What Are Black Holes Made Of?
Black Holes are among the most fascinating
and mysterious objects in the known universe.
They’re thought to hold many secrets about
how space and time work, and some say that
they could even be used to create wormholes
through galaxies one day. But what creates
these incredible, destructive and iconic forces
of nature?
This is Unveiled and today we’re answering
the extraordinary question; What are black
holes made of?
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Black holes are so strange and powerful that
they can feel like an almost unreal concept
straight out of a science fiction novel. But
these things are definitely real, and they’re
crucial to our reality! Because of their mysterious
properties, though, scientists have trouble
even detecting them at all. They effectively
pull in all light that comes close, so the
only way to know a black hole is there is
to notice how it interacts with other matter
around it. Which means that if a black hole
ever wasn’t near anything else, then we’d
have no way to know that it’s there at all!
In fact, it’s thought that most stellar
black holes are isolated right now - impossible
to detect and therefore totally unknown to
us. It’s perhaps a scary thought for interstellar
space travellers of the future; that a black
hole they were oblivious to could unfortunately
consume them. Especially because black holes
aren’t exactly rare either… We can’t
count them directly, but we know they’re
formed from certain types of large star, leading
to estimates that there could be between ten
million and a billion black holes in just
our own Milky Way Galaxy.
Black holes form out of collapsing stars,
but not just any stars. Different stars go
through different processes depending on how
large they are, and only the most massive
form black holes at the end of their life
cycles. The stars are initially kept alive
by burning fuel in their core, but as soon
as they run out of fuel their own gravity
turns against them, causing them to implode
and eventually transform into a stellar black
hole.
But a stellar black hole is only one of three
types of black hole that scientists believe
exist. Another is primordial black holes,
which are thought to have formed right after
the big bang. These mind-boggling structures
are the smallest, and according to NASA are
the size of an atom with all the mass of a
mountain. But then there are supermassive
black holes which, as their name implies,
are extremely massive (potentially billions
of times as massive as our own sun). Even
the experts aren’t one-hundred-percent sure
how these things form… They could be the
result of thousands of smaller black holes
merging together, or just a single black hole
devouring much more matter than it can reasonably
handle. Other theories have supermassive black
holes forming out of dark matter but, in any
case, these vast and sprawling constructs
are usually found at the centre of galaxies.
Theoretically, there should exist a “middle
ground” between black hole types too - where
a black hole is bigger than stellar but not
so big to be categorised as supermassive - but
we haven’t conclusively proven it yet. So,
for now, science mostly sticks with the general
understanding that black holes are simply
formed out of stars; that at their beginning
they’re the product of supernovas.
But, can we truly say that black holes are
made of stars? Carl Sagan famously said of
human beings; “We’re made of star stuff,”
meaning that the elements that constitute
a human, such as carbon, hydrogen, nitrogen,
and oxygen, all came from stars going supernova
and spreading them across the universe. So,
in that sense we’re made of the same matter
that black holes are, and we’re both offshoots
of the same thing - a star’s self-destruction.
But there’s where the comparison between
us and a black hole ends. Because, while we
know lots about how the human body works,
we know very little about how a black hole
does… and we’re still not even close to
confidently knowing what happens at the centre
of one. The problem is that most of a black
hole isn’t really made of anything at all,
and that’s because any matter that gets
close enough is devoured... into apparent
nothingness. Black holes are, at their ominous
and unusual hearts, massive distortions in
spacetime. They pack large amounts of matter
incredibly densely into an inconceivably small
point. So much so that our understanding via
conventional physics breaks down near the
centre, or the singularity.
Turn the issue on its head, though, and we
could say that black holes are actually made
of anything and everything. They’re formed
out of collapsing stars, but stars form in
the first place from gases and collapsing
nebulas. These are fundamental, cosmological
processes but dial them back far enough and
they - along with everything else in the universe
- begin with the same raw materials. In theory,
then, if you had a way to compress matter
far enough, you could turn anything into a
black hole. It’s not at all likely, or even
physically, practically possible, but the
idea hinges on the concept of the Schwarzschild
Radius, proposed by Karl Schwarzschild, which
gives an equation to know how far down something
has to be compressed to form a black hole.
Ultimately, if an object is compressed to
the point where its physical radius is smaller
than its Schwarzschild radius, then it will
do exactly that!
So, extremely hypothetically speaking, anything
could be a black hole; buildings, cars, baseballs,
pencils, even humans ourselves if all of our
mass was compressed far enough. Earth could
become a black hole, but all of its mass would
need to be compressed down to a speck of just
8.7 millimetres before that happens… In
reality, though, we don’t have to worry.
There’s no conceivable way that an Earth-induced
black hole could happen in nature unless Earth
somehow grew far more massive than it currently
is. Even our own sun isn’t massive enough
to ever actually form one.
Not that such seemingly standard facts of
life have discouraged people from trying to
make tiny black holes of their very own - or
variations of. In 2016, for example, physicist
Jeff Steinhauer got around the apparent impossibilities
by creating imitation black holes in his laboratory
using sound waves - rather than light. A spot
out of which sound can’t escape, it’s
a simpler concept (relatively speaking) but
impressive nonetheless!
If anything, efforts like Steinhauer’s show
just how mysterious genuine black holes are.
Anything could be happening inside of one,
but there’s no way of getting even a glimpse
ourselves. What we do know is that black holes
are formed from regular matter initially,
but only when it forms into the universe’s
largest stars, and only when those collapse.
In the backs of the minds of most black hole
enthusiasts there is the question of dark
matter, but that’s another enigma entirely!
Until we can get to grips with that which
we can’t see, they’re the fascinating
product of perishing stars. And that’s what
black holes are made of.
What do you think? Is there anything we missed?
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