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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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with thousands of interactive lessons in science,
computer science, and math.
Like their course on Vector Calculus!
This course gets into some concepts
that any planet hunters out there would find really valuable,
including calculating planetary orbits.
So you’ll come for the calculus of motion and stay for electrostatics.
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Thanks for watching!
[ OUTRO ]