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The lives of black holes, from birth to death

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The lives of black holes, from birth to death

The lives of black holes, from birth to death

AhmadJunaidTechnologyMay 21, 2026358 Views

Of all the strange and spectacular things in outer space, nothing is stranger or more spectacular than black holes.

These cosmic oddballs can’t even be described without contradiction. Unlike a typical hole, for instance, a black hole is not empty. Its core packs so much matter that its density is almost impossible to imagine. The smallest known black holes squeeze more than three times the mass of the sun into a volume about the diameter of a small city. One of the largest that scientists have found contains more than tens of billions of times the mass of the sun and stretches across a space bigger than the solar system.

Because it holds so much mass in such a small space, nothing that gets too close to a black hole can escape its gravity — not even light. Yet to find black holes, scientists must look for the brightest beacons of light in space. (This light is given off as the black hole feeds on nearby gas.)

Black holes have been known to devour stars, planets and even other black holes. The superstrong gravity of supermassive black holes allows them to hold giant galaxies together.

Scientists have been grappling with the strangeness of black holes for centuries. John Michell appears to be the first person to have predicted their existence. Back in 1783, he proposed there might be “dark stars” with gravity too strong for their own light to escape.

More than a century later, in 1915, Albert Einstein proposed his theory of general relativity to describe how gravity works. That theory predicted matter could collapse into a single point of infinite density — a black hole. Its mass would be so extreme that it would warp the space around it. The result: Anything passing nearby would be pulled into it.

Decades after Einstein introduced this idea, X-ray telescopes confirmed such weird objects exist. Researchers observed blasts of high energy as black holes fed. And in 2019, the Event Horizon Telescope captured the first direct image of a feeding black hole.

In 2019, astronomers captured the first ever image of a black hole. They used the Event Horizon Telescope, which is not one device but a worldwide network of connected radio telescopes.Event Horizon Telescope Collaboration

Yet some of the most basic questions about these cosmic monsters remain unanswered. Astrophysicists don’t know, for instance, why galaxies host giant black holes in their hearts. And then there’s those supermassive monsters. How did they get so gargantuan? In fact, “where do they come from?” asks Marta Volonteri. This astrophysicist at the Paris Institute of Astrophysics in France has developed models of how black holes might form. And there are no clear answers for how the biggest ones do, she says. After 20 years of searching, she says, “I still don’t know.”

Scientists also are working to explain how black holes change over their lifetimes and how they might eventually die. Powerful telescopes and models of the universe have offered up some good ideas. Yet the more scientists learn, the more they realize how little they know.

This video illustrates the history of our understanding of black holes, from the conditions under which black holes form to the sizes they can take, where they’re found and how they behave.National Geographic/YouTube

A black hole is born

Black holes come in a range of sizes. Small ones contain up to 100 times the mass of the sun. Supermassive ones can have millions to tens of billions as much heft.

This size range poses a big problem in explaining how black holes form.

Traditionally, we have understood black holes to be “stellar corpses,” says Priya Natarajan. She’s an astrophysicist at Yale University in New Haven, Conn.

That seems to be true for the smallest ones, which scientists describe as “massive.” They form from stars with about 20 to 30 times the mass of our sun. As they’re dying, these big stars explode as supernovas, leaving behind black holes.

Scientists know basically how this works.

During active phases of their lives, stars fuse lighter elements into heavier ones, producing heat and light. Eventually, though, a star runs out of fuel. If it was the size of the sun, it will swell up as it dies. Later, it will collapse into a small, glowing core of oxygen and carbon.

But when bigger stars run out of fuel, look out! They’ll end up with an unstable iron core that keeps pulling in mass.

Eventually, that core will collapse under its own weight. This may trigger an explosive supernova. What’s left behind just keeps collapsing into an increasingly dense ball. Stars that started with between eight and 20 times the mass of the sun will collapse to make a neutron star. Its pressure crushes its particles together.

Bigger stars, though, become a black hole. (They may or may not go through a supernova phase first.) These are called “stellar-mass” or “massive” black holes. Astronomers predict that scattered around our galaxy are hundreds of millions of massive black holes.

They’re very different from the supermassive types often found at the centers of galaxies.

Sagittarius A* sits at the center of our Milky Way. This heavyweight carries as much mass as 4 million suns. The black hole at the center of Andromeda, our nearest galactic neighbor, has the mass of more than 100 million suns. The largest black hole known — TON 618 — contains 66 billion times our sun’s mass.

But even the largest stars don’t have nearly that much mass. So how truly monster black holes arise poses an interesting puzzle, says Natarajan: How could they get so enormous?

Black holes grow at least two ways, she notes. “They either gobble gas and material from around them, or they collide with other black holes.”

When black holes smash together, the collision produces gravitational waves that ripple through the fabric of the universe. Scientists have begun detecting these waves using sensitive, underground observatories. MARK GARLICK/SCIENCE PHOTO LIBRARY/ALAMY STOCK PHOTO

Galaxies are vast collections of stars. When they collide, the supermassive black holes at their centers may essentially fuse.

Here, “the black holes dance around each other and merge,” says Volker Springel. Now, he notes, “you’ve got a bigger one.” Springel is an astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany. That dancing and merging happens frequently, he says. “So we expect, in the future, [we’ll get] slightly bigger black holes even than the biggest ones we have today.”

But not even collisions can explain how today’s supermassive black holes got so big, says Natarajan.

Observations of some of these behemoths suggest they formed when the universe was young. To get so big, they’d have had to grow stepwise from collision after collision after collision — or spend eons successively eating more and more stars and other mass entering their neighborhoods.

Yet, Natarajan points out, there’s simply not been enough time since the Big Bang for them to have grown that big if they were “starting from a piddly little stellar corpse.”

The supermassive mystery

Surrounding every black hole is an event horizon. That’s a point of no return. Once any information — including light — passes that horizon, it can never be retrieved. That means scientists can’t analyze the contents of black holes to figure out how or when they formed.

Simply put, says Natarajan: “They don’t have any memory.”

Scientists have found other ways to study them, though. In the 2000s, Natarajan and other astrophysicists proposed that supermassive black holes might grow from giant black hole “seeds.” These might have formed from something other than a dying star.

Gravity might have collapsed a massive cloud of gas to form a black hole, even before it became a star. These black hole seeds — each with a mass of about 1 million suns — might have merged to quickly form larger ones. Seeds that formed right after the Big Bang, Natarajan says, might have had time to spin up into the supermassive black holes we see today.

This artist’s illustration portrays a close-up look at a black hole drifting through our galaxy, the Milky Way. Such objects are the crushed-up remnants of massive stars that exploded as supernovas. Scientists suspect our galaxy may host 100 million stellar-mass black holes, as well as a supermassive one at its core.FECYT, IAC via NASA Goddard

“There are certain conditions under which you can have gas that will … directly collapse into a black hole,” she says. “It doesn’t have to go through a star stage.” The gas has to be made of pure hydrogen and helium, for example, with more gas constantly flooding in.

Volonteri of the Paris Institute has also studied the formation of such seeds and their potential to have produced what are now supermassive black holes.

In 2023, scientists spotted the bright center of a galaxy more than 10 billion light-years away. It was fueled by a black hole with the mass of about 40 million suns. It was so big, relative to the size of its galaxy, that scientists described it as “over-massive.” Even more impressive: This black hole likely formed when the universe was in its infancy (just a few hundred million years old).

That discovery, called UHZ1, fits with Natarajan’s models. It likely started as some giant black hole seed that formed after the collapse of an enormous cloud of gas.

Black hole evolution

To study how black holes evolve, scientists must get creative. By focusing on stuff that surrounds a black hole, they can make educated guesses on how the beast is behaving.

Stellar-mass black holes generally remain quiet and unchanging. Unless, that is, something begins to orbit too closely — such as gas, dust, a planet or a star. Then, the black hole’s strong gravity may rip the intruder apart and gobble it up. As remains of the intruder fall into the black hole, the disintegrating stuff burns up, producing bright bursts of radiation.

What’s happening in supermassive black holes is more puzzling. Most galaxies have a supermassive black hole at their center. No one knows which came first, the galaxy or the black hole. In fact, Natarajan suspects, they likely formed at the same time.

Watching how a galaxy changes, she says, can hint at how its black hole is behaving.

To get bigger, black holes feed on anything that gets near them. They can even be cannibals. Listen as several astrophysicists describe such colossally energetic feeding events.Science Channel/YouTube

What’s more, “black holes are believed to be a major factor in galaxy evolution,” says Springel at the Max Planck Institute. For instance, supermassive ones can control the size of their host galaxy. If they didn’t, he says, this collection of stars — the galaxy — would “continue to get bigger and bigger.” And here’s why.

Dense clouds of hot gas move throughout a galaxy. As these clouds cool, they can condense to form stars. The Milky Way produces an estimated three or four new stars each year. So-called starburst galaxies can spawn hundreds per year.

But galaxies can’t grow infinitely large. “There’s a pretty hard maximum,” Springel says. It’s about 1 trillion times the mass of our sun. (A rare few are estimated to be 10 trillion solar masses.)

The reason for this limit may be that a black hole and a galaxy tend to grow in lockstep. The galaxy makes more stars. Then the black hole ingests more gas, stars or other nearby stuff and grows. As the black hole eats, it produces powerful jets of energy.

Scientists used to believe that all the jets’ energy would escape and “not do much damage to the galaxy,” says Springel. But computer models by his team and others now tell a different story.

Black holes can act like a thermostat for a galaxy, keeping the heat on, Springel finds. The jet’s bonus energy can superheat clouds of gas. When that happens, big galaxies can’t cool enough to form stars. “There’s a trickle of star formation sometimes left,” he says.

It’s different in smaller galaxies. Black holes that don’t produce so much energy can still give birth to new stars.

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Black hole mortality

Black holes lead dynamic lives. Within the last year alone, scientists have made several surprising discoveries. One team found evidence of a type of black hole collision so massive that scientists had thought it impossible. Other astronomers spotted a runaway black hole that had likely been booted from its galaxy — dragging a trail of newborn stars behind it.

The stars that produce massive black holes only live for a few million years. But their surviving black holes, models suggest, stick around for billions of years or more. With such lengthy lives, black holes have a long, long time to interact with each other and everything else.

Scientists predict that within the next 10 billion years or so, the Milky Way might merge with the Andromeda galaxy. (Estimates that this will happen range from less than 50 percent to near certainty.) If these galaxies merge, their black holes will, too, producing an even bigger one. Galaxies and their black holes elsewhere in the cosmos will continue colliding, too, says Springel — but likely not forever.

The universe is expanding. It’s unclear if that expansion will continue without end. But if it does, galaxies will get ever farther apart. If there’s a Milky Way-Andromeda merger, says Springel, this super-galaxy will become a kind of bright but dimming island in a vast sea of dark, empty space.

Eventually, “all the galaxies will stop merging with each other,” he says. “They’ll become isolated.”

For a while, they’ll keep making new stars. As those suns eventually die in supernovas, new black holes will form. In time, though, galaxies will run out of star-making stuff. All their stars will eventually run out of fuel — and go dark.

Some theories suggest that all the matter from dead stars and planets may also break apart. In the end, black holes may be the last survivors in our universe.

And even they may die.

Evaporating out of existence?

In 1974, astrophysicist Stephen Hawking predicted that black holes could “evaporate.” That is, they could fall apart by gradually releasing radiation.

This evaporation would develop through a process described by a field of physics called quantum theory. It predicts that the emptiness of space undergoes fluctuations as tiny particles pop in and out of existence. Because of how these particles behave near the outer edge of a black hole — its event horizon — they can reduce its mass.

Although no one has directly observed Hawking radiation, the idea mostly fits with scientists’ current ideas about the physics of black holes.

“The smaller the black hole is, the quicker they will do this,” says Springel. At the end of the universe, the smallest black holes will be the first to shrink.

What happens next remains a mystery.

Supermassive black holes may evaporate one day, too — or not. Recent research suggests that some strange physics may halt their death throes. These theories suggest a black hole cannot lose all the “information” it had acquired. So their evaporation may stop once such beasts have lost half their mass.

Some physicists have proposed an even wilder idea: that a star may collapse into something called a black shell. It sort of mimics a black hole. Here, all the collapsing mass forms a dense outer shell. Inside would be what scientists call a “true vacuum” — a volume with the absolute lowest energy possible.

But that’s just an idea.

With every question scientists answer about how black holes form, live or die, they uncover new, even stranger questions. After all, they’re studying the most extreme things in all of nature.

Frustrating as it is, black holes “represent the end of knowledge,” says Natarajan. Simply put, she says, they’re “the edge of what we can know.”

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