. Better get out your super zoom lens, which is also kind of what the Event Horizon Telescope is.
The EHT's array of observatories includes telescopes in Chile, Hawaii, Arizona, Mexico, Spain and the South Pole, all precisely synchronized to collect several petabytes of data, all of it combined with the help of a supercomputer to create the first image of Sagittarius A.
The image we expect to see Wednesday comes from data that was actually collected back in 2017. Part of the reason for the delay is that while we've become much better at processing huge amounts of data in recent years, the internet still isn't quite quick enough to zap petabytes' worth of information around the world on demand. Each EHT location stored its observation data on a physical hard disk that had to be transported to a data-processing center and combined with data from the other observatories.
So now we have a phalanx of scientists excited about looking at a black hole on the other side of the galaxy -- it's no exaggeration to say that the entire universe is at stake here... or at least our fundamental understanding of the universe.
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Proving Einstein right
That's because the shape of the black hole's event horizon in the EHT image could prove Albert Einstein's theory of how gravity works, or cast new doubt upon it.
In a nutshell (although one of seemingly immense density), Einstein said that gravity can actually warp the fabric of space-time, which is most easily thought of as the background that the Earth, the sun and everything else is moving through. So when a large star collapses on itself and turns into a very dense object with intense gravitational pull it has some serious warping power.
This crazy-dense super sucker is called the "singularity" at the center of the black hole. The singularity is so powerful that it warps space-time and bends light near the event horizon. So the singularity causing all this chaos is actually hiding somewhere behind the shadow of the black hole created by its own, spacetime-warping, light-consuming massiveness.
It all sounds a little insane, but there's lots of reason to believe Einstein has it right: most recently, the first observations of gravitational waves predicted by his theories helped to bolster those theories. But Einstein's theory of gravity, which seems to hold up when we look at big objects like stars and galaxies, is not compatible with quantum mechanics, the study of the bizarre, infinitesimal particles that make up atoms at the heart of everything.
According to Einstein's math, a singularity also has to be a really bizarre place. Being able to study images of the black hole it creates could lead to a better understanding of what's going on there, and maybe even new theories that bridge the gap between Einstein and the quantum world.
As astrophysicist Karan Jani put it in a wonderful tweet-lecture:
"The singularity of a black hole is a point of infinite density. All the laws of physics as we know break down here. But can such singularity exist in the real Universe? Or is it simply that our knowledge has not advanced enough to understand it?"
There are also other weird things going on at black holes, like the counterintuitive and powerful jets of near-light-speed particles that seem to be blasting across the universe. And what's on the other side of a black hole, anyway? Is it a white hole? A wormhole? A portal to another universe? These ideas might sound ludicrous, but at the moment they're all technically on the table, at least until we get a much better idea of what's going on beyond the event horizon.
And starting Wednesday, we just might enter that new era of understanding.
Originally published on April 8.