Black holes and dark matter are two topics that get science geeks pretty hyped, but sadly
they’re not usually mentioned in the same sentence.
Now though you can feel twice the hype, because a new theory has proposed that we can detect
dark matter using black holes.
Well, more accurately, using the gravitational waves that dark matter near a black hole would
give off.
So make that three times the hype.
I am 99.9% positive that all of you watching are familiar with black holes, the superdense
points in space where matter is packed so tight and gravity is so strong that -all together
now- not even light can escape.
You’ve probably also heard of gravitational waves.
First proposed by Einstein and confirmed in 2015 by the Laser Interferometer Gravitational-Wave
Observatory, or LIGO, they are ripples in spacetime and they’re caused when massive
objects turn space into a wibbly wobbly, timey-wimey...
Thing.
So far, these are well established phenomenon and we have a pretty good idea of what they
are and why they happen.
But the third member in this science love triangle is the biggest question mark of them
all: dark matter.
Evidence has shown that almost 85% of the matter in the universe is unaccounted for.
Beyond that, we have no solid lead what all that missing stuff actually is, so we just
call it ‘dark matter’.
One of the proposed culprits is a hypothetical subatomic particle called the axion.
These little guys were originally proposed to solve another mystery of physics called
the Strong CP Problem, but they might be the key to Dark Matter as well.
Score!
They’re predicted to be a billionth the mass of an electron or lighter, but with enough
of them they just might add up to all that missing mass.
Those are the key pieces: a black hole, gravitational waves, and a whole bunch of axions.
The way the researchers proposed they work together is really quite elegant.
Because the quantum world is a silly place, axion particles should also act like waves.
The lighter the particle, the longer the wavelength.
Hypothetically, if an axion is near a spinning black hole and its wavelength is as long as
the black hole’s diameter, then things could get really crazy.
That’s right we’re not even at the crazy part yet!
A phenomenon called superradiance can kick in.
Superradiance is a process that has been shown to multiply photons, and axions and photons
are thought to have some properties in common.
The spinning black hole would give the axion more energy and generate more axions in a
runaway chain reaction like a Mr. Meeseeks box.
You can end up with 1080 axions around one black hole.
That’s as many axions as there are atoms in the universe!
All these axions should give off a distinct signature that we can detect.
The researchers predicted they won’t scatter randomly, but will form orderly clouds like
electrons do around an atom.
And as they smash into each other, they should annihilate each other to produce gravitons,
another hypothetical particle that’s never been confirmed.
These gravitons mediate the force of gravity, so we should be able to detect them coming
from these huge axion clouds as gravitational waves.
LIGO isn’t quite sensitive enough to pick up these gravitational waves just yet.
But once it is, if LIGO detects gravitational waves with the same wavelengths from different
sources, then we’ll know it’s likely caused by these axions and all the pieces will fall
into place.
Don’t go thinking it fits completely perfectly just yet.
For the axions to have a long enough wavelength they’d have to be much lighter than what
we’ve been looking for with current lab experiments, anywhere from ten thousand to
ten million times lighter.
At that mass they still might be too light to account for all the dark matter.
So pump the brakes on the hype train just a little, and let’s wait until LIGO is a
bit more sensitive.
Do you have a favorite candidate for dark matter?
Axions?
WIMPs?
MACHOs?
Let us know in the comments, don’t forget to subscribe!
If you’re still hung up on why Gravitational Waves should get you hyped, check out Julia’s
video on it right here.
One more thing, we got nominated for a Webby for sending a VR camera to the edge of space
and you can help us win, all you have to do is go to vote.webbyawards.com, search Seeker
and click vote, simple as that or click the link down below.
And if you still haven't seen it, check out the video on Seeker VR.
Thanks for watching!