Space is weird. Black holes? They break your brain.
You can’t describe them without stepping into contradiction. A typical hole is empty, right? Wrong. A black hole is dense. Insanely dense. The small ones cram more mass than the Sun into a space roughly the size of Manhattan. The big ones? They stretch larger than our solar system, weighing billions of Suns.
So why do we look for light to find the darkest things? Because when they eat gas, they scream. Brightly. 📣
We know they devour stars, planets, even other black holes. They hold galaxies together like cosmic glue. But the math gets tricky. And the history? Even stranger.
The Long Weirdness
John Michell got the idea first, way back in 1783. He called them “dark stars.” Stars so heavy their own light couldn’t escape. Simple concept. Hard reality.
Then came Einstein in 1915. General Relativity changed the game. It predicted matter could crush itself into a point of infinite density. Space itself warps around this point. If you get close? You fall in. No climbing back.
Decades passed. Nothing proved it. Until the X-rays hit.
Telescopes picked up high-energy blasts as these invisible giants fed. In 2019, we finally got the picture. The Event Horizon Telescope showed us the shadow of a feeding monster. Real proof.
But the puzzles remain.
Where do they come from?
“Where do they come from?”
— Marta Volonteri
Volonteri studies black hole formation models at the Paris Institute. After twenty years of trying to figure it out? She still doesn’t know how the biggest ones got so huge.
Born to Die?
Size matters here. Small black holes weigh up to 100 Suns. Supermassive ones weigh tens of billions.
The small ones are dead stars.
Priya Natarajan, an astrophysicist at Yale, calls them “stellar corpses.” When a massive star—about 20 to 30 Suns—runs out of fuel, it explodes. Supernova. 💥 The core collapses. Gravity wins. Boom. Black hole.
If the star is smaller—8 to 20 Suns—it might become a neutron star. Particles crushed together by pressure. But go bigger than that? Total collapse. Stellar-mass black holes. There are hundreds of millions hiding in our Milky Way, mostly quiet and lonely.
But the centers of galaxies? They host monsters.
Sagittarius A, our neighbor in the Milky Way, weighs 4 million Suns. The one in Andromeda is over 100 million. The champion, TON 618, is 66 billion* times the mass of the Sun.
Here is the problem: No star is that heavy. So how did TON 618 get there?
They eat. Gas, stars, other black holes.
When galaxies collide, their central black holes dance and merge. Volker Springel at Max Planck says they spiral around each other until they fuse. Bigger than before. This happens all the time. We should expect even bigger ones in the future.
But merging isn’t fast enough.
Some supermassive black holes existed when the universe was tiny. Just a few hundred million years after the Big Bang. They didn’t have time to grow by eating little stars one by one.
There simply wasn’t enough time.
The Supermassive Mystery
Black holes don’t have memories. Once light crosses the event horizon—the point of no return—it’s gone. We can’t see inside. We can’t check the receipt to see what it ate.
So we guess.
Natarajan suggests they might grow from “seeds.” Not dead stars. Huge clouds of pure hydrogen and helium gas that collapsed directly into black holes before becoming stars. No supernova. No messy transition. Just a massive, sudden plunge.
These seeds could be millions of Suns heavy from day one. Merge a few times. Eat a bit. Voila: Supermassive.
In 2023 we found evidence. UHZ1. A galaxy over 10 billion light-years ago hosted a black hole weighing 40 million Suns. It was huge compared to its tiny home. Over-massive.
It fits the seed theory. The universe’s infant black holes started big, not small.
Life With a Monster
Studying their evolution requires looking at the surroundings. The stuff getting torn apart tells the story.
Stellar-mass holes are quiet. Until a planet gets too close. Then gravity rips it apart. The debris burns up, flashing bright radiation. Drama. 🎭
Supermassive holes are different. They live in the centers of galaxies. Which came first? The chicken or the black hole?
Natarajan thinks they formed at the same time.
They might actually control each other. Black holes act like thermostats for their host galaxies.
Hot gas clouds in galaxies cool down and form stars. The Milky Way makes a few every year. Starburst galaxies? Hundreds.
But there’s a limit. Springel notes a hard cap of about 1 trillion Solar masses for a galaxy.
Why?
As a galaxy makes stars, the central black hole eats the leftover gas. As it eats, it spits out powerful jets of energy.
We used to think that energy escaped harmlessly. We were wrong.
Those jets heat the gas. They prevent it from cooling. No cooling means no new stars. The galaxy starves. The black hole stops the party. 🚫
It’s a feedback loop. A cosmic off-switch for growth. In smaller galaxies, where the black holes aren’t quite as powerful, this brake doesn’t work as hard. Stars keep being born.
The End of the Party
Black holes are dynamic. They don’t just sit there.
Recent finds show massive collisions we thought impossible. Runaway black holes kicked out of their homes, dragging newborn stars behind them like a comet tail.
Stars live short lives—millions of years. Black holes last billions.
Eventually, everything gets lonely.
In 10 billion years, our Milky Way might collide with Andromeda. If the math holds, we’ll merge into one super-galaxy. Springel sees this happening across the universe. For a while.
But the universe is expanding. Galaxies are drifting apart.
“Eventually, all the galaxies will stop merging.”
— Volker Springel
Isolated islands in the dark.
They’ll keep making stars until they run out of fuel. Then the suns will die. Go dark. The black holes will remain. The last survivors in a cold, empty sea.
Or so we think.
Fading Away
Stephen Hawking had a wild idea in 1974. Black holes die. They evaporate.
It sounds crazy. But quantum theory allows space itself to flicker with particles. Near the edge of a black hole—near that event horizon—some particles escape. Others fall in.
The escape drains energy. Mass leaves the black hole. Slowly. So slowly we can’t see it yet. But Hawking Radiation suggests they leak away over eons.
Size matters here. Small holes evaporate fast. Big holes? Eons and eons.
When the end comes, the smallest will vanish first.
Will supermassive holes do the same?
New theories say maybe not. Some physicists think “information” can’t be lost. Maybe the evaporation stops once half the mass is gone. Maybe the hole shrinks into a stable remnant. A black shell. A cosmic zombie. 🧟
They don’t know. None of us do.
What’s left in the end? Silence? A shell? Nothing at all?
The black holes keep eating. The universe keeps expanding.
And we just wait.
