Black holes as weapons - easy way to calculate the evaporation blast

[Melbourne Guy]

I've decided my latest novel uses black hole bombs, which aliens create by a mechanism unknown, and which are small enough to quickly evaporate to blast ships in the vicinity.

Knowing it is sci-fi and doesn't have to be perfect, about how fast do BHs evaporate? Alternatively, if I need them to last minutes to an hour, how large would they need to be?

And I'm assuming the 'blast' is a blip of radiation, but how much narrative license is there in that? Are we talking a lot of energy, or just a little as they evaporate back to nothingness?

 

[Vanadium 50]

It won't work like you think. Black holes of masses ~100's of tons have power output comparable to nuclear weapons for seconds, rather than nanoseconds. They will be billions of times as destructive. They are not like depth charges.

 

[Melbourne Guy]

They will be billions of times as destructive.

Thanks, @Vanadium 50, but that's actually better.

It won't work like you think.

You've got that right And while I'd like the physics to be as realistic as possible, the story has general purpose AI, FTL, and aliens, so it's already well beyond the universe as we know it. But I've no idea how evaporating black holes work aside from pop-sci articles.

They are not like depth charges.

I'd not though of depth charges. One of the grumpy ship AIs equates them to mines, but I'm thinking your idea is better. So, with your permission...and acknowledging that it is against your advice...I would like to appropriate it.

 

[Vanadium 50]

Some numbers -

At 6000K (solar temperature), you have a BH putting out microwatts of power (because the surface is so small) and lasting essentially forever (because its not putting out any power)

A 100 ton BH will convert all of its mass to energy in about 5 milliseconds, pumping out multi-TeV scale gammas. It would have 0.1% of the luminosity of the entire sun focused to a point. It would be millions of megatons.

As far as phsyics, the same magic that let's you make these tiny black holes let's you keep them stable until you want them to go kaboom.

 

[Melbourne Guy]

A 100 ton BH will convert all of its mass to energy in about 5 milliseconds, pumping out multi-TeV scale gammas. It would have 0.1% of the luminosity of the entire sun focused to a point. It would be millions of megatons.

You're a champion, @Vanadium 50, that's exactly the type of horrific energy output that makes for a gripping sequence, thank you

 

[Algr]

You need to explain how the aliens survive having made such a thing in their ship. And what energy source allows them to drag 100 tones of matter around space to crush into a black hole as needed. The .1c cannonball might be more plausible, as this would not waste most of its energy before hitting its target.

 

[Melbourne Guy]

You need to explain how the aliens survive having made such a thing in their ship.

Hi @Algr, I try and keep my aliens inexplicable, but it's not a total surprise that they're flinging little BHs around, they use a big one to cloak their entire civilisation in an FTL bubble. However, I'm unlikely to elaborate the mechanism for their magic weapons, I just need the aliens to have sufficient chinks in their armour to be defeatable for the purpose of the story

 

[Vanadium 50]

You need to explain

"To suggest is to create. To define is to kill." - Stephane Malarme.

 

[Algr]

Hi @Algr, I try and keep my aliens inexplicable, but it's not a total surprise that they're flinging little BHs around, they use a big one to cloak their entire civilisation in an FTL bubble. However, I'm unlikely to elaborate the mechanism for their magic weapons, I just need the aliens to have sufficient chinks in their armour to be defeatable for the purpose of the story

Perhaps, but you still might get into problems where if your Aliens can do X, why would they ever need Y. So using plausible physics can actually help prevent story problems. Why use the black hole gun when the politics ray is so much cheaper? Suddenly everyone votes the Aliens into office!

 

[Hornbein]

Perhaps, but you still might get into problems where if your Aliens can do X, why would they ever need Y. So using plausible physics can actually help prevent story problems. Why use the black hole gun when the politics ray is so much cheaper? Suddenly everyone votes the Aliens into office!

"Don't blame me. I voted for Kang." -- Homer Simpson

 

[Melbourne Guy]

Perhaps, but you still might get into problems where if your Aliens can do X, why would they ever need Y.

Oh yes, I've written myself into corners before, @Algr, and it's annoying to discard chapters and wind the story back to fix the problem. But it's speculative sci-fi, so it happens, and my aliens are generally cyphers, used to trigger reflection of the human condition. In this case, they're testing us by deploying various weapons systems to see how we'll respond...not that we know that, it's mayhem in the fleet when the depth charges (still tickled by that, @Vanadium 50) start to pop into their path. Especially as they're nowhere near the worst that the aliens can deploy.