We’ve spent quite a few episodes on what happens when massive stars fail as supernovae.
Here’s a quick recap.
A star with more than 8 times the mass of the Sun runs out of usable fuel in its core
and collapses in on itself.
The enormous amount of matter falling inward creates a dense remnant, like a neutron star
or a black hole.
Oh, and an insanely powerful explosion, visible billions of light-years away.
There are a few other classes of supernovae, but that’s the main way they go out.
But it turns out some supernovae just don’t bring their A-game.
Instead hitting the ball out of the park, they choke up at the last minute.
They’re failures.
They’ll never amount to anything.
They’re a complete and utter disappointment to me and your mother.
Oh wait, we were talking about stars, right.
So, how does a supernova fail?
In a regular core collapse supernova, the infalling material pushes the star denser
and denser until it reaches the density of 5 billion tons per teaspoon of matter.
The black hole forms, and a shockwave ripples outward creating the supernova.
It turns out that the density and energy of the shockwave on its own isn’t enough to
actually generate the supernova, and overcome the gravitational force pulling it inward.
Instead, it’s believed that neutrinos created at the core pile up behind the shockwave,
and give it the push it needs to blast outward into space.
In some cases, though, it’s believed that this additional energy doesn’t show up.
Instead of rebounding from the core of the star, the black hole just gobbles it all up.
In a fraction of a second, the star is just… gone.
According to astronomers, it might be the case that 1/3rd of all core collapse supernovae
die this way, which means that a third of the supergiant stars are just disappearing
from the sky.
They’re there, and then a moment later, they’re not there.
Seriously, imagine the forces and energy it must take to swallow an entire red supergiant
star whole.
Black holes are scary.
Astronomers have gone looking for these things, and they’ve actually been pretty tricky
to find.
It’s like one of those puzzles where you try to figure out what’s missing from a
picture.
They studied images of galaxies taken by the Hubble Space Telescope, looking for bright
supergiant stars which disappeared.
In one survey, studying a large group of galaxies, they only turned up a single candidate.
But they only surveyed a handful of galaxies.
To really get serious about searching for them, they’ll need better tools, like the
Large Synoptic Survey Telescope due for first light in just a few years.
This amazing instrument will survey the entire sky every few nights, searching for anything
that changes.
It’ll find asteroids, comets, variable stars, supernovae, and now, supergiant stars that
just disappeared.
We’ve talked about failed supernovae.
Now let’s take a few moments and talk about the complete opposite: super successful supernovae.
When a star with more than 8 times the mass of the Sun explodes as a supernova, it leaves
behind a remnant.
For the lower mass star explosions, they leave behind a neutron star.
If it’s a higher mass star, they leave behind a black hole.
But for the largest explosions, where the star had more than 130 times the mass of the
Sun, the supernova is so powerful, so complete, there’s no remnant behind.
There’s an enormous explosion, and the star is just gone.
No black hole ever forms.
Astronomers call them pair instability supernovae.
In a regular core collapse supernova, the layers of the star collapse inward, producing
the highly dense remnant.
But in these monster stars, the core is pumping out such energetic gamma radiation that it
generates antimatter in the core.
The star explodes so quickly, with so much energy, it totally overpowers the gravity
pulling it inward.
In a moment, the star is completely and utterly gone, just expanding waves of energy and particles.
Only a few of these supernovae have ever been observed, and they might explain some hypernovae
and gamma ray bursts, the most powerful explosions in the Universe.
Beyond 250 times the mass of the Sun, however, gravity takes over again, and you get enormous
black holes.
As always, the Universe behaves more strangely than we ever thought possible.
Some supernova fail, completely imploding as a black hole.
And others detonate entirely, leaving no remnant behind.
Trust the Universe to keep mixing it up on us.
Any other strange stellar objects that fascinate you?
Let me know in the comments and I’ll cover them in a future episode.
In our next episode, I answer the question: “why should we explore space when we haven’t
cleaned up the Earth first?”
Make sure you stick around for the blooper at the very end.
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And specifically, thanks to Yvonne Hodgson, Tombal Kerman, Clem Unger, and Eddi.
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