Black holes can become some of the most massive
objects in the universe.
A collision between two of them can cause
waves to form in the fabric of spacetime itself.
Theoretically speaking, though, black holes
have an opposite; white holes.
So, what would happen if these two structures
were to meet?
This is Unveiled and today we’re answering
the extraordinary question; What if a black
hole and a white hole collided?
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White holes are a currently hypothetical structure,
but they’re thought to work like an inverted
twin to Black Holes; to be their exact opposite
in nature.
A black hole attracts and devours matter;
a white hole repels and regurgitates it.
Nothing can escape a black hole, but nothing
can enter a white hole.
White holes essentially act as a black hole
would if video footage of it was played in
reverse, with matter being expelled from the
centre at the speed of light.
Despite their opposite nature, though, it’s
thought that white holes would look very much
like black holes from a distance - if we ever
were to observe one!
Although they are theoretically possible,
scientists don’t know how white holes would
form - if indeed they do.
We have a little bit more of an idea for black
holes, which often form when a massive enough
star loses enough of its fuel and explodes
into a supernova.
That event leaves an extremely dense core
behind… which assumes new shape as a kind
of tunnel in spacetime; a black hole.
White holes can’t form in the same way,
though, because their core has zero mass - so
they can’t exist with actual matter at their
centre.
In theory, if just one atom of hydrogen somehow
managed to enter a white hole’s singularity,
it would collapse.
Because they’re so unusual, some researchers
even believe that white holes could be the
key to understanding other mysteries like
dark matter; with one theory being that dark
matter is formed from microscopic white holes
ejecting it.
Despite the fact that white holes cannot have
mass in their singularity and constantly repel
matter from their core, however, it’s thought
they would have gravity… which means they
could attract objects from a distance.
So, if we assume for the purposes of the question
that white holes do exist, then a collision
between one and a black hole is possible.
If anything else - something less massive
- approached a white hole, like a planet or
a spaceship, then there’d really be no contest.
The route toward the white hole would be extremely
dangerous.
The matter being expelled from it is traveling
at the speed of light, meaning any object
that got close enough would be relentlessly
bombarded with incredible amounts of energy
probably in the form of gamma rays.
These would tear most objects apart, or at
least make it physically impossible to travel
any further.
Since no matter can reach the centre of a
white hole, there’d be a kind of cosmic
cut-off point where any object that tried
would be held at a distance by the repelling
forces at work… and would still be getting
blasted with wave upon wave of destructive
energy.
The situation changes, though, when that object
is a black hole.
Now we have the ultimate example of two opposites
attracting and an extreme case of energy transference.
Since the white hole is constantly ejecting
matter and the black hole is constantly causing
matter to fall into it, the white hole would
end up feeding the black hole like water down
a drain.
It’d be one-way traffic, but accelerated
to unimaginable speeds.
A black hole that’s endlessly “fed”
in this way could well grow larger and larger,
to eventually form an exceptionally massive
supermassive structure.
It would be a battle which could rage for
thousands of years, with both objects promising
an infinite resource… but given what we
know about black holes and what we don’t
know about white holes, in time the black
hole could become massive enough to engulf
even its bottomless provider of matter to
consume.
It’s possible that it would outlast the
white hole, and the white hole would disappear.
If this were to happen, it’s truly unknown
what would happen next.
We’re still not exactly sure where non-theoretical,
conventional matter goes when it enters a
black hole… so predicting the ultimate fate
of a hypothetical construct is even harder
still.
Due to Hawking Radiation, the black hole should
eventually shrink and eject the matter from
natural decay, but some scientists think that
there’s more to it than that.
It’s argued by some that matter entering
a black hole is totally isolated and altogether
disappears from the universe.
It’s actually because of this that some
theories suggest that black holes are already
connected to white holes in other universes
by a tunnel they form between each other in
spacetime.
When a black hole devours matter in one universe,
that matter could be ejected out into another
via a white hole - meaning infinite matter
goes in, and infinite matter comes out.
To make that particular idea just a little
stranger, some even theorize that white holes
are actually older than our universe, and
that the connections between multiple universes
via black and white holes could explain the
beginning of our own reality.
But the encounter doesn’t (or needn’t)
end there.
In a different scenario, the black hole could
in theory expire through Hawking radiation
before consuming the white hole.
In this way, the white hole will have trumped
its counterpart by effectively “overfilling”
it.
Equally, though, even were the black hole
to win in the initial collision, then time
could eventually tell a different story.
Theoretical physicist Carlo Rovelli proposes
that when black holes decay and ultimately
die, they create white holes in their wake.
When black holes lose enough mass via Hawking
Radiation, they’re more traditionally thought
to shrink until they vanish.
But that’s a problem in some models of the
universe because there should be an “other
side”.
For Rovelli, then, a black hole wouldn’t
simply evaporate into nothing, but would instead
rebound when it becomes too small - and that
rebound produces a white hole.
Rovelli also suggests that this would be an
exceptionally slow process - potentially taking
millions of times more than the age of our
universe to complete, were the original black
hole to be about the mass of the sun.
The also currently hypothetical primordial
black holes, though, are much smaller… so
Rovelli also notes how it could be that the
primordial black holes theoretically created
at the beginning of the Big Bang have already
been able to die and form white holes since
the start of the universe.
If that’s true, then we’re suddenly contemplating
much more than one isolated cosmic collision.
Even were the black hole to overcome its opponent
in that particular event, achieving an incredible
size in doing so, it could still be survived
by the very structure it had just consumed.
And, over time, more and more of the universe’s
black holes would go through a similar transformation,
leaving the cosmos littered with multiple,
unknowable, enigmatic points all ejecting
matter back out into it.
Space would then be shaped by white holes.
All of that said, it pays to keep in mind
that this particular hypothetical comes with
a sizeable caveat; that the basic existence
of white holes is still very much up for debate.
Our current understanding of the universe
means they’re possible, but plenty of physicists
still argue that they’re unlikely to form
in nature…
On the one hand, weird and wonderful features
of the universe like gamma ray bursts could
actually be white holes (we just don’t know
it yet).
On the other, we could simply be pondering
a plain impossibility.
But that’s what would happen if a black
hole and a white hole collided.
What do you think?
Is there anything we missed?
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