The Universe's SECRET Weapons and How they Affect Earth! | How the Universe Works | Science Channel

[00:00:06]Say you've got a taste for adventure. A risktaker extraordinaire used to laughing at danger and death. Want to take on the worst the universe can throw at you? Better think twice. The cosmos has it all. Havens for life and lethal hell holes. Our universe is both benevolent and violent.

[00:00:37]There are little oasis pockets where things are very nice and calm and really good for life, like right around here.

[00:00:43]But there are definitely places and times where things get violent and rough.

[00:00:51]But you don't have to venture to the wrong side of the tracks to encounter some of the universe's scariest locations.

[00:00:59]Some are right in the neighborhood.

[00:01:03]Take Beetlejuice, hidden amidst the beautiful Orion constellation, a red star 640 light years away from Earth and ready to die.

[00:01:16]Now, Beetlejuice is a huge red super giant star, and it even looks kind of angry and red hanging up there in the sky. It's so big that if you put it in our solar system, it would expand all the way out to the planet Jupiter.

[00:01:28]It's gigantic.

[00:01:31]>> When massive stars like Beetlejuice die, they go out with an epic bang.

[00:01:38]>> Now, this star is just on the edge of going supernova. And when it does, we're in for quite a show.

[00:01:46]Beetlejuice is running out of gas.

[00:01:50]The nuclear fire at its heart fights a constant battle against the crushing gravity of its enormous mass.

[00:01:58]Once the gas is gone, you'd better stand back. No one can predict exactly when, but soon the star will begin to collapse.

[00:02:10]Imagine you're near the surface of this star just before it goes out. Just before it goes supernova, you're going to see the surface of that star just recede away from you incredibly rapidly.

[00:02:19]Much like if you were at the beach and you saw the water just recede away from you really rapidly, you know something bad is coming.

[00:02:28]The collapsing outer layers pummel the core, making it denser and denser. The core compresses as more of the star falls in. All that gas has to go somewhere. And so it bounces with an explosive force we can hardly imagine.

[00:02:52]When Beetlejuice goes supernova, we are talking about an epic catastrophe. An entire star is exploding.

[00:03:01]It's hard to describe just how much energy that is.

[00:03:06]Imagine all the energy the sun puts out every second. Multiply that times 31 million seconds in a year. Multiply that by 10 billion years in the sun's lifetime.

[00:03:18]That is how much energy a supernova puts out.

[00:03:24]The energy unleashed is a shockwave of light, heat, and superheated gas racing out at thousands of miles a second, destroying everything around it.

[00:03:37]>> Life on any planet orbiting this exploding star would be completely eliminated.

[00:03:44]You certainly wouldn't want to book a cruise to Beetlejuice anytime soon or after it has gone supernova.

[00:03:56]Because when it finally dies, it might leave a nasty surprise. One of the most extreme objects in the universe, a neutron star.

[00:04:06]>> Neutron stars are kind of like vampire zombies. They are the cores of massive stars that have died. But now these neutron stars have their own gruesome lives. And you don't want to get anywhere near this thing.

[00:04:21]>> Trillions and trillions of tons of matter are compressed into a sphere roughly the size of Manhattan.

[00:04:29]A neutron star is the densest body we know of in astrophysics besides a black hole. So, if you somehow had a little stonesized piece of neutron star matter, it would weigh 100 million metric tons and it would immediately fall right through your hand.

[00:04:51]>> Because the neutron star is so dense, it generates an intense gravitational field.

[00:04:58]>> It is really hard to exaggerate how dramatic and dangerous a neutron star is. The gravity is so intense it would actually bend light around it. You would see all these kind of weird shimmering effects.

[00:05:14]Dazzling, but deadly. No astronaut will ever be able to approach a neutron star.

[00:05:21]But if you're an armchair traveler and want to find out what would happen, let's send a galactic crash test dummy.

[00:05:28]We'll call him Chuck.

[00:05:32]Crash test dummies are a species that are completely devoted to ensuring human safety and they sacrifice themselves to do it.

[00:05:43]>> Everything he encounters is going to be it's going to be a pretty rough ride.

[00:05:47]Better him than me.

[00:05:52]>> As Chuck nears the neutron star, its gravitational grip is doing very bad things.

[00:06:01]The gravity is pulling on him so hard that he is accelerating all the way down to the surface. He'll be moving at very roughly 1/2 to 2/3 of the speed of light. The neutron stars gravity is 200 billion times stronger than on Earth.

[00:06:17]Around 150 mi above the surface, it starts to pull on Chuck's limbs in a distinctly unpleasant way.

[00:06:27]As you get closer and closer to a neutron star, we were told to think that it would be this elegant spaghettification where you would get longer like a piece of spaghetti. But in reality, you're going to get ripped to shreds.

[00:06:39]Think about what you're really going to experience. Think about first all your joints dislocated in your body, your skin getting ripped off of your body, your bones being pulled apart, your organs being pulled apart.

[00:06:55]Within a blink of an eye, our dummy is just a thin stream of atoms hurtdling towards the star.

[00:07:02]>> Those atoms will eventually fall down onto the neutron star. And unfortunately, the violence doesn't stop there.

[00:07:10]>> What's left of Chuck hits the surface, triggering a huge burst of energy.

[00:07:16]>> So, we're talking about 100,000 miles per second. That's an impact. He's going to hit so hard that the amount of energy released is just huge. It would completely dwarf the entire arsenal of nuclear weapons on our planet.

[00:07:32]>> Anything and anyone that ventures too close to a neutron star is destined for this catastrophic end.

[00:07:41]>> A neutron star is one of the most dangerous objects you can meet in any phase of their existence. If you're meeting a neutron star right when it's born, that means you're very near a supernova. and that means death. If you meet a neutron star after the supernova has gone off, that would be death. And then if you were lucky enough or unlucky enough to go falling onto a neutron star, uh you'd be destroyed very rapidly and torn apart.

[00:08:06]If I had one piece of advice about neutron stars for future space travelers, it would be no. No, stay away.

[00:08:17]So, you really don't want to be anywhere near one neutron star and its lethal gravity.

[00:08:26]Try two neutron stars colliding and creating one of the strangest and most lethal particles in the universe.

[00:08:44]Some of the brightest lights in the universe are created by young blue stars as they die in bright explosions.

[00:08:55]Super luminous supernovas are the ultimate example, but other types of stars can go supernova, too.

[00:09:02]Yellow stars like the sun swell up as they age, transforming into oversized monsters known as red giants.

[00:09:13]The biggest of these bloated stars are called red super giants.

[00:09:17]And astronomers often see them explode in bright, violent supernovas.

[00:09:24]The bigger the red giant, the bigger the bang. But there's a problem.

[00:09:30]Nobody has ever witnessed the flash of the very biggest red super giants in our galaxy. These most massive of bloated old stars have to be dying. But if not in a flash of light, then how?

[00:09:46]Now, scientists have come up with an extraordinary theory.

[00:09:50]Instead of exploding in a bright supernova, the biggest of the red super giants are simply blinking out of existence.

[00:09:59]Scientists dubb these weird disappearing deaths unnovas. And new evidence suggests these unnovas could be coldblooded planet killers.

[00:10:11]You're looking up into the sky, the sun is shining, then all of a sudden it just turns out that's what an unnova would look like.

[00:10:20]>> It would be the biggest catastrophe in the history of the planet. Life as we know it would not be able to survive.

[00:10:27]>> Scientists believe the key to the biggest red super giants disappearing is a super efficient transformation from a giant burning ball of gas to a tiny dense black hole.

[00:10:41]Everything has to be perfectly tuned to get an ANOVA. The star can't be rotating very quickly and the outer layers can't expand much. When all the conditions are right, it just collapses into a black hole.

[00:10:52]>> They basically just become a black hole.

[00:10:57]>> It's not unusual for red super giant stars to form black holes when they die, but most do it after they've released the violent flash of light we see as a supernova.

[00:11:09]But the biggest super giants have so much mass and so much gravity in their cores that when they collapse, not a single photon of light escapes from the newly formed black hole.

[00:11:22]To an observer, the star simply disappears. The death of a star without the flash, an unnova.

[00:11:31]>> It's almost like the star has fallen in and has forgotten to come out. But more realistically, what's going on is when it falls in, it just can't come out.

[00:11:40]It's created so much gravity around itself that even an explosion doesn't allow it to escape. It doesn't get to explode. It just falls right into a black hole. So, what makes UNOVAs planet killers? The biggest red super giants age relatively quickly, dying after just 10 million years. But astronomer David Kipping believes that just might be enough time for these giant stars to create potentially habitable worlds.

[00:12:09]Planets can form pretty quickly. They can form in within a million years around these stars. So there should be time for these massive stars to form planets. And in fact, when we look at the remnants of massive stars, we indeed find rocky planets around them. So as far as we can tell, these stars really should have worlds orbiting them.

[00:12:28]Imagine a lone rocky world warmed by the far distant light of a red super giant star.

[00:12:39]Simple life clings to shallow rock pools on the young planet's surface. But their warm, comfortable existence is doomed.

[00:12:48]High in the sky, the far distant super giant sun is burning through the last of its hydrogen fuel. The force of gravity pushing in overcomes the force of fusion pushing out.

[00:13:02]And 20,000 trillion trillion tons of hot burning hydrogen gas collapses down into a single point in space, a black hole.

[00:13:17]Surprisingly, the black hole that makes the UN nova so dark doesn't put the planet in immediate danger. This is one of the biggest misconceptions of movies is that suddenly if a star becomes a black hole, then the planet is going to be sucked into it. The gravity of the black hole is exactly the same as the gravity of the star as long as it hasn't lost any mass. From a distance, if you're orbiting the star, it's the same as orbiting the black hole. Nothing would change.

[00:13:44]>> As the super giant star collapses, the view from the far distant planet would be surreal.

[00:13:51]What you're going to see is there's your star in the sky and then a minute later it's gone. You will actually see it collapse forming a black hole and the whole thing just falls into it and that's that. What would happen next would be a long slow cold death. You're basically turning off your star.

[00:14:09]A fleeting moment but the beginning of a winter that would never end.

[00:14:15]If you suddenly turned off the light from the sun, life wouldn't actually be immediately extinguished. It would just be like the night. We would be a little bit cooler than normal. But eventually, over time, over weeks, over months, over years, the planet would begin to freeze over.

[00:14:33]>> After 100 years, a global ice age engulfs the planet. First the land, then the oceans.

[00:14:42]>> The oceans would freeze over into a thick crust. Maybe a little bit of liquid water would still be there at the bottom of the ocean warmed by volcanic vents.

[00:14:50]>> Eventually, what you're left with are things that don't depend on sunlight to live. Maybe there are tube worms living in in vents, cracks, hydrothermal vents in the bottoms of the oceans and that sort of thing. But even those can't possibly live forever.

[00:15:06]The internal heat of the planet continues to radiate out into space. The surface temperature drops below - 350° F and the atmosphere collapses onto the surface as snow. The core of the planet can no longer support active geology.

[00:15:26]All life is gone. The planet is dead.

[00:15:32]>> So these habitable worlds will eventually end up being just these spheres of ice.

[00:15:40]Whether killed by the light of a supernova or by the darkness of an unnova, planets are in the firing line from killer stars. But research recently released suggests that stars too can fall victim to murder. And some of these killings are straight out of a horror movie.

[00:16:02]How can an old star that's on the way to die get more mass so it can become young again? Well, it can do exactly what a vampire does. It can suck life from something else.

[00:16:22]2012, the Hubble Space Telescope makes a gruesome discovery. It finds killer stars sucking the life from their neighbors.

[00:16:34]These vampire killers are found lurking inside tightly packed groups of stars known as clusters.

[00:16:43]>> Stars are born in giant clouds of dust and gas. And these clouds have enough material to make dozens or even hundreds of stars. We call these family of stars star clusters. And we think they're all roughly the same age.

[00:16:59]Young clusters shine like jewels with an array of bright colors, blues and yellows and reds.

[00:17:07]But this starry rainbow changes over time. The blue stars disappear first.

[00:17:14]These are the biggest stars in the cluster, burning brightly and dying young after millions of years. Next to go are the yellow stars. These medium-sized stars age over billions of years, gradually turning red like ripening fruit. After 10 billion years, the entire cluster matures to a deep red. This gradual shift in color is useful to astronomers because it allows them to judge just how old a cluster is.

[00:17:47]When you look at a population of stars in one place, if you see a lot of blue stars, you can be pretty confident that that must have young stars. They couldn't have been born too long ago because blue stars are massive and massive stars go through their fuel quickly and live very short lives.

[00:18:06]But in the 1950s, astronomers spotted something seriously weird in an ancient cluster. Tucked amongst the old red stars, they found a handful of brightly shining young blue stars. New stars don't usually form inside mature clusters. So, how did they get there?

[00:18:26]The only explanation, somehow the old stars were getting younger. Astronomers dubbed these agedefying stars blue stragglers.

[00:18:38]In some clusters, we see these blue stars that appear younger than they should. In some ways, they're kind of straggling behind the natural aging of the cluster. Something must be actively rejuvenating a star. But what could do that?

[00:18:51]>> If you imagine these blue straggler stars were people in a crowd. These stars would look like they had been given a facelift. They're masquerading as younger stars when really they're just as old as everybody else in the room.

[00:19:04]Astrophysicist Natalie Gosnell believed the blue stars were being rejuvenated by a fresh supply of hydrogen fuel. But where was it coming from?

[00:19:16]In 2015, Natalie took a closer look at the Hubble images of the blue straggler cluster. She discovered that most of the younglooking stars were in binary partnerships with the corpses of dead stars that appeared to have had their gas sucked away from them.

[00:19:34]>> So in movies, vampires are perpetually youthful because they are sucking blood from humans. And so in this case, we have stars that are sucking gas and material from other stars, keeping them looking young.

[00:19:56]Right now, somewhere in the universe, a giant star is detonating, creating a huge cosmic explosion called a supernova.

[00:20:13]Supernovas are a big giant dramatic end to a star's life.

[00:20:24]All stars die, but only the biggest go out with a bang.

[00:20:29]For a star to go supernova, we think it has to be at least eight times more massive than our sun.

[00:20:35]>> It's so easy to think of our sun as this incredibly gigantic thing. But our sun is absolutely tiny compared to some of the giant stars in the sky.

[00:20:50]We can see some of these giant stars with the naked eye.

[00:20:55]And the 10th brightest in the night sky is a red super giant around 15 times the mass of the sun.

[00:21:04]Beetlejuice.

[00:21:07]Beetlejuice is so big that if you were to place it in our own solar system, it would stretch to the orbit of Jupiter.

[00:21:17]This is one of the biggest beasts in the galaxy. It's a star also that is on the verge of death.

[00:21:25]>> Beetlejuice is less than 10 million years old.

[00:21:29]But this huge stars days are numbered.

[00:21:33]It's ready to blow.

[00:21:38]And when it does, we'll see a region of sky brighten for 14 days until it's nearly as bright as a full moon.

[00:21:47]It is going to be one of the most spectacular shows in history.

[00:21:54]And it could happen at any moment. I mean, this is the thing. I often stand outside in my yard in the wintertime. I look up at Orion and I see Beetlejuice and I'm like, explode.

[00:22:05]So what will make Beetlejuice go supernova? To understand a giant star's death, we need to understand its life.

[00:22:17]From the day it's born until the day it dies, a star's life is a constant battle.

[00:22:26]Gravity is pulling in and energy pushing out.

[00:22:31]The interior of a star is fusing countless atomic nuclei together.

[00:22:36]>> Atoms are ramming into each other, getting very, very close.

[00:22:41]And if they get close enough, they'll actually stick and form a larger atom.

[00:22:46]>> Every second, a giant star fuses 7 12 billion tons of hydrogen.

[00:22:52]>> That amount of energy is roughly equivalent to about 100 billion atomic bombs per second.

[00:22:59]That's a big ass explosion.

[00:23:03]>> This explosive energy threatens to blow the star apart.

[00:23:09]But the stars own massive gravity keeps the lid on.

[00:23:13]>> Everything in the universe is a fight between the inward force of gravity and the outward force of pressure or energy.

[00:23:21]>> Every single star in the sky, even our own sun, is an incredibly dynamic battleground. In many ways, stars are an explosion that are actually too big to explode. Gravity holds it together.

[00:23:33]>> This battle between these two opposing forces determines the life and death of the star. And this is where size matters. The more massive the star, the more gravity pushes inward and the harder the star has to push outward to keep itself alive.

[00:23:55]Very massive stars are like stars on steroids.

[00:24:00]They have a lot of fuel to burn. They're so powerful that they use up their fuel at a rapid rate.

[00:24:10]Massive stars like Beetlejuice are giant factories fusing lighter elements into heavier ones. But the hard work doesn't start until their final years. For around 90% of their life, they fuse hydrogen into helium. But eventually, the hydrogen starts running out.

[00:24:32]In the core of a super giant star, there's a sequence of fusion that goes from lighter elements to heavier elements, and it gets faster and faster every step of the way.

[00:24:42]The countdown to death begins.

[00:24:46]The inward push from gravity takes over, raising the temperature in the core.

[00:24:52]Helium starts fusing into carbon.

[00:24:55]There's enough helium to last about a million years, but it too runs out and things start speeding up. Carbon gets fused into neon. That takes about a thousand years. Neon fusing into silicon, that takes about 1 year. Once it starts fusing silicon into iron, that takes one day.

[00:25:17]It gets more and more frantic. It's It's kind of like a cooking contest show whereas the clock is running down.

[00:25:22]They're trying to do more and more things and they get more and more frantic until ding, time's up.

[00:25:31]>> The star is now in its death throws.

[00:25:34]>> Once iron production has started, the clock is ticking towards the cataclysmic end of this star.

[00:25:44]A giant ball of incredibly dense iron forms in the middle of the dying stars core.

[00:25:52]This iron sphere is several thousand miles across and unbelievably hot.

[00:25:59]It gets so hot there, the temperature almost becomes meaningless. I mean, we're talking about a billion degrees in the center of one of these stars.

[00:26:11]This extreme heat is caused by fusion reactions. More and more reactions create heavier and heavier elements. And with each step, less and less energy is produced until iron is created. When you try to fuse iron nuclei together, that takes energy. It doesn't generate energy. So once the core starts to fuse iron, it's basically stealing its own energy.

[00:26:38]The growing iron core sucks more and more energy from the star. Gravity continues pulling in, overwhelming the outward pressure from inside the star.

[00:26:52]Everything gets crushed to unimaginable degrees. All of a sudden, there's no nuclear reaction to support the star against the crush of gravity.

[00:27:04]With nothing left holding it up, the star is doomed. Gravity wins. The edges of the iron core collapse. Trillions of tons of dense iron fall inward at a quarter of the speed of light. The star has now less than 1 second left to live.

[00:27:24]Things start to fall apart really quickly.

[00:27:28]The core collapse is so fast that the outer layers of the star don't even have time to react. They're just hanging there. It's kind of like wy coyote when a cliff collapses underneath him and he doesn't even fall until he notices.

[00:27:42]>> The rest of the star collapses. A trillion trillion trillion tons of gas hurtle inwards following the iron.

[00:27:51]>> Think about the entire mass of a star that has been held up by nuclear reactions inside. All of a sudden, those nuclear reactions go away in a split second. Everything rushes into the middle and that sets off the most dramatic explosion in the universe.

[00:28:15]The spectacular death blow can outshine all of the stars in the galaxy.

[00:28:22]But there's a problem. We still don't fully understand how a collapsing ball of iron and tons of falling gas create a giant fireball.

[00:28:34]How this collapsing core triggers a massive explosion is one of the biggest mysteries in astrophysics.

[00:28:46]>> For over 4 and 1/2 billion years, the sun has bathed our home planet with light.

[00:28:54]Its bright, stable glow helps life flourish.

[00:28:59]But hidden in the night sky, other planetary systems haven't been so lucky.

[00:29:06]>> Hanging right above your head every night, we see up there these dead corpses of stars.

[00:29:13]>> 400 light years from Earth lies a system called SDSS J1228.

[00:29:20]A disc of debris orbits the faintly glowing leftovers of a dead star.

[00:29:27]J1228 is a dead star. It is the core of a star that had aged, blown off its outer layers, revealed the core, which is about the size of the Earth, but has about half the mass of the star in it.

[00:29:38]And we call these white dwarfs.

[00:29:48]May 2018, astronomers investigated J1228 using the world's largest optical telescope, the Grand Telescopio Canarius.

[00:30:01]They discovered what appears to be a ball of iron orbiting the white dwarf.

[00:30:07]The lump of metal less than 400 m across could be the exposed core of a destroyed planet.

[00:30:16]It's a clue to this system's past.

[00:30:20]>> It's always a little poignant when you see evidence of a planet around a dead star. You know, you think back of when that star was shining and could there have been life in that solar system?

[00:30:29]>> The J1228 system is a cosmic graveyard.

[00:30:34]It might look different than our solar system, but this is our future.

[00:30:41]This discovery of a dead planet orbiting a dead star is like looking into a crystal ball. And is it the future of our own solar system? Yep.

[00:30:52]>> For a glimpse into your future, you know, all you need to do is look up.

[00:31:00]>> Just like J1228, our son will die, killing off Earth in the process.

[00:31:09]This terrifying fate will play out across the galaxy in a star apocalypse.

[00:31:16]>> Our sun is a fairly common type of star in the Milky Way. And so other stars in the Milky Way will undergo the same sort of fate as the sun and will end up as white dwarfs. And so any other planets out there orbiting sunlike stars will undergo a similar fate.

[00:31:34]>> Once the stars like our sun have died out, what's going to happen? Could life still survive around white dwarfs?

[00:31:41]>> To understand the fate of sunlike stars, we have to look inside them. Buried within are clues to how they live and why they die. The core, the very center.

[00:31:53]That's where the action is. That's where the star is fusing light elements into heavier elements. That works like a like a hydrogen bomb. That's the same thing.

[00:32:03]If you compress hydrogen enough, it gets very hot and the pressure gets very high and it fuses into helium and generates energy, heat. And that's what's happening in the core of every star.

[00:32:15]Because of their enormous mass, stars have huge amounts of gravity.

[00:32:20]This gravity pushes inwards trying to collapse the star.

[00:32:25]But fusion energy from the core stops that from happening.

[00:32:31]It's really this sort of very balanced dance between gravity pushing in, fusion energy pushing out.

[00:32:38]>> You can think of a star as losing energy continuously to the outside world and gravity is saying, "Yes, I'm going to take over." But no, the nuclear reactions inside a star replenish the energy that's lost and keep the star hot and pressurized inside so that the pressure, gravity, balance can be maintained.

[00:33:03]>> This balance keeps sunlike stars alive for up to 10 billion years until the stars gas tank runs dry.

[00:33:14]It's going to run out of fuel. And when that happens, it's going to die. But what is that going to look like? How is this going to happen?

[00:33:24]100 million years ago, things in the J1228 system started to get ugly.

[00:33:32]First, the star grew large.

[00:33:35]Really large.

[00:33:37]Once the center starts fusing heavier elements, the outside will swell into what will eventually be a red giant star. J1228 transformed into a red giant.

[00:33:51]Its outer layers blew off, extending out over 40 million miles.

[00:33:57]When stars like our sun die, it's not a quiet affair. It's very violent and ugly and messy. They turn into red giants and they turn themselves inside out and vomit all over the solar system.

[00:34:12]>> When J1228 swelled into a red giant, nearby planets were stuck in a kill zone.

[00:34:21]The dying star engulfed them or fried them with temperatures of over,200° F.

[00:34:28]Atmospheres disappeared. Oceans boiled away.

[00:34:34]But one planet survived J1228's death throws.

[00:34:38]>> Here's a case where a planet survived in some sense the death of its own star and is still hanging around, still hanging on, hoping for something new.

[00:34:51]>> The red giant's expanding outer layers separated from the stars core.

[00:34:58]With no active fusion, the core collapsed into a white dwarf.

[00:35:04]The white dwarf's dense gravity then went to work on the one surviving planet.

[00:35:11]A planet that might have been orbiting the normal star can gradually spiral in toward the white dwarf and then eventually the gravity of the white dwarf pulls on the near side of the planet more than on the far side and that tears it apart.

[00:35:27]What we're seeing here is a dead star dining on its own solar system.

[00:35:35]That's what is in the future for the sun.

[00:35:41]J1228 feasted on the remains of its rocky worlds, leaving behind a disc of debris and the planetary core.

[00:35:52]It's a glimpse of Earth's future.

[00:35:56]What happened here around this white dwarf is going to happen to Earth. It's going to be stripped of its atmosphere, its crust, and its mantle. And the only thing that will remain will be the core.

[00:36:09]Fried and ripped apart by a dying star.

[00:36:12]Not a good way to go.

[00:36:15]Fortunately, for life on Earth, our own sun isn't dying just yet. The sun is middle-aged. It's 4 and a half billion years old and it's going to go on for another five or six billion years.

[00:36:27]>> We've got a little bit of time before our sun pukes all over the solar system.

[00:36:34]>> Our home planet may be safe for now, but systems like J1228 show us that sunlike stars are destined to die, killing off any life orbiting them. But sunlike stars aren't the only stars dying across the cosmos. There are others out there, and they're all doomed.

[00:36:58]There's a wonderful rainbow of stars out there of all different shapes, all different sizes, and all different colors.

[00:37:06]>> We're talking down to, you know, fractions of the mass of the sun up to hundreds of times the mass of the sun.

[00:37:13]>> When it comes to the star apocalypse, size matters. The bigger and brighter the star, the faster it dies.

[00:37:28]The Bearing Sea asteroid blew up in the atmosphere, but the Behringer crater asteroid hit the ground intact with its full force.

[00:37:40]Why do different asteroids behave differently? And what will AFUS do when it heads our way?

[00:37:49]Arosibo's radar may have the answer.

[00:37:53]>> When we bounce radar waves off of these objects, we can get effectively imagery of the surface of of some of these small objects uh that we just cannot do with optical telescopes.

[00:38:05]>> This is the radar image of a PFUS. It's so far away that all they could image were a few pixels.

[00:38:14]So this is our most recent radar image of asteroid AOS and you can see it's only a few pixels but it does give us information on what it actually is.

[00:38:29]>> These few pixels are enough to work out how big a pus is.

[00:38:35]From this image, we can constrain the size to be about 1,00 ft, which is about the same size as the receiver radio telescope. All of that from a weird bunch of pixels.

[00:38:55]Knowing the size and mass of an asteroid is critical to understanding what an asteroid is made of.

[00:39:02]If we have the size and the mass, we get the density. If we have the density, we know what it's made of. Rock has some density. Metal has a different density.

[00:39:12]So, we can determine a huge amount about the asteroid simply by pinging it with radar.

[00:39:20]Arosibo's data reveals that not all asteroids are alike.

[00:39:26]There's not just one kind of asteroid.

[00:39:28]There actually several kinds. And this is important to understand because they behave differently. They behave differently if they impact us and they behave differently if we're trying to prevent them from impacting us. We need to know what these asteroids are made of if they're going to hit the Earth because that drastically alters the potential effects.

[00:39:49]>> Asteroids come in different shapes, different sizes, and different compositions. And we think that is because they are the leftovers of planet formation. To understand how each asteroid formed and their threat level, we have to go back 4.6 billion years to the start of the solar system.

[00:40:09]>> The reason that there are all these asteroids floating around in our solar system today is just because of the early violence of the solar system as it was forming.

[00:40:21]>> At the birth of the solar system, the sun ignites, leaving a disc of gas and dust.

[00:40:32]Slowly over time, planets form.

[00:40:36]Lots of planets.

[00:40:39]>> The early solar system was a messy place. There were a lot more planets, a lot more forming planets. They would crash into each other. They would merge.

[00:40:48]They would disintegrate. They would reform.

[00:40:54]This process of accretion of building planetary worlds was not just you know kind of gentle and happy. It was it was violent.

[00:41:03]It was like a giant cosmic game of pool planet smashing into planet.

[00:41:12]The leftovers from this violence formed a ring of junk between Mars and Jupiter.

[00:41:18]>> And now we call that junk asteroids.

[00:41:21]They're just basically rubble left over from the formation of the solar system.

[00:41:29]Rocky leftovers became sea type or condrite asteroids.

[00:41:36]They're quite dense, so big ones can punch through the atmosphere and hit the ground.

[00:41:44]Radar reveals a rarer type of asteroid.

[00:41:49]Some of them really stand out because their density is so much higher than the rest of the other asteroids.

[00:41:56]>> These asteroids are M type or metal.

[00:42:02]Because their mass is great, they carry more kinetic energy during a strike.

[00:42:08]By far the worst one is this iron meteorite. This is really heavy. So, the difference if you were being hit by this, it would be the difference between being hit by a rock and being hit by a metal hammer.

[00:42:23]We think that both the Behringer and the KPG dinosaur killer were caused by metal asteroids.

[00:42:33]But there's another, more mysterious type floating through space.

[00:42:44]December 2018, NASA's spacecraft Osiris Rex approached the near-earth asteroid Bennu.

[00:42:53]>> Over time, it drifted out of the main asteroid belt, made its way into the inner solar system until it became a near-Earth asteroid accessible for our spacecraft to go and visit.

[00:43:04]Osiris trained its camera on Bennu.

[00:43:14]One of the biggest surprises on arrival of Bennu was the large number of large boulders on its surface. Bennu is really littered with huge boulders and littered with medium-sized boulders and littered with small boulders.

[00:43:27]>> Bennu is not a solid lump of rock. It's made up of thousands of bits of rock forming what we call a rubble pile.

[00:43:36]>> These asteroids aren't big singular spherical balls of rock, but rather they're literally piles of rubble.

[00:43:43]They're all sorts of pieces and fragments from another asteroid that had previously been disrupted that have all come back together and formed literally a pile of rocks held together by their own gravity.

[00:43:54]>> We think rubble piles formed from collisions inside the asteroid belt.

[00:43:59]Each impact blasted bits off. Then over time they came back together to form a loose pile of rocks.

[00:44:08]>> Imagine taking a big cosmic dump truck full of of of gravel and rubble and dumping it out there into space and letting gravity weakly hold it together.

[00:44:20]>> When scientists probe deeper into Bennu, they found another surprise. It's full of holes like Swiss cheese.

[00:44:28]If you could slice open one of these asteroids, you'd see there are a lot of voids. And in fact, 60% of what we're looking at is a void space. So, they're actually really fluffy. So, even though they're made of rocks, they're sort of the lint of rocks.

[00:44:44]>> Bennu helps us understand aus. Radar data shows that Apous is also a rubble pile.

[00:44:52]>> If you look at Apous, we really want to know how its orbit will evolve in the future. What we learn at Bennu about similarsized rubble pile asteroids might help us understand the future of an asteroid like Apous.

[00:45:04]>> So what would happen if the rubble pile called a P ofus hits Earth?

[00:45:08]>> You probably don't want that to hit you still, but it definitely makes it a lot weaker than something like a solid rock or even more a chunk of nickel iron metal.

[00:45:19]>> Does its composition make it any less of a threat?

[00:45:23]A rubble pal like a pulus is especially unnerving because we don't know when it interacts with the atmosphere if it's going to stay as one solid piece. Will it break up?

[00:45:33]When these rubble piles start interacting with planets, if they fly near a planet, they can get pulled apart into all of their little pieces. or if they enter the atmosphere of a planet to impact the surface, they might slowly get pulled apart as they enter the atmosphere and and end up being an array of little impacts instead of one big single impact.

[00:46:02]But what would happen if these impacts occur at sea?

[00:46:08]Will our oceans save us? Or will a giant tsunami wipe us out?

[00:46:18]Our hunt for the Milky Way's next supernova has identified some potential suspects.

[00:46:25]Very massive, lonely stars and stars with smaller sidekicks.

[00:46:33]In 2018, astronomers found a system called APE, 8,000 light-years away with two very massive stars.

[00:46:43]Each one about as massive as Beetlejuice.

[00:46:48]These are giant stars nearing the end of their lives with massive outer layers of gas that continually contract and heat up again and again.

[00:47:03]They become really huge and bloated and swollen and they're prone to huge outbursts.

[00:47:11]These unstable stars are called wolf raya stars.

[00:47:19]They're very rare and so hot and bright they emit more radiation than a million sunlike stars. This intense energy is blasting their outer layers off into space.

[00:47:33]>> Mass loss has been occurring from the star. So much so that you've actually lost all the hydrogen that was uh wasn't burned into helium. So now you have a star that's made uh entirely of helium and heavier elements.

[00:47:48]>> With no hydrogen left, these massive stars are running low on usable fuel.

[00:47:55]They're like ticking time bombs. Made even more dangerous because they're spinning so fast.

[00:48:04]>> It's spinning so quickly, it's on the verge of ripping itself apart.

[00:48:08]>> And this means that when this thing blows, it's going to blow hard.

[00:48:14]>> When a star goes supernova, its core collapses.

[00:48:18]The smaller it gets, the faster it spins.

[00:48:22]Some cores collapse into fast spinning neutron stars. Heavier ones like APE collapse into even denser and more mysterious objects, black holes.

[00:48:38]The immense gravity within APE's collapsing core will drag back some of the gas and dust into a spinning disc.

[00:48:48]As the material falls onto the core, it compresses and it speeds up.

[00:48:55]>> The dying star spins faster and faster as it collapses.

[00:49:01]And this incredible rotation drives the creation of massive magnetic fields that are capable of funneling material around and up and out in the form of huge beams of radiation.

[00:49:18]So the energy from the supernova collapse instead of being emitted spherically in every direction comes at us in a tightly focused beam like a laser from the Death Star. It is pointed in one direction.

[00:49:36]>> This is a gamma ray burst.

[00:49:40]>> It is the single scariest thing the universe has to offer. This is an explosion. so powerful that in a few seconds or minutes it can release as much energy as the sun will over its entire lifetime.

[00:49:56]>> You do not want to get caught in a gammaray burst. Let's just put it that way.

[00:50:07]The impact of a nearby gammaray burst on our home planet is almost too terrible to think about.

[00:50:14]It would be a very bad day for Earth.

[00:50:20]>> Earth's atmosphere could be partly blown away and there could be chemical reactions in the atmosphere that would form all kinds of noxious products.

[00:50:31]>> A gammaray burst from APE might last only 10 seconds, but its impact would last for decades.

[00:50:38]The generation of nitrogen oxide from a gammaray burst would be disastrous. In the upper atmosphere, it would eat away at our ozone layer. In the lower atmosphere, it would come out as acid rain. And the acid rain would destroy our crops.

[00:50:58]>> Nitrogen dioxide also filters out sunlight, turning the skies dark and cooling the Earth enough to trigger a new ice age. Any life on the land in the shallow parts of the sea or that live near the sea surface would be done.

[00:51:17]>> In fact, it would ultimately result in extinction.

[00:51:25]>> Blasted by ultraviolet radiation from our sun, freezing cold and hungry, humanity's future would be bleak.

[00:51:38]So, we really need to know when APE goes supernova and produces its deadly beam of gamma rays, are we in its line of fire?

[00:51:50]>> The good news is that we are probably not right in the direct firing line of APA.

[00:51:56]>> The axis of rotation of the APB system is pointed 30° away from us. So, if it does blow, it's likely that the jets are going to miss us.

[00:52:08]>> Makes me feel better that uh this gamray burst isn't pointing at us. But, of course, there are many other cosmic catastrophes potentially waiting to get us.

[00:52:18]>> APE is on the edge of an enormous explosion.

[00:52:22]Its huge gravity and incredible spin should produce a spectacular supernova.

[00:52:31]But what if some stars are too big to blow? Oh,