Dan Marrone, a University of Arizona astronomy professor, led the Event Horizon Telescope team’s effort to capture the first image of a black hole.
Dan Marrone was alone in a Minnesota cabin one afternoon five summers ago. While his family was lake swimming, he logged on to his computer and waited for the big meeting to start. Members of his scientific team were going to reveal a picture they’d worked for years to get: the first-ever portrait of a black hole, very up close and extremely personal.
Marrone, a professor at the University of Arizona, sat back with a vacation beer and prepared for the show-and-tell of the black hole at the center of a galaxy named M87. He watched his screen and waited.
This article appears in Issue 23 of Alta Journal.
Supermassive black holes like M87’s, which is more than 6.5 billion times as massive as the sun, are the universe’s most extreme objects, with matter crushed together into such a small space that even light can’t escape the great gravity. They’re at the centers of most galaxies, which makes them fairly common (astronomers don’t know precisely how many galaxies exist in the universe, but data from the New Horizons spacecraft indicates there are hundreds of billions out there), yet no one had yet produced a picture of one.
Scientists like Marrone cannot peer inside the infinitely dense depths of black holes, which remain experientially unknowable, but they can look at the light immediately outside those disks of darkness, in the area where a black hole becomes black—a terrifying place called the event horizon.
When the shot of M87’s core finally appeared as pixels on Marrone’s screen, he and his fellow team members celebrated. After their jubilation subsided, Marrone was, as much as anything, relieved. The black hole looked like a black hole should. Which wasn’t very impressive: it resembled a doughnut, glazed shinier on one side than the other, that had been set atop a black party napkin and photographed fuzzily.
But Marrone found it beautifully concrete. The middle of the doughnut was the literal shadow of a literal black hole; the glazed torus showed light bending and whipping around in the hole’s intense gravity. For so long, black holes had been math and inference. Now this one, at least, was a thing.
And it was a thing made possible by a project Marrone had worked on since it started in 2009, called the Event Horizon Telescope. He and colleagues had cleverly strung eight telescopes together—from California to Chile, from Greenland to the South Pole, and from France to Arizona—linking them in such a way that they acted like a single observatory the size of the globe. And there, in his cabin, Marrone saw the EHT’s first fruits, which would not be revealed to the public till the next year, when the team would be confident that its results would hold up to scientific scrutiny. “I couldn’t tell anyone, but I had a nice, relaxing rest of that week,” he says.
He finished his beer, alone with his team’s secret: he and a select group of other scientists had seen something previously unseeable.
More than half a year later, in April 2019, the rest of us did too. The EHT made big headlines then, and it’s continued working ever since, checking out black holes in multiple observation campaigns. The project has added several telescopes to its arsenal, including, in 2019, an instrument on Kitt Peak, a mountain in Arizona. Data from the EHT will help scientists determine whether Einstein’s theory of general relativity is fully accurate—whether the universe at its extreme edges behaves as he predicted.
But black holes aren’t just esoteric testing grounds: they’ve also played a major role in determining how the universe looks today and how it got that way. Their mass, energy, and eating habits have shaped the cosmos for eons. They help reveal, in other words, evolution on the largest scale. “There’s enough there to make us go to the ends of the earth to try and study them,” says Marrone. He means it.
MORE THAN PRETTY PICTURES
The EHT’s snapshots aren’t the be-all and end-all for the astronomers. “Those doughnut pictures are just pretty pictures, where ‘pretty’ may be defined loosely,” admits Marrone. “We didn’t learn that much.” Knowledge about a black hole comes from deeper data, which the scientists find by looking, for instance, at the orientation of the light waves leaving it and trying to understand how material flows into the abyss, how jets of hot stuff flow out, and how its supercharged magnetic field works. The researchers discovered, for example, that a black hole’s magnetic field can be strong enough to stop plasma—a substance that makes up around 99 percent of the universe and is so hot that atoms are stripped of their electrons—from falling into the no-return zone. The plasma is also more stable, and less variable, than they expected. “To this day, we don’t know why,” says Chi-Kwan Chan, an associate research professor at the University of Arizona’s Steward Observatory and an EHT team member.
Chan got his start in the field years ago, programming a new supercomputer to do simulations of black holes, and went on to devise the simulations showing EHT scientists what they could expect—which informed the design of their telescope instruments. Today, he develops the software that sucks in and synthesizes data from each observation run by the project’s 11 telescopes. Recently, his code and the team’s analysis produced a second black-hole glamour shot: of the one in our Milky Way. Surprise: it’s another doughnut, with glazily bright areas spread around its core. But that doughnut is central to our existence.
Meanwhile, the uncertainties the team encounters—the holes in our knowledge, if you will—are actually good, in Chan’s opinion. “When we see something unexpected, we’re actually happy,” he says. “Because that means we can learn something new.”
11 TELESCOPES AS ONE
The EHT team began preparing well in advance for its March 2022 observation campaign. Previously, Marrone and graduate student Arash Roshanineshat had worked hard to bring the Kitt Peak 12-Meter Telescope online. It needed a new receiver—kind of like a camera for a radio telescope—to be able to detect black holes, and engineers had to build one. Then Marrone’s team had to install it and test it, along with a whole lot of electronics and an atomic clock, to capture and record the signal and ultra-precisely align the 12-meter’s observations with those of the 10 other telescopes. “Every time you put one of these sites together, they’re just different,” says Marrone.
And for each one, the team has to sweat the details, like whether electrical currents beneath the 12-meter’s building might mess with the atomic clock’s timing. “We have to worry about how the cables flow, and will the wind blowing on them change the temperature and change their electrical length and make the signal wiggle in time?” says Marrone, sounding a bit frantic even now.
Those hands-on aspects are what Roshanineshat, an electrical engineer, enjoys the most, and fellow team member Amy Lowitz, an EHT scientist at the University of Arizona, agrees. She trains researchers at the South Pole to do EHT observations during the Antarctica winter—the place and time on the planet perhaps most like a black hole. “It’s not all sitting at a desk, staring at numbers,” she says. “There’s this whole other world of getting your hands dirty and crawling around on the floor, fixing a telescope, and moving cables around and soldering tiny things and threatening large telescopes with large wrenches to get them to work.”
It’s like fixing your sink, in other words, on a different scale.
A few weeks ahead of the March 2022 observations, Roshanineshat returned to the Arizona high country to inspect and rewire the telescopes and communication devices as needed. He remained there during the weeklong campaign: he was in charge of running the instrument this season.
The Kitt Peak 12-Meter, which detects radio waves, is Roshanineshat’s favorite telescope. He likes the shape of the dome that covers the antenna when it’s not in use but opens like a gargantuan clamshell when he commands it to. “Maybe because I spend a lot of time up there, that created a connection,” he says, “between the telescope and myself.”
During the campaign, commands that Roshanineshat had prepared earlier guided the telescope’s gaze from one black hole to another to another, and, simultaneously, the other, networked telescopes peered at the same strange objects, a planet-size cryptid with many eyes. He checked whether the black holes’ signals were coming through and streaming into the bank of storage disks. He couldn’t see what the gathered information might reveal: it comes in at too fast a rate to do anything but commit it to computer memory, so the objects remained as invisible to him as to everyone else.
As he watched the telescope go from black hole to black hole and move toward their individual darknesses, he felt proud. The cosmic objects had released the energy the telescope was picking up millions of years ago. He was observing them as they had been, long before humans were a glimmer in earthly evolution’s eye.
After each campaign, the EHT team mails hundreds of hard disks from its sites to the Max Planck Institute for Radio Astronomy in Bonn, Germany, and to the Massachusetts Institute of Technology’s Haystack Observatory for analysis. There, they’re “correlated,” meaning that specialized computers spin their signals together, digitally pretending that the output from 11 sites all came from one very large instrument. The results are further scrutinized to make sure nothing went awry. “Then, finally, we have something that is sort of a draft data set that we can start trying to make images with,” says Marrone.
Already, the data is proving to hold more than doughnut images. Marrone, for instance, has watched a black hole wiggling around. “It’s kind of like a twinkling of a star in the sky,” he says. “We know it’s doing something really fast.”
In the months ahead, the team might learn more about how that “something” works, because it’ll be adding a higher frequency of radio waves to its observations—kind of like taking a picture with a red lens and then a blue lens and putting them together—which means it’ll get sharper images, nittier-grittier data.
And the EHT’s ability to grasp the mostly invisible is also being strengthened by another instrument: the James Webb Space Telescope, NASA’s flagship observatory that launched in December 2021 and came online last year. The JWST can’t see black holes in the way the EHT can. Its gaze can pierce the dust near galaxies’ cores to see gas nearby and measure how fast it’s flowing outward, and it can detect the presence of individual chemicals. These capabilities can help researchers understand how black holes eat and get bigger.
Later this year, the JWST will join the slate of EHT instruments as they shed more light on our own galaxy’s black hole, how it and others molded themselves, and how they shaped the universe. As Marrone promises, the EHT will go not just to the ends of the earth but also beyond.•