There are some crazy ideas for spacecraft propulsion out there, but tops among them
must be the idea to power an interstellar craft with a black hole.
Wait it gets crazier.
The black hole is made of light.
Yes, that’s right, a black hole, which is a region in space where the gravity is so
strong that, all together now: “not even light can escape,” very good, can itself
be made from light.
Theoretically, of course.
The black holes you’re probably used to are made of matter, and lots of it.
Stellar mass black holes usually form after giant stars go supernova and leave a core
behind.
If that core is more than about three times as massive as our entire sun, give or take
half a sun, its own gravity will crush the entire thing down to a single point, forming
a black hole.
However, because of Einstein’s equation E=mc2 we know that mass and energy are related.
It’s right there; energy equals mass times the speed of light squared.
So you could use energy to bend space into a black hole the same way nature uses mass.
You would just need an insane amount of energy to get the equivalent of enough mass, since
the speed of light is a huge number, nearly 300,000 km/s, and the equation calls for you
to square it.
Light carries energy, so if you managed to cram enough into a tiny space you would create
what’s called a kugelblitz, which is German for “Ball Lightning.”
The good news is if we wanted to make a kugelblitz we wouldn’t necessarily have to use the
equivalent of about three solar masses like nature needs for a stellar black hole.
We could make them much smaller, say one with the equivalent mass of two empire state buildings.
Then we would “only” need as much energy as our entire sun puts out in 1/10th of a
second.
We could use a laser to create this low mass kugelblitz, most likely one that shoots gamma
rays instead of visible light, since gamma rays are the most energetic electromagnetic
waves and we’re trying to be efficient in our ridiculousness.
If we managed to create this absurdly powerful laser, focused it at some point in space,
and pulled the trigger, we could create a tiny black hole, one with a radius smaller
than a proton.
A black hole this size would decay over the course of about five years, giving off hawking
radiation as it decays, and it might be possible to use that radiation to power a spacecraft.
I know, you’ve followed me pretty far down the rabbit hole already, but I promise it’s
just a little farther.
A 2015 paper proposed that if we could create a dyson sphere around our little kugelblitz
and harness the energy to propel a spacecraft, it could accelerate up to 72% the speed of
light before the black hole sputters out.
That is of course assuming the dyson sphere isn’t melted by the hawking radiation.
Or that the extreme heat generated from packing an insane amount of energy into a tiny space
doesn’t cause something unpredictable to happen.
A kugelblitz would be so hot that the math we use the predict the laws of physics doesn’t
apply, so we can’t accurately say how it would behave.
So black holes made from light and spacecraft that could harness them are still purely based
in theory.
Hypothetically they could exist, but I wouldn’t pin your dreams of interstellar travel on
them just yet.
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For more on Dyson Spheres, check out this episode of Space Crafts!
And one last thing.
There is another phenomenon called ball lightning, which is totally unrelated to a kugelblitz.
I bet that’s only confusing if you’re german.
Thanks for watching, and I’ll see you next time on Seeker.