# Antimatter Black Holes?

1. Nov 23, 2013

### guysensei1

Can they exist?

What happens when an antimatter black hole and a normal black hole collide?

2. Nov 23, 2013

### Staff: Mentor

Sure, if enough antimatter was able to clump together. (Which, as far as we know, can't happen due to the huge imbalance between the amount of matter and antimatter in the universe)

If they collide, they just form a bigger black hole. No crazy explosion or anything like that.

3. Nov 23, 2013

### Chronos

The event horizon shields a black hole from interacting with the external universe save gravity. Unless anti matter has anti gravity properties [unlikely], it is impossible to tell one from the other.

4. Nov 24, 2013

### bahamagreen

Chronos:"...it is impossible to tell one from the other."

Let's make a convention for describing a charged black hole.

[m=matter/a=antimatter][BH][charge=+/-][excess/deficit=particle</>particle]

where the excess or deficit charge particle is
p=proton
e=electron
ap=antiproton
ae=antielectron

So we get these possible charged BH descriptions:

mBH+p>e = matter BH with positive charge due to more protons than electrons
mBH-p<e = matter BH with negative charge due to fewer protons than electrons
aBH-ap>ae = antimatter BH with negative charge due to more antiprotons than antielectrons
aBH+ap<ae = antimatter BH with positive charge due to fewer antiprotons than antielectrons

In all cases where the charge is the same polarity, the responsible particle sets of more and the sets of fewer are comprised of particles of different masses. For example, for the two positive charged BH configurations, one is caused by more protons and the other is caused by more antielectrons.
For the same charge polarity and magnitude, the same number of particles (p or ae) comprises the magnitude of the charge, but these particles have different masses in the two cases, likewise with the two negative charged BH cases.

To test the matter/antimatter attribute of a charged black hole, couldn't one toss in a known number of charged particles? The change in mass would just be the mass of the added particles as any annihilation of mass would go to equivalent energy, but wouldn't the charge change differentially because an annihilation would cause the lost particles to no longer contribute charge?

If so, then tossing buckets of N of p, e, ap, and ae into the four types of charged BH should do this:
(where + and - indicates the direction of charge change)

mBH+p>e = [+,-,-,+]
mBH-p<e = [+,-,-,-]
aBH-ap>ae = [+,-,+,-]
aBH+ap<ae = [+,-,+,+]

All four results are different, so why wouldn't this method indicate the matter / antimatter attribute of a BH?

I must be missing something... ;)

5. Nov 24, 2013

### Hornbein

So you toss anti-matter into the black hole. Its gravitation would always increase by the same amount that the equivalent in ordinary matter would have increased it. The change in the amount of charge would be the same as that caused by ordinary matter with that same amount of charge.

6. Nov 24, 2013

### Jonathan Scott

Total electrical charge is conserved regardless of the form of the charged particle.

7. Nov 24, 2013

### bahamagreen

Thanks for the replies...

Wiki states that when a charged particle and its antiparticle annihilate, both the mass and the charge annihilate.

I think my only assumptions are:
- that annihilation can occur inside the BH
- that annihilation of charged particles (those added and those already inside) changes the charge on the BH from what it was before adding the particles
- that the sketchy lack of rigor in my examples does not overlook some details ;)

Specifically,

Tossing antiprotons into a matter BH with positive charge would annihilate protons and make the net charge on the BH more negative.

Tossing antiprotons into an antimatter BH with positive charge would make the BH more positive because there would be no anihilation; neither the exiting antiprotons nor antielectrons would annihilate with the added antiprotons, so the antiprotons just add positive charge.

Tossing antiprotons into an antimatter BH with negative charge would make the BH more positive because there would be no anihilation; neither the existing antiprotons nor antielectrons would annihilate with the added antiprotons, so the antiprotons just add positive charge.

Tossing antiprotons into an matter BH with negative charge would annihilate protons and make the net charge on the BH more negative.

It looks to me like if you can measure the charge of a BH, you could toss in some antiprotons and see which way the charge changes. If the charge goes more positive, the BH is antimatter, if it goes negative, them the BH is matter.

Where does this go off course?

8. Nov 24, 2013

### Staff: Mentor

No, because you added negative charge with the antiproton, so you've canceled out the positive charge of the proton already and the resulting annihilation does not change that. You still make the black hole more negative, but that's because you've added negative charges, not because you've destroyed positive ones.

Antiprotons have a negative charge, so you'd make the black hole more negative like above.

9. Nov 24, 2013

### Hornbein

Antiprotons have negative charge. Any antiparticle has equal and opposite charge of its normal counterpart.

10. Nov 24, 2013

### Chronos

Just what do you think a proton is going to find to annihilate with when it crosses the EH? No particle survives an encounter with the singularity.

11. Nov 24, 2013

### bahamagreen

So, the problem is that whatever I toss in is not able to encounter any antipartners with which to annihilate?

Specifically, Chronos; there is no way for interactions and annihilations, etc. to occur between the EH and the singularity?

Or are you suggesting that the charge of a BH is an external attribute (based on what enters) and not on what happens inside (hidden interactions that can't influence the outside charge), or both, or neither, something else?

12. Nov 25, 2013

### Chronos

That is correct, all the particles that previously crossed the EH are no longer available for interaction.

13. Nov 25, 2013

### bahamagreen

If that is true, then why do accounts of what would happen passing through the EH of a big enouh BH suggest that there is nothing distinctive about the passage... that being inside the EH of a big enough BH would seem "normal" a least for a while - suggesting the continuation of normal interactions?

14. Nov 25, 2013

### Chronos

Well, you can't catch up with anything in 'ahead' [between you and the singularity], nor can anything 'behind' catch up with you.

15. Nov 26, 2013

### bahamagreen

OK, so everything going into the EH joins the local surface of a decreasing radius sphere that is cut off from the rest... I guess lateral interactions through the surface of the particular "generation" of sphere to which one attaches upon entry would still be possible... kind of trending toward 2D?

What happens to a single quantum particle - is its wave equation similarly restricted to one "layer of the onion" as it makes its way from EH to singularity?

The BHs seem to orchestrate a lot of principles that conspire to make them appear very simple from the outside.

16. Sep 19, 2014

### flowerdave

I think the interesting "stuff" would happen as the EHs made contact (I have no idea what that would/could look like). As far as the singularities themselves, whatever happened, (as long as it didn't propagate at greater than c) nothing would be observable outside the EH.

17. Sep 19, 2014

### vociferous

Nobody has a theory of quantum gravity so nobody can really say what form matter takes after the neutron degeneracy pressure is exceeded by gravitational pressure.

In GR, it is an infinitely dense singularity, but we know from quantum mechanics that such a thing is probably not physically possible. However, exactly what physics are going on behind the event horizon we cannot know, at least in the classical model of a black hole.

18. Sep 19, 2014

### Chronos

To the inquisitive, I would suggest reading up on black hole dynamics under GR. It's not an easy thing to calculate since most mainstream theories tend to blow up near the event horizon. You can derive all manner of weird things - like firewalls - if you are willing to blindly continue 'doing the math' at, or inside, the event horizon using conventional GR equations. I find that terribly unrealistic. A clear sign this is illogical is evident in the case of event horizons of SMBH's.