Every Star That Could Destroy Earth Explained In 19 Minutes

[00:00:00]Betelgeuse. If you were to look up at Orion tonight, you would see a red star sitting on the hunter's shoulder, calm and orange and unremarkable.

[00:00:09]It has been there for as long as humans have had eyes.

[00:00:12]But that star is already dead. It just doesn't know it yet.

[00:00:17]This is Betelgeuse.

[00:00:19]It sits roughly 650 light-years from Earth. And it is a red supergiant so large that if you dropped it into our solar system, its surface would swallow Mercury, Venus, Earth, Mars, and reach out toward Jupiter.

[00:00:35]Our sun burns hydrogen slowly, patiently, over billions of years.

[00:00:41]Betelgeuse burns through elements like a man throwing furniture into a fireplace to stay warm.

[00:00:47]It has already exhausted its hydrogen.

[00:00:50]It moved on to helium, then carbon, then neon. Each stage burning faster than the last. Each stage buying it less time.

[00:01:00]When it reaches iron, the fire stops.

[00:01:02]Iron does not release energy when fused.

[00:01:05]It absorbs it. And when that happens, the core collapses in less than a second, falling inward at a quarter of the speed of light. And the star tears itself apart in a supernova bright enough to cast shadows on Earth at noon.

[00:01:21]In 2019, Betelgeuse began to dim. It faded by 35% over a few months. And for a while, astronomers genuinely wondered if they were watching the countdown.

[00:01:33]It turned out to be dust. A cloud of soot the star had coughed up and hidden behind.

[00:01:39]But the dimming revealed something worse.

[00:01:42]Betelgeuse is unstable, bloated, and pulsing irregularly like a heart that has forgotten its rhythm.

[00:01:49]At 650 light-years, a supernova would not sterilize us.

[00:01:55]It would light the sky for months and then fade.

[00:01:59]But our estimate of that distance has an error bar and the star may already have exploded with the light still crawling toward us across six centuries of empty space. Rigel.

[00:02:11]The same constellation has a second one.

[00:02:14]Down at the hunter's foot, opposite Betelgeuse, there is a blue-white star that most people never look at twice.

[00:02:22]And it is burning itself alive faster than almost anything else you can see with the naked eye.

[00:02:28]This is Rigel.

[00:02:30]It sits about 860 light-years away and it is a blue supergiant, roughly 20 times the mass of our sun and 120,000 times more luminous.

[00:02:42]Betelgeuse is old and swollen and visibly falling apart. Rigel is not.

[00:02:48]Rigel is still holding its shape, still burning white-hot, and that is exactly the problem.

[00:02:55]Stars this massive convert their fuel at a rate that borders on suicide.

[00:03:01]Our sun will last 10 billion years.

[00:03:04]Rigel has perhaps 8 million total and most of them are already gone.

[00:03:09]It will end the same way Betelgeuse will, in a core collapse and a supernova.

[00:03:15]And there is nothing in the physics that gives it a way out. The two brightest stars in the most recognizable constellation in the sky are both corpses waiting for the paperwork. Orion as you know it is temporary. Eta Carinae.

[00:03:31]In 1837, a star in the southern sky brightened until it became the second brightest object in the entire night.

[00:03:40]And then it stayed that way for almost 20 years.

[00:03:44]Sailors used it to navigate.

[00:03:46]Astronomers had no idea what they were watching.

[00:03:49]And then it faded, went quiet, and everyone moved on.

[00:03:55]This is Eta Carinae.

[00:03:57]It sits about 7,500 light years from Earth in the Carina Nebula, and it is one of the most massive and most violent stars we have ever found.

[00:04:07]The primary star weighs somewhere between 100 and 150 times the mass of our sun.

[00:04:14]Stars that large are not stable.

[00:04:17]They are barely holding themselves together against their own radiation, constantly on the edge of blowing their outer layers into space.

[00:04:25]In that event, now called the Great Eruption, the star ejected somewhere between 10 and 45 solar masses of material into space, more matter than most stars contain in total, and it did not die.

[00:04:39]It dimmed and kept burning.

[00:04:42]We still cannot fully explain it.

[00:04:44]Point a telescope there now, and you will not see a star.

[00:04:48]You will see a cloud shaped like an hourglass, two enormous lobes of gas expanding away from something buried in the middle.

[00:04:57]That is the debris, the Homunculus Nebula, still expanding outward at over a million miles per hour, and it is hiding whatever is happening inside.

[00:05:07]Eta Carinae is expected to end as a hypernova, an explosion so violent that it may collapse directly into a black hole and fire twin beams of gamma radiation out from its poles.

[00:05:20]The beams are the problem.

[00:05:22]A supernova radiates in all directions and weakens with distance.

[00:05:27]A gamma-ray burst concentrates its energy into two narrow cones, and inside those cones, the lethal range extends thousands of light years.

[00:05:37]Eta Carinae's rotation axis, as best we can measure it, does not point at Earth, but the star has already surprised us once, WR 104.

[00:05:48]If you were to watch this system in infrared over several years and stack the frames, you would see something that does not belong in astronomy, a spiral, a perfect glowing pinwheel of dust rotating slowly in deep space coiling outward like water going down a drain.

[00:06:07]Astronomers who first imaged it called it the Pinwheel Star.

[00:06:12]Then they measured which way it was facing.

[00:06:15]This is WR104.

[00:06:18]It sits roughly 8,000 light years away in Sagittarius.

[00:06:21]And it is not one star, but two locked in a tight 8-month orbit.

[00:06:26]One is a Wolf-Rayet star, a stellar corpse in progress.

[00:06:31]Wolf-Rayet stars are what remains when a massive star strips its own hydrogen envelope off and exposes the burning core beneath.

[00:06:40]They are the last stage before death.

[00:06:43]They blast stellar wind outward at over 4 million miles per hour and they lose more mass in a single year than our sun loses in a hundred thousand.

[00:06:53]The spiral is made of soot.

[00:06:56]As the two stars orbit each other, their winds collide and compress carbon into dust.

[00:07:02]And the orbital motion winds that dust into a coil like syrup poured onto a spinning plate.

[00:07:08]It is beautiful. It is also a diagram.

[00:07:12]A spiral is only visible as a spiral when you are looking at the orbit face-on, which means we are looking straight down the system's rotation axis.

[00:07:21]When the Wolf-Rayet star dies, if it produces a gamma-ray burst, the beam would fire along that axis.

[00:07:28]The initial measurements suggested we were within 16° of the line of fire.

[00:07:33]Later work has widened that number and muddied it. And the current estimates are less alarming.

[00:07:39]But nobody has been able to say with confidence that the barrel is pointed somewhere else.

[00:07:45]A gamma-ray burst at 8,000 light years would not incinerate the planet. It would strip the ozone layer in seconds, flooding the surface with ultraviolet radiation, killing the plankton at the base of the ocean food chain, and collapsing everything above it. The sky would turn brown from nitrogen dioxide.

[00:08:05]There would be no explosion, no sound, and no warning because the light announcing the star's death would arrive at the same instant as the radiation that kills you. IK Pegasi.

[00:08:18]Everything on this list so far has been thousands of light years away.

[00:08:22]This one is 150.

[00:08:25]It is faint, white, and unremarkable.

[00:08:28]And on a clear night, you could just barely find it with the naked eye.

[00:08:33]It is also the closest thing to a loaded gun that exists in our stellar neighborhood.

[00:08:38]This is IK Pegasi.

[00:08:40]It is a binary system, and neither star alone would matter.

[00:08:45]The first is a white main-sequence star, slightly larger than our sun, currently pulsing and unstable.

[00:08:52]The second is a white dwarf, the burned-out core of a star that died long ago, compressed into an object the size of Earth with more mass than our sun. A teaspoon of it would weigh several tons.

[00:09:06]White dwarfs are supposed to be endings.

[00:09:08]This one is a beginning.

[00:09:10]The two stars orbit each other every 21 days, close enough that they are almost touching by cosmic standards.

[00:09:19]When the larger star exhausts its hydrogen and swells into a red giant, its outer layers will spill across the gap, and the white dwarf will begin to feed.

[00:09:30]It will pull that gas onto its surface, growing heavier and heavier and heavier.

[00:09:36]There is a hard limit. At roughly 1.4 times the mass of our sun, a white dwarf cannot support itself anymore.

[00:09:45]The electrons holding it up surrender, and the entire star detonates in a single instant, converting itself into a type 1a supernova.

[00:09:56]Nothing survives.

[00:09:57]There is no core left behind, no neutron star, no black hole, just an expanding shell of debris.

[00:10:05]To sterilize Earth, a type 1a would need to be within about 3,000 light-years.

[00:10:11]IK Pegasi is at 150.

[00:10:15]But the system is moving, and by the time the white dwarf is ready, in perhaps a few hundred million years, it will have drifted to a safer distance.

[00:10:24]Probably. The uncomfortable part is not the timeline.

[00:10:28]It is that the closest supernova candidate we have ever identified is sitting 150 light-years away in a quiet corner of Pegasus, slowly assembling itself. Sagittarius A star.

[00:10:41]If you were to look toward the constellation Sagittarius on a summer night, you would be looking directly at it. There is nothing there. No glow, no shape, no light of any kind.

[00:10:52]It is the largest object within 100,000 light-years of Earth, and it is completely invisible. This is Sagittarius A star, the supermassive black hole at the center of our galaxy.

[00:11:05]It sits 26,000 light-years away and weighs 4.3 million times the mass of the sun.

[00:11:13]Every star you have ever seen, including our own, is orbiting it right now.

[00:11:18]Ours takes 225 million years to complete one lap.

[00:11:24]It has already made this trip about 20 times, and each time it does, the neighborhood is different.

[00:11:30]For a black hole its size, Sagittarius A star is remarkably quiet.

[00:11:36]It is eating almost nothing.

[00:11:38]Perhaps a hair's width of material falls in per second, which is why we cannot see it.

[00:11:43]Its cousins in other galaxies are not so restrained.

[00:11:47]They devour entire stars and the material spiraling and heats to millions of degrees, forming a disc that outshines every star in the host galaxy combined.

[00:11:59]Those objects are called quasars and they fire jets of plasma thousands of light-years into space.

[00:12:07]Sagittarius A star was one of them once and the evidence is still there.

[00:12:13]Above and below the galactic center sit the Fermi bubbles, two structures of hot gas extending 25,000 light-years in each direction glowing in gamma radiation.

[00:12:24]They are scar tissue.

[00:12:26]Something at the center of our galaxy erupted a few million years ago and the wound has not healed.

[00:12:33]The black hole is not going to swallow Earth.

[00:12:36]We are far too distant and its gravity at this range is no different from any other object of that mass.

[00:12:43]The danger is that it can wake up.

[00:12:46]All it requires is one star wandering too close, one gas cloud falling in the wrong direction and the center of the Milky Way lights up again, flooding the galaxy with radiation from an object we cannot see, cannot predict, and cannot move away from. Gliese 710.

[00:13:05]There is one star in the sky that is aiming directly at us and it is the most boring object you will ever see.

[00:13:13]A small orange dwarf sitting 62 light-years away in the constellation Serpens Cauda.

[00:13:21]Cooler than our sun, dimmer than our sun, roughly half its mass.

[00:13:26]It will never explode.

[00:13:28]It will never produce a gamma-ray burst.

[00:13:31]It will simply burn quietly for another 50 billion years.

[00:13:35]And it is coming here.

[00:13:37]This is Gliese 710.

[00:13:40]Every star in the sky is moving, drifting through the galaxy on its own trajectory.

[00:13:46]And most of them are moving sideways relative to us.

[00:13:51]Gliese 710 is not.

[00:13:54]It is heading almost directly toward the solar system at about 32,000 miles per hour.

[00:14:00]And because it is coming straight at us, it appears nearly motionless in our sky.

[00:14:06]It is the one star we can see that is aiming for us.

[00:14:09]And it looks like the one star that isn't doing anything at all.

[00:14:14]For decades, its path was a guess.

[00:14:17]Then, the Gaia spacecraft measured the positions and motions of nearly 2 billion stars with a precision nobody had ever achieved.

[00:14:26]And the guess became a schedule.

[00:14:29]In roughly 1.3 million years, Gliese 710 will pass within about 0.16 light-years of the sun.

[00:14:37]That is 10,000 astronomical units.

[00:14:41]That is closer than any star we know of has come in the history of our species.

[00:14:46]And it is deep inside the Oort Cloud.

[00:14:49]The Oort Cloud is the reason this matters.

[00:14:52]Beyond Neptune, beyond the Kuiper Belt, there is a vast spherical shell of frozen debris surrounding the entire solar system.

[00:15:01]Trillions of icy bodies drifting in the dark, so far out that the sun holds them with almost no strength at all.

[00:15:08]They are barely attached.

[00:15:10]A passing star does not need to hit anything.

[00:15:13]It only needs to walk through the room and disturb the air.

[00:15:17]As Gliese 710 crosses through, its gravity will nudge those objects off their orbits, and some fraction of them will fall inward.

[00:15:27]Not immediately.

[00:15:29]The comets will take hundreds of thousands of years to make the journey down toward the inner solar system, arriving long after the star has moved on. Estimates suggest the impact rate on the inner planets could rise by a factor of 10, sustained for a million years or more, a slow drizzle of ice and rock falling out of the dark with no pattern and no source anyone alive would be able to see.

[00:15:55]Nothing on this list is quieter.

[00:15:58]There is no explosion, no radiation, no visible event.

[00:16:02]A dim orange star will drift through the outer edge of our system, brighten in our sky until it becomes the brightest star anyone has ever seen, hang there for a few thousand years, and then move on.

[00:16:16]It will not touch us.

[00:16:18]It will just knock something loose on its way past, and then leave the solar system to deal with the consequences for the next million years. The sun.

[00:16:27]It is there right now. It has been there every day of your life, every day of your parents' lives, and every day of every life that has ever existed on this planet.

[00:16:37]It is the reason all of it happened.

[00:16:39]It is also the reason none of it will last.

[00:16:42]This is the sun. It is 93 million miles away, and it is currently in the calmest, most stable phase of its existence. It has been fusing hydrogen into helium for 4.6 billion years, and it has roughly 5 billion left.

[00:17:00]But that number is misleading, because the sun does not wait until the end to kill us.

[00:17:05]It is getting brighter. As helium accumulates in the core, the core contracts, heats, and burns faster.

[00:17:13]The sun today is about 30% brighter than it was when Earth formed. And it gains roughly 1% every 100 million years.

[00:17:23]In about a billion years, that increase will be enough to push Earth past the point where liquid water can survive on the surface.

[00:17:31]The oceans will evaporate.

[00:17:33]The water vapor will trap more heat, which evaporates more water, which traps more heat. And the planet will run away into a greenhouse state and become Venus.

[00:17:44]Life on Earth ends a billion years from now, with the Sun still looking almost exactly as it does today.

[00:17:52]The real death comes later.

[00:17:54]When the hydrogen in the core finally runs out, the core collapses and ignites a shell of hydrogen around it. And the Sun swells.

[00:18:03]It will expand past Mercury, past Venus, and out to roughly the orbit of Earth, becoming a red giant a hundred times its current size, and thousands of times brighter.

[00:18:15]Whether it physically swallows the scorched rock we used to live on is still debated, and it does not matter.

[00:18:22]Then, it will shed its outer layers into space, a slow exhale over tens of thousands of years, leaving behind a planetary nebula that will glow for a while and then disperse.

[00:18:34]What remains in the middle will be a white dwarf, the size of Earth, dense beyond comprehension, holding no fuel and generating no light of its own.

[00:18:44]It will cool for trillions of years.

[00:18:47]Every star on this list is a threat because of what it might do.

[00:18:52]The Sun is different. It is not a possibility, or a probability, or a candidate. It is the star that will destroy this planet. It is doing it right now, slowly and quietly. And it is the same one you have been thanking for the warmth on your face every morning of your entire life.