[ intro ]
Just in case you need something to keep you
up at night.
we can’t see them directly,
astronomers estimate our galaxy is peppered
with anywhere from ten million to a billion
black holes.
They’re all remnants of stars
whose cores collapsed into infinitesimally
small points.
And while each is bizarre and braain-bendy
in its own way,
models tell us that these objects at least
have limits.
But, then again… our models are sometimes
wrong.
Like, picture a star with a composition similar
to the Sun’s,
but much bigger.
According to models,
the biggest black hole made from a single
star like that
couldn’t exceed twenty-five solar masses.
Except…
astronomers just found one weighing in at
more than twice that.
They published their mystery last week in
the journal Nature.
And it might require rethinking exactly how
massive stars evolve.
This black hole was found while astronomers
were looking
at data from a star about eight times more
massive than the Sun.
It’s called LB-1,
and the paper’s authors calculated
that it’s roughly fourteen thousand light-years
away.
Based on patterns in the star’s light,
they found that the star was moving —
getting closer to, then farther from Earth
over a period of about seventy-nine Earth
days.
That indicated it was orbiting something.
Something the team couldn’t detect.
Still, even though they couldn’t see the
mystery object,
they could use data from LB-1 to estimate
its mass.
And the results were pretty telling.
Based on the calculations, the smallest possible
mass for this object
— just based on how the star was moving
—
was about six solar masses.
Technically, that means it could be star.
But a star that massive would be bright enough
for us to detect it.
So, instead, the team proposed
this companion had to be a black hole.
After analyzing more data,
they estimated that the actual mass of this
thing
is between fifty-five and seventy-nine times
the mass of our Sun.
And that’s where things get messy.
Because those numbers are more than twice
the mass
we thought possible given the black hole’s
surroundings.
See, both LB-1 and the surrounding area contain
a decent amount of elements other than hydrogen
and helium.
And according to models,
single stars can’t form huge black holes
in that kind of environment.
They should lose too much material at the
end of their lives.
So if they do become black holes, they should
peak around twenty-five solar masses.
Not fifty-five to seventy-nine.
So this discovery might mean we need to go
back
and modify our models for how stars evolve.
But it may also mean that something else is
going on.
For instance, the authors of this paper have
suggested that, well,
maybe LB-1’s black hole didn’t come from
a single star after all.
Maybe, this system used to have three stars
—
but after one collapsed into a black hole,
it ate one of the remaining two.
Alternatively, maybe there are two, less-massive
black holes here,
and they’re orbiting each other so closely
that we can’t tell them apart.
Of course, it could also turn out that the
distance measurements of LB-1 are incorrect,
since some of the team’s data do disagree
with other sources.
And that would seriously mess up the math.
But regardless of how that plays out, this
black hole will still be special.
Right now, it’s the only stellar-mass black
hole
we’ve found that can’t be observed in
the X-ray part of the electromagnetic spectrum.
That means it’s not stealing gas off its
companion star,
and it’s not actively consuming matter.
So this discovery could mean
there’s an entire population of these secret
black hole companions,
just waiting to be found.
In other black holes news, a group of astronomers
published a paper last week in The Astrophysical
Journal with evidence that planets
— planets! — could apparently form around
supermassive black holes.
And I don’t mean, like, the black hole’s
gravity captured them.
I mean planets could form around black holes
like they do around stars.
Just when you think you understand the universe,
black holes show up and ruin everything!]
It does give me context though,
I’m glad that our planet is orbiting ‘not
a black hole’
According to the paper, the action happens
in what’s called
the circumnuclear disk.
This is a thin disk of dust and gas a ways
away from the black hole —
much farther than the accretion disk that
feeds the thing.
Out there, the black hole’s gravity isn’t
overpowering,
so particles could collect into a giant ball
of rock.
But if you’re going to make a planet around
a black hole,
you don’t just need distance.
Your circumnuclear disk also needs to be dense.
Partly because, well, you need a lot of stuff
to make a planet.
But also, because you need something to block
radiation from the accretion disk.
Otherwise, the outer region of the circumnuclear
disk will be too hot,
and grains of ice and dust won’t be able
to stay solid and bind together.
In theory, black holes should be able to check
these boxes, no problem.
But in the new paper, one team decided to
actually test this.
They applied current models for planetary
formation to the circumnuclear disk of a supermassive
black hole that was actively eating matter.
And their model generated eighty-five thousand
planets,
each about ten times the mass of Earth and
orbiting at various distances.
Admittedly, the planet-making process didn’t
happen quite like normal.
Among other things, the planets took about
four hundred million years to form,
which is several times longer than what happened
in our solar system.
But hey, they formed around a supermassive
black hole.
It makes sense that things would happen differently.
These results are amazing to think about,
but they only came from a model.
We’re still a very long way from finding
planets like this — if they’re really
out there.
After all, it was only this year that we managed
to image the shadow of a supermassive black
hole.
Finding a planet amongst all of that will
be way more difficult.
The authors actually point out the usual methods
of finding planets are,
and I quote, “hopeless.”
But there could… maybe… possibly…
be something in X-ray or radio wave data.
Still, when you think about it,
it used to be impossible to detect any planets
around other stars —
so who knows what we’ll be capable of in
the future?
Thanks for watching this episode of SciShow
Space News!
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