Can a Black Hole Be Weaponized?

[Dmitry67]

The very calculation for the Schwarzschild radius are done in stars rest frame

If the same star is flying by at very high speed, it is in fact Lorentz-contracted, but, the same math is no longer applicable for the Schwarzschild radius! The solution is now dynamic (as star is flying) and it becomes very different because in General Relativity gravity is not created by mass but by stress energy tensor, which insludes rest mass as just one of its components.

Example: photon gas. Rest mass: zero. But it creates gravity because it has pressure.

 

[Dmitry67]

Oversimplification. Flying object has less gravity.

Imagine 2 objects flying in parralel at very high speed. In their own rest frame they attract to each other. However, when they fly by there is a time dilation, so they attract slower, so external observer concludes that the force between them is weaker.

Again, it is an oversimplification.

 

[Dr Chaos]

Okay, I understand now. Thanks to everybody who posted.

However, I do have another question. If the bullet is a black hole in its resting frame of reference (i.e. so it is actually a black hole), and if I was to accelerate it, what would its behaviour be like in Earth's atmosphere? Would it slow down quickly or could it maintain a constant velocity?

 

[Dmitry67]

Black hole in a gas?
In would 'eat' all gas around it, it mass would increase, and it would slow down (because momentum is conserved). However, very soon it will create powerful jets from the poles. These jets will be very intensive. They will carry away the momentum affecting the trajectory of the black hole.

 

[Ich]

Would it slow down quickly or could it maintain a constant velocity?

It would nor slow down appreciably, it has too much mass.

 

[dgtech]

Even if you manage to create a small black hole, it will saturate pretty soon and will decay

IMO there is a wrong concept a black hole would just churn away all mater, remember - the black hole is condensed matter to a point it's density becomes critical. IF you add rapidly material the overall density will decrease and it will no longer be a black hole.

Black holes in space are gradually assuming matter in the form of subatomic particles, but that's after the actual black hole has accumulated enough matter to "grow" big enough to be able to break down a planet from distance with its immense gravity and then grind all particles that fall in it's event horizon so immensely that creates those powerful jets of high intensity radiation. Those holes are billions of years old, and a newly created black hole, exposed to conditions different than billions of years ago, will behave differently.

You can burn away the whole planet and still won't release enough energy that would be enough for a practical black hole weapon. You can ease kinetic through chemical energy much more efficiently, and obliterate a whole planet with a fraction of the energy requirements of a black hole weapon, plus why wasting the precious chemical resources and creating a potential danger to us in the long run.

On the other hand, a controlled black hole, just like a controlled nuclear reaction, can be potential safely contained and regulated through the rate matter is fed to it, and the excess radiation harnessed as an energy source. After the black hole begins to be uncontrollable, it gets quickly stabilized and sent into deep space to act as a gravity well for a star base :) It can also be accelerated into orbit to act as a gravity lift over a specific part of the planet, creating fancy hanging rocks with forests on them, like in Avatar ;) Why not even an orbital gravity assist booster made of several such objects, or cleaning sentinels for all the space junk we've made that makes frequent going in and out the planet risky.

Many good practical uses of a black hole, the byproduct could potentially be used also for bad purposes I guess, but why being so mean and wasteful :)

 

[Dmitry67]

IMO there is a wrong concept a black hole would just churn away all mater, remember - the black hole is condensed matter to a point it's density becomes critical. IF you add rapidly material the overall density will decrease and it will no longer be a black hole.

No.
Density is irrelevant.
Schwarzschild radius is proportional to the mass.

r = 2GM/c^2

Say, Schwarzschild radius of Earth is 1cm. In fact, you must compress Earth to enormous density to create a black hole!

But now increase Earth radius by x10 kkeeping the same density. Now Earth is 10 times bigger, and 1000 times heavier. The Schwarzschild radius is now 10meters! So it contains 10^9 more volume for 10^3 more mass. So the 'critical' density is now 1000000 times less!

So look at the formula. It not about the density, it is about mass. You can make Black hole of ANY material: water, gas, or even interstellar gas with 1 atom per cubic meter without compressing that matter, but using it 'as is'

In another words, if you add more and more material to an object, keeping the same density, the Schwarzschild grows much much faster than normal radius, so Schwarzschild always catches up with the real one and object becomes black hole.