Humankind has finally come face to face with a black hole. Sort of.
At 9 a.m. Eastern Daylight Time this morning, scientists unveiled the first set of results from the Event Horizon Telescope, a network of eight radio observatories that used its combined powers to peer deep into the center of Messier 87 (M87), a galaxy 55 million light-years away.
What greeted it was the spectral silhouette of a supermassive black hole, 6.5 billion times as massive as our own Sun, shrouded in a lopsided halo of light.
“The first time I saw the image, I was completely blown away,” says Event Horizon team member Jordy Davelaar, an astrophysicist at the Flatiron Institute’s Center for Computational Astrophysics and Radboud University Nijmegen. “My heart skipped a beat. I had goosebumps all over.”
The first four images of M87’s black hole are available in a series of papers published today in the journal Astrophysical Journal Letters.
Black holes are, by definition, so dense and massive that no light can escape their ravenous gravity—which means a silhouette is about as direct as it’s going to get. All that backlighting comes courtesy of light bending around the black hole, and the bright, hot swarm of gas that surrounds it.
Compared to the countless illustrations and simulations that have been produced over the years, the new images might seem underwhelming. With a bit of residual noise and smear, their contents look a bit like an blurry circle of fire, snapped with an old-school camera.
But given the elusive nature of these enigmatic objects, what’s been captured is “simply mind-blowing...a thing of pure beauty,” says Raffaella Margutti, an astrophysicist at Northwestern University who was not involved with the Event Horizon team.
“We’ve been studying black holes so long that sometimes it’s easy to forget that none of us has actually seen one,” National Science Foundation Director France Córdova said at a press conference, right before the first image was revealed.
That statement is no longer true.
The new images are precise enough to demarcate a stunning outline of the black hole’s event horizon, or the boundary past which even something traveling at the speed of light could not escape the object’s gravitational pull. Unlike their predecessors, these visuals are, at long last, more than mere renderings of the imagination—and they appear to offer gratifying confirmation of some of Einstein’s original predictions about general relativity.
“Science fiction has become science fact,” team member Avery Broderick, a theoretical physicist at the Perimeter Institute and the University of Waterloo, said in this morning’s press conference.
It’s been over a century since Albert Einstein first proposed his theory of general relativity, wherein massive objects, like our own Earth, can subtly but detectably warp space and time, like a bothersome pea under a mattress. Gravity itself arises from this spacetime curvature.
But at the extremes of these equations lies a prediction that Einstein himself once thought preposterous: If an object is dense enough, it could transform spacetime into an impossibly voracious pit of cosmic quicksand from which nothing, not even light, could escape. In other words, a black hole.
Studies on black holes began in earnest many decades ago. But before now, no direct observations had been possible. To pinpoint their existence, scientists relied on indirect measures, like tracking the paths of stars or gases, which behave aberrantly when orbiting black holes. They then inferred what lies within—a challenge akin to guessing the flavor of a cake by examining the tin it was baked in.
“There were limitations about what these data could tell us about the black hole itself,” says Emily Rice, an astrophysicist at the College of Staten Island who was not involved with the Event Horizon Telescope team. “It was just, ‘It should be a black hole.’”
But that didn’t stop scientists from modeling what they thought black holes probably looked like. And when put head to head with previous simulations, today’s images ring astoundingly true to form. “This is pretty much what we hoped to see,” says Emily Levesque, an astronomer at the University of Washington who was not involved with the Event Horizon team.
The Event Horizon Telescope network first captured data on M87’s black hole in April of 2017. A team of scientists then spent the next two years compiling and analyzing the results. With its synchronized, global array of observatories, the Event Horizon Telescope effectively forms one mega-telescope as big as Earth itself—one that’s discerning enough to resolve objects millions of light-years away.
With this kind of magnification, you could “[read] the date on a quarter in Los Angeles [while] standing in Washington, DC,” Event Horizon Team member Shep Doeleman, an astronomer at Harvard University, said in this morning’s press conference. Basically, it’s a giant, planet-sized eyeball, with vision about 3 million times sharper than 20/20.
Over the course of about a week of observations, each telescope in the network collected about a petabyte, or a million gigabytes, of information. With its powerful combination of linked telescopes, the Event Horizon team was able to generate images of a shadow of what lies at the dark, dark heart of M87.
“We are delighted to report that we have seen what we thought was unseeable,” Doeleman said during the press conference.
The cosmic sink hole’s eerie glow is actually of its own making. Black holes aren’t dormant beasts: They’re constantly devouring gas and cosmic matter. As these celestial objects circle the drain, they heat up, shrouding the event horizon in a cloud of detectable energy and emitting bursts of light. Just outside the event horizon, gravity is strong enough to bend the path of light into something that resembles a bright, glowing donut. The size and shape of the shadow are in keeping with what we know of general relativity—and constitute “yet another feather in Einstein’s cap,” Rice says.
“For general relativity, this is a major victory,” Davelaar says. “A black hole is a fundamental object predicted by [the theory]...for general relativity, this is just incredible.”
The ring of light that encircles the black hole isn’t perfectly symmetrical: In the image, one half is brighter than the other. “This is probably caused by the rotation of the material and the black hole,” Davelaar says. “It’s like hearing an ambulance. If it travels towards you, you hear another pitch. The same happens with light.”
What the Event Horizon Telescope detected here on Earth were the radio waves emitted from M87’s black hole. But it’s a marvel that these energetic waves of light reached us at all. They’ve had to elude the gaping maw of the event horizon, cut through millions of light-years of intergalactic space, and evade absorption by the water vapor in our planet’s atmosphere. (That’s why the network’s observatories are all stationed at arid, high-altitude locales).
Radio waves with a wavelength of 1.3 millimeters have a frequency that’s “perfect” to make this harrowing odyssey, Doeleman said in the press conference. And these waves are exactly what the Event Horizon Telescope was set up to detect. In effect, that pesky gravitational pea has been felt through not just one mattress—but millions.
Of course, this is just the beginning. The telescopes that collected the data on M87’s black hole are only a subset of the Event Horizon network—and this far-flung galaxy’s cosmic innards weren’t their only target. In fact, until this morning, it wasn’t clear which results the team would present: M87’s black hole was just one of two options on the menu.
During the same period of observation, the array was also hard at work monitoring another supermassive black hole much closer to home: Sagittarius A*, which lies at the center of our own Milky Way, 26,000 light-years from Earth.
And many questions remain. Supermassive black holes might actually hang out in the middle of nearly all large galaxies, but their origins are still somewhat mysterious. And there’s a bit of a chicken-and-egg issue: Black holes could spring up from newly-birthed galaxies…or they could play a role in the formation of galaxies themselves.
Additionally, while the wonky halo of M87’s event horizon is a marvel in and of itself, the true mystery lies in the belly of the beast—the center of that alluring abyss. The core of a black hole is likely a realm in which all known physical laws essentially break down, where matter is stripped down to its most basic forms.
At least, that’s what scientists think. Even the most intrepid astronauts aren’t keen on a black hole sojourn. For now, everything we know about what happens within the event horizon remains theoretical.
But in the meantime, it’s good to know it’s there.
“All of us, even people who professionally study black holes, still just turned into little kids when we saw that image,” Levesque says. “The excitement of it is wonderful in its own right. And the science we’ll get out of will be wild.”