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00:00Across the universe, there are stellar systems totally different to our own, containing two
00:09stars instead of one.
00:12Our sun isn't so typical after all.
00:16Even the most fantastical imaginings of sci-fi writers, it doesn't even come close to what
00:21nature can produce.
00:24Binaries are binary stars, and they create some of the most lethal places in the universe.
00:33Any planet that's close by is going to get cooked.
00:38But some binaries may have a hidden, unexpected trick.
00:43One that could transform our search for alien worlds.
00:47When it comes to the occurrence of life on a planet, it may very well be that having
00:52two stars could be a lot better than having one.
00:56Imagine living in the light of two suns.
01:00Are we missing out?
01:02Could two stars actually be better than one?
01:22Staring up at our sky, you'll see the same ever-present, solitary sun.
01:29Rising and setting, day after day.
01:36But throughout the galaxy, alien civilizations could be enjoying twin sunrises and twin sunsets.
01:47Because they orbit two stars instead of one.
01:52Half the star systems in our galaxy are binary stars.
01:55It appears to be a common root of stellar formation and evolution.
02:00So we can't just focus on the single star systems and think we have a complete picture.
02:08The complete picture may include planets orbiting binary stars.
02:13Worlds completely alien to us.
02:17And worlds ingrained in sci-fi fantasies that have inspired for decades.
02:22If there is one single event that I can most link to why I became a scientist, it was going
02:27to see the original Star Wars movie, Episode IV, when I was seven years old.
02:31And I can remember that scene of Luke Skywalker standing out on the deserts of Tatooine and
02:36there's a double sunset.
02:38The music swells up and I can remember my seven-year-old heart kind of leaping out of
02:42my chest.
02:43That's the moment when I realized I wanted to be an astronomer.
02:49Could two stars be even better than one?
02:52Living on a planet that orbits a binary system could be really exciting.
02:56Imagine seeing two stars in the sky every day.
02:59That's pretty cool.
03:00But you know what?
03:02Sometimes it can get too exciting.
03:08Some binary systems are not places for sci-fi adventures.
03:12They're horror stories.
03:15In some cases, the interactions between binary stars get deadly.
03:19The stars can actually turn on each other.
03:22Binary stars are kind of like siblings.
03:23They're born together and they grow up together.
03:26But sometimes one of those siblings can be evil.
03:32This evil sibling is a pulsar.
03:36It started life billions of years earlier as the big brother in a binary.
03:43But something then transforms it into a monster.
03:51When a large star dies, it will end its life as a supernova with a crazy big explosion.
03:56And the pulsar is what's left behind.
04:01Its death triggers one of the biggest bangs in the universe.
04:11In the midst of the explosion, the star's core collapses, crushing material down into
04:18a hyper-dense ball.
04:22Rapid rotation and intense magnetic fields trigger twin beams of deadly radiation.
04:29And a pulsar comes to life.
04:33The pulsar has to be one of the most amazing monsters that the universe has ever thought
04:37of.
04:38They're only about ten miles across, and yet they contain the mass of at least the
04:43sun or even sometimes twice the sun.
04:48The pulsar's sibling is lucky to survive the chaos of the nearby supernova.
04:56But it now orbits a brother from hell in a cosmic wasteland.
05:02Orbiting a pulsar would be a pretty rough experience for any object in its vicinity.
05:07Pulsars are spitting out tremendous amounts of lethal radiation from their poles.
05:11It wouldn't be good to live on a planetary system near a pulsar because you are going
05:18to be pointed toward a laser of planetary death.
05:24But these death rays can't last forever.
05:29Within a few million years, the pulsar spins itself to death.
05:35With its evil sibling dead, can the other star finally live in peace?
05:42Stars, as I tell students, are a lot like people.
05:47As they age, they tend to expand a bit.
05:51For a single star, it can expand and be as big as it likes.
05:56But in a binary, there's a problem.
06:01As the star expands, the outer layers move farther away from the center.
06:07The further away they become, the less gravitationally attracted they are to the star.
06:13This reaches a limit called the Roche Lobe.
06:17The Roche Lobe is important basically because it tells you the biggest possible size that
06:24a star can be in a binary star system without impinging on the gravitational influence of
06:32the other star.
06:36The Roche Lobe is similar to a dam holding in a reservoir of water.
06:42But if the reservoir gets too full, the water overflows into the spillway.
06:47This is what happens to the sibling star.
06:53The star expands.
06:55It eventually reaches the level where it's going into the spillway.
06:59It's going into the gravitational domain of the pulsar.
07:04Now this is where the story gets really interesting.
07:06So you've got your companion star that's swelled up into a red giant.
07:10Some of that red giant material now can get incorporated back into the pulsar and spin
07:15it up into something called a millisecond pulsar.
07:20The bloated red giant can't hold on to its outer layers, and the pulsar begins to feed.
07:29Matter streams into it, transferring momentum to the pulsar, spinning it faster and faster
07:38until it rotates hundreds of times a second.
07:42The beams then reignite, and once more, our pulsar is back from the dead.
07:49They're dying and resurrecting over and over and over again.
07:52It's like a zombie you just can't kill.
07:58The red giant extends the life of its zombie brother by billions of years.
08:07We know of hundreds of millisecond pulsars scattered across the cosmos.
08:12A terrifying thought.
08:20But what's even scarier is that some of them are alone.
08:25What's happened to their sibling?
08:29Binary stars are ultimately responsible for the existence of millisecond pulsars.
08:33They only exist because they've sucked life out of their companion stars.
08:40The millisecond pulsars that we see that are all alone may have just gotten rid of the
08:44body.
08:47This is PSR J1311-3430, a rare breed of millisecond pulsar known as a black widow.
09:01Similar to its spider namesake, it's deadly.
09:05One of the most massive, fastest-spinning pulsars in the universe, emitting 100 times
09:11more radiation than a standard pulsar.
09:16A black widow pulsar is right on the edge of physics.
09:19Any larger and it would be a black hole.
09:21The intense radiation is amazing.
09:24It's hard to fathom that these things exist.
09:27Generally, the rule is the following with the universe, which is big and old.
09:31If it can happen, it does happen.
09:34And every time we discover a new exotic object, it allows us to test the laws of physics in
09:38a way we couldn't before, which is why, as a physicist who's interested in fundamental
09:42physics, I so often turn to the universe, because the universe is a wonderful laboratory.
09:47It can create things we can never create here on Earth.
09:52The black widow pulsar is the stuff of nightmares.
09:57Its radiation heats the companion star to nearly 12,000 degrees Celsius, more than twice
10:03as hot as the surface of our sun.
10:10It's nothing less than stellar annihilation.
10:16Pulsars are already dramatic, energetic events.
10:20Now you're adding in, hey, let's destroy a star.
10:23Black widow spiders famously eat their mates.
10:26And that's exactly what a black widow pulsar does.
10:29It actually uses the material from its companion star to spin itself up, and then it obliterates
10:34it completely.
10:36The companion star vanishes, destroyed by its zombie sibling.
10:45It's the ultimate cosmic ingratitude.
10:47Here you have the companion star that's brought the pulsar back to life after it's died twice.
10:52And now its entire body is eviscerated by the radiation of the pulsar, without a speck
10:57of dust to suggest it was ever there.
11:02These black widow pulsars are like the assassins of the galaxy.
11:06Not only do they destroy the star, they get rid of the evidence.
11:12When pulsars are involved, two stars are much, much worse than one.
11:20But could the opposite also be true?
11:25Could two stars create a habitable oasis on alien worlds?
11:49Binary stars offer an exciting possibility.
11:57Alien exoplanets that orbit two stars instead of one.
12:03These binary stars are everywhere.
12:06So the universe could actually be something like what we see in sci-fi movies.
12:13The Tatooine sky could be a real thing.
12:16There could be a planet with life and civilization, and in the sky there could be two suns.
12:24What would it be like to live on these worlds?
12:28Could two stars be even better for life?
12:33Our home planet orbits a solitary sun in a safe region where life could evolve.
12:41Today we're familiar with a very stable, well-behaved star, our own sun.
12:46And of course we know there's some solar weather, sometimes it throws out high-energy particles
12:50that create the northern and southern lights, but it's a very reliable star.
12:54It wasn't always that way.
12:56When the sun was much younger, it was more active, it was more violent.
13:04Our young sun rotated over ten times faster than it does today, causing its magnetic field,
13:11to twist and tangle, sending out huge solar flares.
13:20Solar flares can be very bad for the habitability of a planet, particularly if you're very close
13:23to the star, and the reason is because solar flares essentially represent high-energy radiation,
13:28for example high-energy protons.
13:30They smash into the atmosphere and they can strip away gas off the atmosphere.
13:37Picture the early solar system.
13:41Flares and solar storms attacked the atmospheres of the rocky planets.
13:47Deadly charged particles ripped them away, molecule by molecule.
13:54And without an atmosphere, liquid water couldn't survive.
13:59And no liquid water means no life.
14:04In the very early stages, our solar system was an awful place.
14:08The sun was young and highly irregular and emitting lots of energy in our region.
14:15It took a long time, probably 500 million years or so, before the solar system calmed
14:20down enough to imagine that anything like life could evolve here on Earth.
14:28This is a galaxy-wide problem for planets orbiting one star.
14:34Take Proxima Centauri, the closest star to our sun.
14:39It's a red dwarf, the most common type of star in the Milky Way.
14:46It even has its own planet, named Proxima b.
14:52But Proxima Centauri has not treated its planet gently.
14:59If there is any water on Proxima b, then it would be extremely lucky.
15:08Proxima Centauri would have caused huge amounts of energy to come out and it would effectively
15:12strip away Proxima b of any kind of atmosphere or surface water, thereby removing any chance
15:18of there being a habitable world.
15:21The only hope we have left for Proxima b is a strong magnetic field.
15:25This would surround and protect the planet from the onslaught of violent energy that
15:31comes out of Proxima Centauri.
15:33And that way there could still be an ocean, there could be an oxygen-rich atmosphere and
15:37perhaps a habitable environment, somewhere where life could have started.
15:41But right now, for Proxima b, the odds are stacked against it.
15:50Earth's strong magnetic field protects us from the sun's worst outbursts, allowing
15:55liquid water to survive.
16:00But other planets, such as Mars and Mercury, haven't been so fortunate.
16:08Solar storms blasted their young atmospheres until they became thin and weak, snuffing
16:14out any chance of life.
16:22But could binary systems actually make things easier, where planets orbit around two stars
16:28instead of one?
16:32Young stars can be very violent and chaotic, but in the system where there are two stars,
16:37the interaction of those stars can slow down their rotation and that means that that violence
16:43can be slowed down.
16:45These solar storms can be tempered, so they're not as violent, they're not as frequent.
16:50And if any young planet is formed with an atmosphere, it can keep it.
16:56So when it comes to the occurrence of life on a planet, it may very well be that having
17:01two stars could be a lot better than having one.
17:07Gravitational interactions can slow down the spin of two close, sun-like stars, giving
17:13life the chance to develop.
17:17And not just on one world, on many planets throughout the system.
17:24With two stars in the middle of the solar system, you have twice the amount of heat,
17:27twice the amount of light.
17:28And that extends the habitable zone farther out into the solar system.
17:35For planetary scientist Janie Radabaugh, exploring systems such as these would be a dream come
17:42true.
17:43I mean, to me, it is so thrilling that worlds like this could exist and that they might
17:49even harbour life.
17:50I mean, there could be a sci-fi desert planet like this one with twin suns, my personal
17:56favourite and one that I can't wait to visit.
18:00Or if we wanted, we could just hop over to another habitable planet and find something
18:04completely different.
18:08Travelers could explore a variety of sci-fi landscapes.
18:17Perhaps alien civilisations are already out there, living on these habitable worlds.
18:28Two suns could create better star systems than one, but they could also make things
18:34chaotic, shooting entire worlds into space at hyperspeed.
18:59What would life be like on a planet in a binary system?
19:05Would it be better?
19:08Or is planet Earth really as good as it gets?
19:12If you're looking for an abode for life in the galaxy, we tend to look for a rather cosy
19:17existence out there, but it's possible that stars can take you on a bit of a wild ride
19:21sometimes.
19:25Over the past decade, we've observed mysterious objects hurtling through the galaxy.
19:33Scientists call them hypervelocity stars.
19:37When we say hypervelocity stars, we're talking some hypervelocities.
19:43They've been observed moving up to 620 miles per second.
19:47You're talking about something the size of a star, the sun, an octillion tonnes of mass
19:52or something like that, getting flung away way faster than a rifle bullet.
20:00These hypervelocity stars start off in a binary system, but something tears them apart.
20:08Something big.
20:11In order to create a hypervelocity star, you need a very intense source of gravitational
20:15power.
20:16Well, the most intense source we know of is the black hole at the centre of the galaxy.
20:28This black hole is Sagittarius A star.
20:36It is supermassive, four million times the mass of our sun.
20:44Two stars stray a little too close, and the enormous gravity of the black hole pulls at
20:50them.
20:53The star closest feels a much stronger tug, and this binary system is then ripped apart.
21:02It's a little bit like the Olympic hammer throw, where the hammer is one star in the
21:06binary system and the Olympian is the other star, with the cord connecting the hammer
21:12being the gravitational tie between the binary stars.
21:15If you cut that cord, the other star can go flying off at very, very high speed.
21:24Once the cord is cut, the binary stars separate forever.
21:30One is trapped in the gravitational grip of the black hole.
21:36The other is flung out of the galaxy, becoming a literal shooting star.
21:42However, the star may not be alone.
21:47If a planet is gravitationally bound to a star and that star gets ejected from the system,
21:54if conditions are right, that planet can hitch a ride with that star.
21:59Where the star goes, the planet goes.
22:06If you're on a planet around a hypervelocity star, you would be the envy of poets and scientists
22:11everywhere because you would have the most breathtaking view imaginable.
22:15You would start at the very centre of the galaxy and have this beautiful view of the
22:19supermassive black hole.
22:25Generation after generation on this hypervelocity planet would be treated to thrilling new views
22:31of the galaxy.
22:37By the time you're done, as you're ejected, you would see the entire Milky Way galaxy,
22:43everything, and it would recede away from you as you moved off into space to who knows
22:49where.
22:55Hypervelocity planets just demonstrate that the universe is much stranger than fiction.
23:02As we learn more about stars and stellar systems, even the most fantastical imaginings of sci-fi
23:08writers, it doesn't even come close to what nature can produce.
23:17This hypervelocity star, along with its planet, go on the journey of a lifetime.
23:24But what about the stranded companion star, stuck in the centre of the galaxy next to
23:30a supermassive black hole?
23:34It too could have a planet orbiting it, but it's a world living on borrowed time.
23:40If there's a planet orbiting the star that gets left behind by the hypervelocity star,
23:45so the planet is now orbiting the star that's orbiting the black hole, that's not probably
23:50going to last very long.
23:52Typically, the little guy gets shot away.
23:59So it's entirely possible that we have hypervelocity rogue planets, planets without a star, that
24:06are shooting out of the galaxy at high speed as well.
24:11But travelling on this planet is not a trip you'd want to take, because this world is
24:18destined to wander through the emptiness of space forever, and alone.
24:26The problem with a planet is that it's no longer bound to a star, so the outer surface
24:30would most likely freeze.
24:35Binary stars create weird environments for planets.
24:39You could get an exhilarating view of the galaxy, or you could freeze on an icy wasteland.
24:52So are two stars better than one?
24:56There's one thing of which there is no doubt.
25:00Binary systems are certainly dramatic.
25:03And there's even one that has two stars so close, they're touching.
25:09KIC 983227 is a very interesting binary system.
25:14It's what we call a contact binary.
25:17So this means that the two stars are basically in contact, but they're separate stars.
25:22They share a common atmosphere, or envelope.
25:26One's about a third the mass of the sun, one about 1.4 times the mass of the sun.
25:31And they're rotating around each other every 11 hours.
25:36In 2017, scientists from Calvin College revealed an exciting discovery.
25:43These binary stars are moving even closer together.
25:49And then after further calculations, they made a bold prediction.
25:54So this star is different from all other contact binary stars we've studied, because this one
26:00we believe, in the next five years, is going to merge, spiral in together, and explode.
26:09But it's a star close enough to us, only 1,800 light years away, that when it explodes, it'd
26:16be bright enough to see with your naked eye.
26:19Two stars crashing together.
26:23An event known as a red nova.
26:26If this is true, if we really see it, it would be fabulous, because not only would it validate
26:31this amazing prediction, but we have something new to look at in the night sky.
26:35If this comes through, this will just be the event of my lifetime.
26:43We don't get to predict too many things in astronomy, except, you know, a billion years
26:48from now, this thing will happen.
26:51So you have to appreciate what this thing is.
26:55These stars are probably billions of years old.
26:58We're just so lucky to be able to see this right at the end, where we just have a few
27:03years left.
27:04A few years out of a billion year lifespan.
27:12It's an amazing cosmic coincidence.
27:16Yet even more remarkable is that before these stars came into close contact, they may have
27:22had a neighbor, a distant third star, that set all this in motion.
27:30Whenever you have three objects, the gravitational dynamics becomes incredibly complicated.
27:36The third star pulls on the binary as the two orbit each other, stretching them out
27:42basically into an elongated orbit.
27:45The two stars resist that, trying to circularize their orbit again.
27:50That back and forth interaction pushes the third star further away, pulls the two stars
27:56closer.
27:59The stars have been pushed into close contact, but it doesn't end there.
28:08Matter will stream off the smaller star until it's too gravitationally weak to hold its
28:13position.
28:16This will drive their orbits even tighter together, moving them faster and faster.
28:24Finally, the smaller star will plunge into the larger, tearing through it, and blasting
28:33hundreds of trillions of tons of debris in every direction.
28:40This will be an enormous amount of energy.
28:42The explosion at its peak will be 10,000 times brighter than the star is today.
28:49This collision is not just an act of annihilation, but one of creation.
28:56The cores of the two stars will collide and become one, creating a super hot blue ball
29:01of gas, a newborn star.
29:07Just think about how cool that is.
29:09In the constellation Cygnus, in about five years' time, a new star is going to turn on,
29:14created from two older stars, an entirely new way of seeing a star being born.
29:22Around this star, searing hot gas will expand outwards, turning red as it cools, becoming
29:31the red nova.
29:36The explosion will create a brand new light in our night sky, as bright as the North Star.
29:47It's just phenomenal that we get this opportunity.
29:50This is what every astronomer wants to do.
29:54Fortunately, we are at a safe distance to witness this cataclysmic collision.
30:03But would we feel the same way if we were on a planet orbiting this binary system?
30:08This is a very, very energetic event.
30:11Could life survive such an event?
30:14I wouldn't want to be there as the test guinea pig.
30:21All this energy comes pouring in, and your atmosphere is likely to be stripped away.
30:26If there are oceans on this world, they are likely to be vaporized, and there may be very
30:32little left other than rock.
30:35A nova is nothing you want to fool around with.
30:37Any planet that's close by is going to get cooked.
30:40It's going to get sandblasted, and then, you know, there it is.
30:44If that's the kind of place you want to be, hey, more power to you, but I like Earth.
30:54It seems that Earth is fortunate to have just a single star.
30:58No collisions, no explosions, no drama.
31:06For two stars to be better than one, we need to find rocky planets in a binary system.
31:14But so far, we haven't, raising the question, can they really exist at all?
31:28The Kepler Space Telescope has completely changed our search for alien worlds, discovering
31:47thousands of exoplanets orbiting single stars.
31:54When I began my career in astronomy, the thought of planets around other stars was kind of
31:58a pipe dream.
31:59We didn't know if they existed.
32:01And now we're living in an era where we're finding them by the thousands.
32:05We know we live in a populated galaxy.
32:08There are planets galore out there.
32:10It's been a paradigm-shifting couple of years.
32:15The more we discover in the dark ether of space, the better our understanding of the
32:21universe.
32:22When we first started this game of discovering exoplanets, it really was more just a hunting
32:27stage.
32:28But now I think we've evolved into the gathering stage, where we're finding many, many exoplanets
32:32and we're able to learn about the mechanisms which ultimately are forming these worlds
32:37in alien systems.
32:41Telescopes are not just looking at the single stars.
32:44They're also searching binary systems.
32:47And there's one thing scientists most want to find.
32:53It would be an incredible discovery if we found a truly Earth-like planet around these
32:56binary star systems.
32:57In many ways, that's kind of the holy grail of what we're doing when we look for planets
33:00around binary stars.
33:04But finding rocky planets in binary systems is proving difficult.
33:12We have found planets orbiting binary star systems, and that's a big leap forward in
33:16our understanding of how the universe works.
33:19Unfortunately, those planets have all been gas giants, and they're not really good for
33:23forming life.
33:27For alien civilizations to exist around two suns, they need to be on solid ground.
33:34So far, the hunt for this holy grail has been fruitless.
33:39We always have to consider that maybe rocky planets around binary stars just don't exist
33:44for some reason that we currently don't know.
33:47And that would mean there would be no Tatooine.
33:53But paired stars make it impossible for a rocky planet to form.
33:59If you're a planet trying to form around a binary system, the gravity in the middle is
34:03always changing.
34:04Instead of a single star, you have two stars orbiting each other.
34:10Two infant stars start a gravitational tug-of-war.
34:17The material between them is pulled in different directions, making it harder for bits of rock
34:22and dust to stick together.
34:26The system seems too chaotic for rocky planets to form.
34:31The complex gravitational interactions at play destabilize a lot of potential orbits.
34:38There aren't a lot of opportunities for a young planet that might want to form to find
34:44a stable, long-term home that lasts for billions of years around that binary system.
34:50It's relatively easy to get ejected or consumed by the stars themselves.
34:59So why can't rocky planets survive when gas giants can?
35:05As any good estate agent will tell you, it's all about location, location, location.
35:12We think that rocky planets tend to form close in around stars where it's nice and warm,
35:17but further out where it's colder, you have the gas giant planets forming.
35:20So if you have a binary star system, it's like a gravitational tornado whipping out
35:25all of that rocky material, so that you're only left with the cold stuff which can form
35:29gas giants further out.
35:32If a two-star system were a city, the gas giants are on the outskirts, a nice, peaceful
35:40spot, far away from the competing gravity of the two stars.
35:47Perhaps one-star systems are better than two.
35:51Gas giants aren't conducive for life, and those are the planets we're finding in these
35:55binary systems.
35:59The very reason that we're here could be down to the fact that we have one star rather than
36:02two.
36:06But in 2017, a discovery around 2,000 light-years away gave us new hope.
36:15So as we discover new things in the universe, we tend to give them catalog names, which
36:20can be very boring and very difficult to keep track of, but SDSS 1557 is worth remembering.
36:31We've seen a binary system that is a white dwarf, which is the core of a star like the
36:35sun after it's gotten very old, blown off its outer layers, that's orbited by a brown
36:40dwarf, an object which is sort of on the border between a planet and a star.
36:46What's most exciting about the SDSS 1557 system is that we found rocky debris.
36:55We see the basic materials, the basic ingredients are there for forming planets.
37:00This is a really exciting discovery because we've seen the remnants of asteroids and rocks
37:04orbiting about this ancient binary system, systems that we thought could have never had
37:10surviving rocky-type things around it before.
37:15This binary system is billions of years old.
37:19And through all that time, the rocky material hasn't been obliterated.
37:24It has survived.
37:29This is a huge stepping stone to finding a rocky planet with two suns.
37:36This system provides evidence that there was rocky material close in around a binary
37:40star system.
37:41So it's a signpost that rocky planet formation can occur around binary star systems.
37:47The odds might be longer, but it's still possible.
37:53Could there even still be a planet in this system?
37:57There may still be planetary objects around SDSS 1557.
38:01We just haven't seen them yet, but they may still be there.
38:11The hunt is still ongoing.
38:15A rocky planet orbiting two stars could really exist.
38:21So for those of us hoping for that Tatooine out there, that planet with a double sunset,
38:26these debris fields actually give us hope.
38:28Only the conditions, at least, are right for the formation of rocky planets around
38:32binary stars.
38:34I think it's out there.
38:35I think finding it is more a question of when than if.
38:39As an astronomer, this is a fantastic time to be alive at the cusp of discovery.
38:44As a science fiction fan, this is a fantastic time to be alive because the stuff I read
38:49as a kid is coming true.
38:56Perhaps the biggest sci-fi fantasy is much closer to home, because new research is suggesting
39:04something stunning.
39:07Our own sun could have a twin.
39:12For the first time now, astronomers are able to peer inside the clouds that form stars.
39:18And the amazing thing is that the evidence is suggesting that every single sun-like star
39:23forms as part of a binary pair.
39:27The scientists studied the Perseus Molecular Cloud, a stellar nursery around 750 lychees
39:34from us that's packed with stars just like our sun.
39:41Many of them are in wide binary systems travelling in huge orbits around each other that span
39:46centuries or more.
39:51And all of these binaries are young, less than 500,000 years old.
39:58The only way to explain these young systems is that they form this way.
40:05Not alone, but in a pair.
40:12Just based on statistics and our understanding of what's going on inside these star-forming
40:16clouds, it is highly likely that the sun formed with a twin.
40:24Perhaps four and a half billion years ago, our sun burst into life with a sibling.
40:33Could this twin still be out there now, in a distant orbit that we haven't seen?
40:40There was an idea that the sun could have a companion, which was nicknamed Nemesis.
40:45And this thing would have orbited way far out, way past Neptune in the solar system.
40:52Scientists searched for this Nemesis star, but they found nothing.
40:59We've looked, we've had telescopic surveys of the sky, including infrared surveys where
41:04these types of objects would be very bright.
41:07And we have swept the entire sky multiple times, and we've seen nothing.
41:17What happened to our sun's sibling is a mystery.
41:22How do we end up with one star as opposed to a binary?
41:26We really don't quite understand.
41:30Who knows?
41:31It may even have left our system long ago.
41:36Over time, some of these binary stars get closer together and stay together, and others
41:40get ripped apart and lose each other entirely.
41:43It's very possible that our sun, at some point, had a twin that got ejected.
41:51We don't know exactly when our sister star was torn away.
41:55It could be clear on the other side of the galaxy from us by now.
42:00Not after everything we've seen in binary systems.
42:05We may be much better off without it.
42:09I'm pretty happy with having just one sun, so I'm fine to live in this solar system.
42:15A binary sunset would be more beautiful, but only more beautiful if you're alive.
42:22Yet binary stars don't just bring death and destruction.
42:27They could also create systems with a series of habitable worlds.
42:34There's so much we don't know about our own environment and how it compares to other places
42:37in the universe.
42:39It seems like we're in a very lucky place.
42:41The sun is very stable, it's a single star, we're in a nice orbit around it.
42:46But maybe there are places out there that are even better.
42:48We just didn't even know to ask.
42:52It certainly is possible that two stars are better for life than one.
42:57However, until we find these alien worlds, it remains an open question.
43:07It's hard to say whether we're lucky or unlucky to be on a planet orbiting a single star.
43:12It's probably a little boring here compared to what it would seem like in these binary
43:17star systems.
43:21You know, from a romantic visual perspective, I kind of wish we did live in a binary star
43:26system.
43:27Can you imagine somebody living on a circumbinary planet and finding an Earth-like planet orbiting
43:33a solitary star?
43:34Would they think, oh, how interesting that would be?
43:37Can you imagine having one sunset?
43:39What would that look like?
43:40I can imagine them asking themselves the questions we ask ourselves.
43:45So it's just, it's a matter of perspective, you know?
43:47Grass is always greener on the other side of the binary system.