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As a SciShow viewer, you can keep building your STEM skills with a 30 day free trial and 20% off an annual premium subscription  at Brilliant.org/SciShow. It might not seem like it, but our solar system is … weird!

For one thing, unlike our solo Sun, most stars out there have at least one partner. Imagine what the sky would look like if we threw another sun into the mix. What the orbits of all the planets would have to be to make it all work out.

Now imagine if Earth had three suns. Or four! Some planetary systems  actually work like that.

And to make it happen, the orbits can get a little brain-bendy. Especially for any planets,  which being a lot less massive, are a lot more beholden to their stars’ movement. So in this SciShow list show, we’re exploring some of those  wacky multi-star systems, how planets can exist inside of them, and how we even know about  them in the first place. [Intro] Now organizationally speaking, our one-star system is not too far  off from some two-star systems.

In that setup, a planet like Earth  still orbits around a single point. Only now, that point isn’t where one star exists, but rather where two stars… orbit each other. Those two stars form what’s known as a binary.

And they’re just swinging around each other like two besties holding hands and  spinning in circles in a field of daisies… if those besties also had really stretchy arms so they weren’t always the same distance apart. A planet can circle around that binary in what’s called a circumbinary orbit. That’s how the BEBOP-1 system works.

Thanks to two separate discoveries,  using three separate telescopes, astronomers know that BEBOP-1 has two gas giant planets  that both orbit two stars in roughly circular orbits. That’s a lot of bodies swinging around each other. But gravity allows it because proportionally, the stars are much closer to each other than either of them is to a planet.

While the stars orbit each  other once every 14.6 days, the inner planet orbits the  binary once every 95.2 days. So if you were in a levitating  city on one of those gassy planets, it would look like Star Wars’s Tatooine! There would be two suns in your sky that stay relatively close to each other.

Aside from adding credibility to Star Wars’s stunning sunsets, BEBOP-1 is an exciting system for researchers because it’s bright enough to be a  new target for the Webb telescope. It could teach us about the atmospheres  of circumbinary planets and, as the researchers say, “provide a new hope” to unravel their mysteries. Amazingly, that was not our pun; that was the researcher's pun.

So that’s an example of a two-star system. And adding just one more star …going from a binary to a trinary… can’t change too much, right? Well, it turns out that that third star makes things so much more complicated.

Now one of them could get kicked out, or the entire system could fall apart. And that’s not even getting to the planet issue. Sure, maybe physics would allow a trinary version  of the BEBOP-1 system, with a planet or two orbiting super far away from the complicated dance three stars have to do with one another.

But there are cooler arrangements that exist, too. For example, instead of orbiting  all three stars at once, it’s mathematically possible for a  planet to orbit just one of the stars, which is then in its own long  distance relationship with a binary. And guess what?

The trinary next door  actually has this arrangement! Collectively, the three stars that make  up the Alpha Centauri system are about 40 trillion kilometers from our Sun. Which is simultaneously super far away, and still three times closer than  any other Sun-like star out there.

The two central stars, known as Alpha Centauri A and Alpha Centauri B are very similar to ours in terms of appearance. But the planets we’ve found are orbiting the third star in the trinary, a red dwarf called Proxima Centauri. Which is only about 14% the size of our sun and 0.15% as luminous.

So it’s a little guy, but it’s got enough going for  it to have at least two planets… one a little more massive than Earth, and the other one that’s closer in mass to Mars. If you were standing on either of these planets, a daytime sky would be a little more red and a little less bright than you’re used to. Because even though you're  in orbit of such a dim star, you’re way closer than the Earth is to the Sun.

And unfortunately, Alpha Centauri A and B are so far away they’d just be two distant  white dots among a sea of stars. Which is a bit disappointing from  a space tourist’s perspective, but sometimes you’ve gotta make sacrifices to fit three whole stars  into one planetary system. Now there are plenty of binary and trinary systems out there, but systems with four stars are harder to find.

So you might think that only  the most experienced researchers with dozens of publications under their belt could identify a planet in one. But the first four-star planetary system  was discovered by a group of amateurs. Like, Now before 2012, researchers knew that there was a stellar binary in the system with the melodious  catalog name KIC 4862625.

But that system was about  to get totally reclassified thanks to citizen scientists who may not have had any background  in physics or space science. They were volunteers who spent their free time looking through data collected by  NASA’s Kepler and TESS missions, just because it’s cool. It’s a project called “Planet Hunters”, where anyone can sign up to  comb through this public data in the hopes of finding new exoplanets.

And in this case those hopes turned into results. Each volunteer is randomly assigned a small section of the missions’  datasets from over 300,000 stars. And their job is to draw a box wherever they see evidence of a little dip in a star’s brightness.

Because sometimes, what they’re seeing in that dip is a  planet passing in front of its star, blocking some of the light from reaching us. And sure, you could do some of this work with a computer program. But if there’s more than  one star in close proximity, like when there’s a binary, the planet’s signal can be hidden among the dips caused by the two stars blocking  some of each other’s light.

And where algorithms might fail to spot that detail, human eyes can catch something worth following up on. Spoiler alert, that’s what citizen science  did for KIC 48 et cetera …all those numbers But once this particular system caught their eyes, these amateur astronomers looked deeper and found a second binary of  stars had been there all along. This was a four-star system, making it the first four-star system with a planet in it as far as NASA knows.

So there’s a binary of stars circling each other, with a planet orbiting both of them, and  another stellar binary going around all of that. If you were looking at the sky from this quadruple star planet, you’d probably see two Suns and one very bright star which is actually two stars  smushed right up together. It’s like how from Earth, you can look up at the Big Dipper and totally miss that some of the stars are actually multi-star systems.

So hats off to citizen scientists for showing us cool systems like this one! And yes, astrophysicists had to then officially confirmed the findings. But this huge discovery  could have been made by you, or your neighbor, or the person operating the  camera for this SciShow video!

And since that discovery, researchers have started to realize that four-star  systems are more common than they used to think. Could there be planets in 5+ star systems? But a planet in a five-or-more-star system?

That’s still hypothetical …at least as of filming. Astronomers have found systems with five, six, and maybe even seven stars. And odds are there are more out there.

So we know that stars can group together in these big batches. But at this point in time, we haven’t found any evidence that a planet can coexist with all of that. I mean, it’s hard enough to find all of the stars in a crowded system.

For example, in the five-star system whose name I’m not even  going to try to say out loud, researchers were totally missing  the fifth star for over a year. They originally reported two binaries in a double eclipsing four-star system. The dimmer binary was identified first, because they thought the brighter one was just a twinkle glinting  off one of the other stars.

But something about this system  made them want to look deeper. Even after they thought they’d determined that it was a four-star system, they kept an eye on it because the two stars in one of  the binary pairs orbited each other faster than in any known four-star system. So when another research team claimed to find a fifth star traveling at the  same velocity as the rest of them, the original team agreed that it’s probably a package deal.

Maybe one day astronomers will find out there’s a  planet in that package too. Or maybe they won’t. But while we’re shooting for the stars, why not talk about six-star systems that could theoretically be home to planets too?

One six-star system we’ve recently  discovered is called TYC 7037-89-1. It’s made up of three  binaries that are all similar in mass, size, and temperature. Two binaries orbit each other.

Then, those four do a big  dance with the third binary. Now, each of the binaries has a pretty short orbital  period of only a matter of days. They’re all tight pairs.

But the orbits of the binaries  around each other are much larger, giving them room to spin around each other as they move. They’re also far enough away that each binary can act like  just one source of gravity, making the physics a lot less messy. Ultimately, there might be other kinds of  six-star systems out there, like two sets of triplets.

But because the third star in each triple would have to orbit so much farther away, we’re more likely to find  six-star systems like

TYC: a triplet of binaries. Since these larger, more complicated systems are harder to find and stick  together in the first place, it might not be too surprising that we haven’t found any planets in them so far. But in space, sometimes you  just have to keep looking. Maybe a few years of searching will lead to new discoveries.

And we’re going to make them all from our solar system with just the one star. Which works perfectly well for us. One thing that all of these  solar systems have in common is that their stars are brilliant, just like this video’s sponsor!

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So you’ll come for the calculus of  motion and stay for electrostatics. To try it free for 30 days, you can visit Brilliant.org/SciShow or click the link in the description down below. That link also gives you 20% off an  annual premium Brilliant subscription.

Thanks for watching! [ OUTRO ]