# Couple of questions about black holes and event horizons

1. Apr 29, 2010

### Varine

Sorry if someone already asked these, but I didn't see anything that was the same.

A few of my friends are in a film class and we're working on a little indie movie, and the concept of it is a micro black hole is discovered at the edges of our solar system, and we want to make it somewhat realistic. So I'm hoping to get a bit of input on some of the things here to work on the script and visual elements and make it better.

Anyway, I know black holes are usually developed when a star's core collapses, but would there be any other possible cause? As it stands right now we don't really have much of an explanation for it (the script kinda skips over it, basically just says that it's more important to destroy it than figure out why it's there), which is fine since we couldn't find any other possible cause online and someone wants to use it as some statement that I forget what he said. I read that they may have formed during the cosmic inflation, but since that isn't really what's happening in our solar system it probably isn't a very good idea to say that's what caused it. We talked a little bit about it, and someone brought up an idea about a tear in the spacetime continuum linked this time dimension to one during the big bang, thus forcing the black hole to form (I personally liked the one where we didn't really say why it was forming because what he said made absolutely no sense to me).

Secondly, to destroy it, the ship drops basically a negative matter bomb close to the event horizon, with the plan that it would force the black hole to evaporate. But if it was dropped, when it hits the event horizon would it still be one object or would it start breaking down within the event horizon?

On a side note, if say part of the ship were to run into the event horizon but the rest was out, like an antennae or something, would it be broken off or would it pull the rest of it with it?

Another part of the story has them using the ergosphere to flip around, and using the acceleration as momentum for the return trip. So if they were to enter the ergosphere, would radio waves also be absorbed by the black hole and therefore distorted if they broke free from the ergosphere? And outside of the ergosphere, does it have any affect on objects? Could you remain stationary and not be affected by it's gravitational pull, or would you need to be a lot further away?

I think I'm forgetting some things that I meant to ask... but oh well. Anyone that can clear this up for me, it would be appreciated.

2. Apr 29, 2010

### Ich

How micro is that Black Hole supposed to be?
For example, a 50 million ton BH is about as large as a proton. You need some skill to maneuver the ship through its ergosphere.
Then, don't worry where the Black Hole is coming from as long as you don't have a reliable source for negative matter bombs. These things are much stranger than good old BHs.

3. Apr 29, 2010

### Varine

Well I guess not micro, but a stellar mass maybe. I did the equation Sr = 2Gm/c² using about half of a solar mass (1x10^30) and ended up with a Schwarzschild radius of about 1,483 meters, but since the mass was under the Chandrasekhar limit I figured it wouldn't be classified as a stellar mass.

4. Apr 29, 2010

### Ich

Ah. And you're trying to impress a solar mass black hole with a "negative matter bomb"?
Sorry, I don't have good ideas for your script from a physical point of view. To do something with a black hole, you need something with similar mass. If you want to trigger evaporationby something, I can't conceive of such a something. BHs are badass.

5. Apr 29, 2010

### Varine

Neither do I. I'm more hoping to get the other questions answered than that one, since if I understand the concept right, negative matter would move toward away from an object pulling on it instead of moving toward the force, in this case gravity, like matter would. Maybe we'll just throw words around to make it sound smart and hope most people won't know enough to actually make an argument against the concept. I asked about it a while ago and was referred to here: http://arxiv.org/abs/gr-qc/0402089

So would a phantom energy with an equation of state w<-1?

I read here http://arxiv.org/abs/astro-ph/0505618 that accretion of phantom energy would cause a BH to evaporate but they use a different equation of state.

I'll have to go to the library sometime and read more on it. I don't think we're going to go too in depth with the explanation because it's a movie and that would probably get relatively boring for most people, but I want to develop some kind of a remotely plausible idea for reference during dialog. And I have another question now:

Rotating black holes emit Hawking radiation theoretically, so does that mean that Hawking radiation would have a velocity above C in order to reach the required escape velocity of the EH? And am I right in thinking that the black hole itself is two dimensional, with no Z dimension being that it's an infinite mass compressed into a zero

As it stands right now, the only things I can think of would be to basically fill it with negative matter and cause it to evaporate, or use a form of phantom energy that would cause it to expand, disrupting the singular region and dissipating it. But would that actually cause it to dissipate or would it just expand infinitely without decompressing? Because really all you would need to do is decrease the gravitational field lower than C to allow particles to expand and that would destroy it right?

6. Apr 30, 2010

### Ich

Phantom energy is great. Cool name and sufficiently ill-understood that only very few peolpe could object for physical reasons. And a guarantee for a sequel, if they spill a few drops of it - you know, it will grow and grow...
All BHs emit Hawking radiation. And no, there's no easy way to understand it (like with "escape velocity"), it's a strange quantum effect.
I don't think you're right. But now that you ask, I don't know haw many dimensions the singularity has. It has no spatial dimension. The event horizon is (spatially) twodimensional like every surface.

Frankly, I have no idea. Maybe I'll read the papers you provided, could be funny.

Nope. The mass is already gone, away. You can't reach it anymore or somhow let it free. Neglecting the details, in a Newtonian sense you can think of it as all being in a single point. There's infinite negative potential, increasing it a bit would make no difference.

7. May 1, 2010

### Chronos

The least massive black hole detected to date is around 8 solar masses. That is intriguing given the most massive neutron star detected to date is probably no more than a couple solar masses.

8. May 1, 2010

### Varine

Yeah but unless it was incredibly large wouldn't be impossible to actually find given how far away they are?

9. May 3, 2010

### Chronos

The issue is the mass difference. We find many of each, but, few in between.

10. May 3, 2010

### IcedEcliptic

Is there a theory or two about why that is the case? Is it a result of the asymmetry of supernovae?

11. May 13, 2010

### Dr Chaos

I just thought I might contribute some calculations for you.

A black hole with a mass of 1*10^30 kg has:
- A lifetime of 1*10^71 seconds = 3.17 vigintillion years
- A temperature of 1*10^59 K

Hope this helps!

12. May 13, 2010

### Varine

How do they figure out the temperature?

13. May 13, 2010

### bapowell

The Hawking temperature is inversely related to the mass of the black hole:

$$T = \frac{1}{8\pi M}$$

14. May 13, 2010

### Varine

Okay, thank you.

A little bit unrelated to the other questions, but why are a lot of things covered with gold or a golden color? Like satellites and things that have that gold foil around a lot of it?

15. May 13, 2010

### IcedEcliptic

Effective insulation against temperature and some particulate bombardment.

16. May 13, 2010

### Varine

Well I mean, why isn't it white to reflect more of the light away?

17. May 13, 2010

### IcedEcliptic

Gold is a heavy metal, makes a good shield from charged particles, and is highly reflective. I don't know of a white material with the same properties, but the mylar backing is silvery and also insulating and reflective. Beyond that, heh, I am not a rocket scientist, but I am guessing some are here. You could start a thread and ask this question, yes?

18. May 17, 2010

### Ich

Gold is an extremely good reflector in the infrared region, where radiative heat transport happens. That's much more important than its behaviour in the optical region.

19. May 17, 2010

### IcedEcliptic

Of course, the optical permeability is what makes it so useful on space-suit visors. Win-Win!

20. May 19, 2010

### Dr Chaos

The formula I used was:

Temperature = 1026 M

Where M is mass in grams.