SciShow Space is supported by Brilliant.org.
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On August 17, scientists detected something that sent the entire astronomy world into
a frenzy of data collection and analysis: a collision between two neutron stars — stars
so dense even the space between atoms has collapsed.
We knew that neutron stars could collide in theory, but this was the first time we’ve
ever seen it happen.
It was all made possible by the gravitational wave detector that made headlines last year
by proving the existence of gravitational waves — ripples in spacetime caused by some
of the most extreme events in the universe.
Like when two neutron stars crash into each other.
But astronomers were able to study this neutron star collision using more than just gravitational
waves.
They also observed it with different kinds of telescopes all over the world.
And this week, they released the first series of results in dozens of papers published by
thousands of authors in multiple journals.
So now we finally get to see what they’ve learned.
Turns out, it’s a lot.
Neutron stars are what’s left when a massive star, about 10-30 times the mass of our Sun,
explodes in a supernova.
In smaller stars, the core that’s left behind forms a white dwarf, but with stars this big,
the core itself collapses.
Electrons and protons combine to form neutrons, and everything gets crushed together until
it’s a giant blob as dense as an atomic nucleus.
A piece of neutron star the size of a sugar cube would weigh as much as Mount Everest.
That’s how dense they are.
Except they also tend to be about 20 kilometers in diameter.
Now imagine two of these things /colliding/.
I know cool guys don’t look at explosions, but even The Lonely Island guys would want
to see this one.
The collision was first spotted by LIGO, the gravitational wave detector, which detected
100 seconds’ worth of waves.
But even though it was only the fifth time we’ve ever detected gravitational waves,
that was almost the /boring/ part.
Scientists would have expected gravitational waves from an event like this.
What was exciting was that this was the first time we detected them from something other
than black holes merging, something we could see with telescopes, too.
By searching with those telescopes, astronomers were able to pinpoint exactly which galaxy
the waves were coming from: NGC 4993, about 130 million light-years away.
That meant we could get our first close-up look at the explosion of radioactive material
produced by a neutron star collision, what’s known as a kilonova.
And there was a lot to see!
The kilonova put out everything from X-rays to visible light to radio waves.
And, two seconds after that initial detection of gravitational waves, we also detected a
gamma-ray burst.
Astronomers had predicted that neutron star collisions would produce tons of radiation
because as neutrons were ejected in the collision, they’d form large atomic nuclei.
Some of those nuclei would be radioactive and decay right away, producing radiation.
And that’s exactly what we saw.
We also discovered that neutron star mergers are one of, or most likely the major process
that forms the heavier elements in the universe.
Until now, this was entirely theoretical.
We knew that elements lighter than iron could form in supernovas, but nothing heavier than
that.
The math said heavier elements like gold and platinum could form in a neutron star merger
like this, but we could have easily been wrong.
But the observations confirmed we got it right.
This one collision could’ve produced up to 100 times Earth’s mass in gold.
So that’s another giant mystery solved.
Then there was that short gamma-ray burst: a bright flash of the highest-energy form
of light.
We’ve detected many of these before, but couldn’t prove what was causing them.
Neutron star collisions were one of the possibilities, and this all but nails it.
We saw a short gamma-ray burst from what we know was a neutron star collision.
And these are just a few of the most important discoveries.
This was our first chance to prove a lot of stuff that physicists had predicted for decades:
gravitational waves, kilonovas, the creation of heavy elements, gamma ray bursts.
It all checks out.
With one event, we went from no direct evidence for many of these predictions, to really solid
evidence.
There’s an enormous amount of new research coming out of this, and a ton of things astronomers
are still hoping to figure out, like what happened to the neutron stars after they collided.
And this is only the beginning.
As we get our new gravitational wave detectors up and running, astronomers expect to spot
plenty more of these collisions, along with other types of gravitational waves, just in
the next few years.
We’re going to be learning a lot more about the universe pretty soon.
And here at SciShow Space, we’ll keep you updated every step of the way.
If you’re as excited as we are about this new era of gravitational wave astronomy, you’ll
probably have fun going through Brilliant.org’s astronomy lessons.
There’s one called the Life Cycles of Stars, and there’s this interactive quiz about
stellar remnants.
And today seems like a good day to give it a try, so let’s check it out!
Something that I hadn’t really expected before I dug into Brilliant is the really
good writing and story elements of these problems that they’re setting up.
In the Stellar Remnants lesson, the explanation reads kind of like a really dramatic ‘Goodnight
Moon’, but it’s more ‘Goodnight Sun’ which is super sad.
So it gives you a lot of information, but in this really poetic, beautiful way, and
then it jumps in and gives you these problems to solve, and it gives you a little bit of
information that you’ll need to solve the problem.
So I’m pretty sure that a white dwarf is 100,000 times more dense than steel, and I
got it right!
Thanks SciShow Space!
So the first couple of problems that you work through in a lesson give you a lot of information,
and then as you keep going, you’ll see that they give you a little bit less information
because you’re building up your skills, which is pretty fun.
So I won’t give away all the answers, but if you want to check out Life Cycles of Stars,
you should click on the link in the description!
The first 200 to go to brilliant.org/scishowspace will get 20% off their annual subscription.
And it’s really fun, and you’ll be helping out SciShow Space!
Thanks!
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