Black Hole Close-Up

More than a century ago, physicists made the first calculations hinting at the existence of one of our universe’s most bizarre oddities. The math suggested that space contains black holes—objects so massive and dense that nothing can escape after falling in.

Black holes remained mainly theoretical curiosities until the 1960s, when astronomers started to detect activity in space that could be best explained by the presence of these giant objects. Since then, researchers have continued to learn about black holes indirectly, by studying their effects on nearby stars and other matter. Scientists think smaller black holes form in the explosions of dying stars. The origins of the largest ones are still unknown. But they all share one unusual feature: The pull of their gravity—a force that attracts objects toward one another—is so strong, even light can’t escape.

More than a century ago, physicists made calculations that hinted at something strange. The math suggested that space contains black holes. They are among the oddest things in the universe. These objects are extremely massive and dense. Nothing that falls in can escape.

Black holes remained mainly just an interesting idea until the 1960s. Then astronomers started to detect unusual activity in space. The presence of these giant objects was the best explanation. Since then, researchers have continued to learn about black holes indirectly. They’ve studied their effects on nearby stars and other matter. Scientists think smaller black holes form when dying stars explode. How the largest ones form is still unknown. But they all share one unusual feature. It’s the pull of their gravity—a force that attracts objects toward one another. A black hole has gravity so strong, even light can’t escape.

Viewing a faraway object that traps light is no easy task. So even though astronomers have gathered plenty of evidence to confirm that black holes exist, until recently, they had never actually seen one. That changed in 2019, when a global collaboration of hundreds of scientists announced an amazing feat: They had captured the first image of a black hole. That remarkable photo and studies that followed are giving scientists new insights into black holes. Long shrouded in mystery, these objects are now revealing their secrets—and providing researchers with new data on some of the most extreme physics in the cosmos.

It’s not easy to view faraway objects that trap light. Astronomers have gathered plenty of evidence that black holes exist. But until recently, they had never actually seen one. That changed in 2019, when a global collaboration of hundreds of scientists announced an amazing feat: They had captured the first image of a black hole. Scientists are gaining new insights from that groundbreaking photo and studies that followed. Black holes have long been a mystery. But these objects are now revealing their secrets. They’re also giving researchers new data on some of the most extreme physics in the universe.

Unlike stars, black holes don’t give off light. They also don’t reflect light, like planets or moons do. That means there’s no way for light to travel from a black hole to a telescope, making the object basically invisible.

To capture the first image of a black hole, in 2017 researchers simultaneously aimed eight telescopes in different locations around the world toward a galaxy called M87. Scientists had long suspected that a giant black hole sits at the center of this collection of gas, dust, and stars, 55 million light-years from Earth. A lightyear is the distance light travels in a year—about 9 trillion kilometers (6 trillion miles)!

Working together, the eight telescopes formed a giant observatory nearly the size of our entire planet—a collaboration called the Event Horizon Telescope (EHT). It’s named for a black hole’s event horizon, which is essentially the point of no return. Once light (or anything else) crosses that boundary, it’s not coming back. 

Black holes don’t give off light, as stars do. They also don’t reflect light, like planets or moons do. That means light can’t travel from a black hole to a telescope. This makes the object invisible.

To capture the first image of a black hole, researchers used eight telescopes in different locations around the world. In 2017, they aimed all eight at once toward a galaxy called M87. This collection of gas, dust, and stars is 55 million light-years from Earth. A light-year is the distance light travels in a year. It’s about 9 trillion kilometers (6 trillion miles)! Scientists had long suspected that a giant black hole sits at the center of M87.

The eight telescopes worked together to form a giant observatory. It’s almost the size of our entire planet. The project is called the Event Horizon Telescope (EHT), named for a black hole’s event horizon. That’s the point of no return. When light (or anything else) crosses that boundary, it’s not coming back.

The EHT’s gargantuan scale created the precision needed to gather light swirling right outside the event horizon of M87’s black hole—the closest thing physically possible to a direct photo. If the idea of light “swirling” sounds odd, that’s just another quirk of black holes: Their gravitational pull is so strong, light passing nearby can’t travel in straight lines. Instead, its path bends and arcs. Light that gets too close to a black hole can briefly get stuck going in circles around it before falling in (see Dark Giant).

The EHT’s gargantuan size made it very precise. It could gather light swirling right outside the event horizon of M87’s black hole. That’s the closest thing physically possible to a direct photo. The idea of light “swirling” might sound odd. But that’s just another strange thing about black holes. Because their gravitational pull is so strong, nearby light can’t travel in straight lines. Instead, its path bends and arcs. If light gets too close to a black hole, it can briefly get stuck going in circles around it. Then the light falls in (see Dark Giant).

Scientists spent nearly two years analyzing the observations from all eight telescopes and combining them into a single image. That unprecedented first portrait shows an irregular ring of light. At its center lies a dark shadow: the black hole’s event horizon (see Doughnut Hole?).

For nearly two years, scientists analyzed the observations from all eight telescopes. They combined the data into a single image. That first-ever portrait shows an irregular ring of light. At its center lies a dark shadow. It’s the black hole’s event horizon (see Doughnut Hole?).

“There’s just something beautiful about that shadow,” says astrophysicist Daryl Haggard of McGill University in Canada. “Once you see it, you don’t forget it. People had predicted it might be possible to delve right down to the event horizon, but it was incredible to see it actually happen,” she says.

The shadow in the image relates to the black hole’s mass, the amount of matter it contains. More massive black holes have bigger shadows. By measuring the silhouette, astrophysicists were able to make the most direct estimate yet of this black hole’s mass: about 6.5 billion times that of our sun.

“There’s just something beautiful about that shadow,” says Daryl Haggard. She’s an astrophysicist at McGill University in Canada. “Once you see it, you don’t forget it. People had predicted it might be possible to delve right down to the event horizon, but it was incredible to see it actually happen,” she says.

The shadow in the image relates to the black hole’s mass. That’s the amount of matter it contains. More massive black holes have bigger shadows. Astrophysicists measured the shadow to make the most direct estimate yet of this black hole’s mass. It’s about 6.5 billion times that of our sun.

In March 2021, the groundbreaking image got a dramatic update to include the effects of the black hole’s magnetic field—a phenomenon that exerts a force on moving charged particles. When light passes through such a field, it can become polarized, so all its waves have the same orientation in space. Reprocessing the data from the 2017 observations revealed this polarized light. That allowed scientists to see the signature of a twisting magnetic field just outside M87’s black hole.

In March 2021, the groundbreaking image got a dramatic update. Now it includes the effects of the black hole’s magnetic field, which exerts a force on moving charged particles. When light passes through a magnetic field, it can become polarized. All its waves vibrate in the same direction. Researchers reprocessed the data from the 2017 observations to reveal this polarized light. Then scientists could see the signature of a twisting magnetic field. It was just outside M87’s black hole.

The updated image may hold clues to another of the black hole’s incredible features. It appears to shoot material from just outside its boundary in forceful streams nearly 10,000 light-years long that stretch across the galaxy. “We see this huge funnel of stuff absolutely flying out from them galactic center,” says Haggard.  Astronomers are perplexed as to how any single object—even one as intense as a black hole—can possibly create that cosmic spectacle.

The updated image may hold clues to another incredible feature of the black hole. It appears to shoot material from just outside its boundary. It sends out forceful streams nearly 10,000 light-years long. They stretch across the galaxy. “We see this huge funnel of stuff absolutely flying out from the galactic center,” says Haggard. Astronomers are trying to figure out a mystery. How can any single object, even one as intense as a black hole, create that giant spectacle?

“These jets are so powerful, the matter they contain is moving at almost the speed of light,” says Monika Moéscibrodzka, an astrophysicist at Radboud University in the Netherlands. Light travels at 299,792 km (186,282 mi) per second, thought to be the maximum speed limit for anything in our universe. The driving force fueling the jets remains a mystery, but scientists suspect magnetic activity around the black hole may play an important role.

To learn more about the jets, researchers aimed 19 telescopes at them at the same time the EHT was observing the black hole itself. That resulted in a new series of images, released in April, that could help scientists figure out this baffling phenomenon.

“These jets are so powerful, the matter they contain is moving at almost the speed of light,” says Monika Mocibrodzka. She’s an astrophysicist at Radboud University in the Netherlands. Light travels at 299,792 km (186,282 mi) per second. Scientists think that’s the maximum speed limit for anything in our universe. The driving force behind the jets is a mystery. But scientists suspect magnetic activity around the black hole may play an important role.

To learn more about the jets, researchers aimed 19 telescopes at them. At the same time, the EHT was observing the black hole itself. The result was a new series of images, released in April. These images could help scientists figure out the baffling puzzle.

Astrophysicists hope their black hole photos will help them learn how these strange objects form, behave, and expand. The images will also allow scientists to check how their current understanding of gravity, magnetic fields, and matter holds up against one of the most extreme situations in our universe. “The conditions near black holes are beyond anything we can create in a lab,” says Haggard. “Observing them is a great way to test our theories.”

Astrophysicists want to learn how black holes form, behave, and expand. They hope their black hole photos will help. The images will also allow scientists to check their current understanding of gravity, magnetic fields, and matter. How will their ideas hold up against one of the most extreme situations in our universe? “The conditions near black holes are beyond anything we can create in a lab,” says Haggard. “Observing them is a great way to test our theories.”