I'm Mike Lemonick, and I'm really
interested in exoplanets, planets around
other stars.
I'm Lee Billings, and I too am very
interested in planets around other stars.
Yeah, well I wrote a book about exoplanets.
Really? That's nice because I did too
actually.
Ok fine. Anyway we're here to talk about
a really bizarre development in
exoplanet science. Some scientists have
discovered that it is likely that black
holes create planets and shoot them out
across the university at millions of miles per hour.
That's pretty crazy but it's
not the first time we've seen some
craziness with exoplanets.
The whole history of the field
is kind of filled with surprises.
Yeah so let's talk about how we used to think
planets formed: giant cloud of interstellar
gas and dust gets nudged by the gravity
of a star or something and it starts
to collapse and collapses and collapses
and spins faster and faster and the center bursts
into nuclear fire as a star.
And the rest forms this disc, and the dust
and the gas in the disc start to clump together-
here I'll show you - to form rocks
and those clump into boulders and the boulders
clump into mountains, and the mountains clump into
things like the size of the moon, maybe, or Mars.
And those smash together and eventually
they form into something like the Earth!
What about a planet like Jupiter?
It's pretty similar actually. So you know you
get - wow this stuff's tough - you get like
a core together maybe about Earth's size
or a little bigger.
This is rock also. Yeah this is rock
as well. This is rock and solid stuff.
You get the core together and then what happens
is out in the outer parts of the disk
you just get - oh wow this is really hard gas -
you get some gassy material that kinda
gloms onto it...yeah gravitational
field just sucks it all together and you
get a bigger planet because there's more stuff.
This is called the Core Accretion Hypothesis-
the idea that we get these
rocky solid cores and discs and
close up to the star, where it's really hot, you mostly
have rocks and metals and things like
that that form the planets.
Whereas further out, you have ices and gases that
linger in the cold. So you end up with a
giant gassy planet like Jupiter with a
rocky core. That's right.
Or you have a rocky planet like Earth which is
actually suitable
for life. You know maybe we could have
viruses somewhere in the cloud tops of
Jupiter. Probably not, but maybe.
Let's not get crazy.
Okay. Except we learned in the early
nineties that it doesn't always work
that way.
That's right! So the very first planets
we found around other stars totally
upended this model. We had a pulsar
planets that were found. Pulsars are
remnants of normal stars. They're
neutron stars essentially that are left
over after a big supernova explosion
after a star dies. Right. And you know
when a star dies it blows up and sweeps
away all the stuff around it including
planets whether it's a big one or the
little one. But we found these small little
hunks of rock around these pulsars.
Somehow they recondensed and reformed
planets from the debris of the explosion.
Right, so pretty unexpected.
But then in 1995 we found a more normal planet
around a more normal star, right?
You'd think. You think, but it wasn't so normal.
It wasnt that normal because it was
one of these big guys and it was right
in like a few day orbit around its
around its star. So how the heck do you
get something like Jupiter that's only a
few days away from its star, when as far
as we know it only forms really far out?
Right. So people have theories about how
that might have happened, you know it forms
far out and then spirals in. Any way, big surprise
but we've learned to live with it.
About that same time, astronomers started
to realize there was maybe an entirely
different way to make a planet like
Jupiter. So instead of little pieces getting
bigger and bigger pieces getting bigger
and then finally it sucks in the gas,
the theory was that you could also form
something like Jupiter directly from
that cloud of gas and dust just clomped
together all at once. Right, much much faster.
And there are different ways that
this could affect how the planets look
but we really don't have a good
sense, really, of I think which one is
the prevailing model and chances are
they're probably truth somewhere inbetween.
Right so that actually brings us
to this new discovery that planets might
be able to be formed by black holes like
little spitballs that they shoot across
the universe.
So how could that possibly happen?
Well the idea is that these stars that might orbit
these supermassive black holes can
occasionally fall in. And when they get
sucked in, they get ripped apart. About half
of them falls into the black hole.
The other half gets shot out into interstellar
or even intergalactic space. What they found
is that essentially these streamers of
star stuff that escape the black hole can
collapse directly into planets on a
timescale of, you know, days or years.
Much, much faster than the tens of
millions of years that we think about
for the accretion of cores, the standard idea.
And so the idea is that these
things could be floating throughout the
universe, free floating everywhere.
Well not just floating around, we're talking
about shooting them across the universe
at millions of miles an hour so they
could be flying around like BBs or something.
That's right, that's right and
astronomers actually have looked and we
know that there is this
population of free-floating planets
out there in surprising numbers.
So a fraction of those could actually come
from the hearts of far distant galaxies
and burping black holes.
They could be anywhere! So for more planet news
and cosmology news and everything
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