High School Do black holes radiate antimatter?

[friend]

I'm wondering if black holes radiate antimatter as well as matter? If they radiate antimatter in equal amounts to matter, then would it all cancel out?

 

[Drakkith]

I'm wondering if black holes radiate antimatter as well as matter?

My understanding was that they could radiate any type of particle, including anti-particles. The smaller the black hole, the larger the average mass of the radiated particles, so you won't see antimatter being radiated by any stellar mass black holes or larger.

If they radiate antimatter in equal amounts to matter, then would it all cancel out?

Would what cancel out? The amount of matter vs antimatter?

 

[rootone]

My understanding is that EM radiation (aka photons) do not have an antiphoton equivalent.
Photons are photons regardless of the state of matter that originated them.

 

[friend]

I suppose that black holes do radiate both matter and antimatter in equal amounts and that they do annihilate into photons leaving for the most part photons that radiate away from the BH. Is this right?

 

[Drakkith]

I suppose that black holes do radiate both matter and antimatter in equal amounts and that they do annihilate into photons leaving for the most part photons that radiate away from the BH. Is this right?

I'm not sure. I don't see right away why all of the particles and antiparticles are annihilating. They'd have to collide first. I'd expect to see some portion escape without colliding with its antiparticle. But, like I said, I don't really know.

 

[newjerseyrunner]

I'd be curious to know at what mass a black hole becomes significantly likely to emit an positron.

 

[friend]

As I understand it, there are virtual particle pairs formed just outside the BH horizon. Positive energy particles radiate out, and "negative energy" particles fall into the BH and reduce its total energy. My question is what's the difference between antimatter and negative energy particles? Antimatter is sometimes described as having negative mass or as traveling negatively through time. What constant gets the negative sign in negative energy particles?

 

[stefan r]

As I understand it, there are virtual particle pairs formed just outside the BH horizon. Positive energy particles radiate out, and "negative energy" particles fall into the BH and reduce its total energy. My question is what's the difference between antimatter and negative energy particles? Antimatter is sometimes described as having negative mass or as traveling negatively through time. What constant gets the negative sign in negative energy particles?

I'm not well educated on black holes. The "negative energy particles" are not real. I am more familiar with vacancies and holes which are also not real. For example we can put boron into a silicon crystal lattice. The "hole" is a point on the lattice missing an electron. Engineers talk about "holes" as if they were a thing and that works well for designing integrated circuits. A "hole" is not the same thing as an anti-electron or positron. Current really does flow through circuits when electrons and holes meet and annihilate each other.

I suppose that black holes do radiate both matter and antimatter in equal amounts and that they do annihilate into photons leaving for the most part photons that radiate away from the BH. Is this right?

My impression was that particles tunnel out of the event horizon. In order to escape from near the event horizon a particle must have near light speed velocity. So the particles do not escape they fall right back in. All types of particles radiate energy as they fall into a black holes.

The black hole losses mass from evaporation because energy and mass are interchangeable. Escaping photons carry away energy. Shining a light at a black hole will increase its mass.

 

[Nugatory]

I'm wondering if black holes radiate antimatter as well as matter? If they radiate antimatter in equal amounts to matter, then would it all cancel out?

Hawking radiation will contain both matter and antimatter in equal amounts, and it does not cancel out, because the particles and antiparticles both have positive mass-energy.

However, for any currently existing stellar-mass black hole the "equal amounts" are both zero, because the energy available for Hawking radiation is so small that only very long-wavelength low-energy photons have any probability of emission.

 

[stefan r]

... "equal amounts" are both zero, because the energy available for Hawking radiation is so small that only very long-wavelength low-energy photons have any probability of emission.

The probability of tunneling events is not zero. So, for example, the hydrogen atoms in your little toe could tunnel over and fuse with each other. That would result in a decent sized explosion. The odds are just so low that you might as well not worry about this problem. But the probability is greater than zero.

All of the mass/energy in a black hole is available. Odds of a tunneling event drop exponentially when you involve multiple particles in the event. (really exponential not the figure of speech). Also the distance has a strong effect on tunneling event probability. So the likelihood that an alpha particle tunnels out of a plutonium nucleus is much higher than the probability of a hydrogen nucleus tunneling into an adjacent atom. In stellar mass black hole the likelihood of a tunneling event crossing the event horizon is quite low despite the large amount of available mass. Our stellar mass black holes will be adsorbing cosmic background radiation faster than they will be emitting photons. They will grow until the universe and nearby space goes through a heat death.

In normal conversation it is probably best to avoid making a distinction between "not happening, zero", "so slow it takes a ludicrously long time to notice an effect", or "happening well below the background noise level". But this is a physics forum so I think the details are worthy of discussion.

 

[mfb]

As I understand it, there are virtual particle pairs formed just outside the BH horizon.

That is a pop-science myth. It is not what actually happens.

Antimatter is sometimes described as having negative mass

That is completely wrong.

All the black holes we know are so massive (3+ solar masses) that they only emit electromagnetic radiation with extremely low frequencies. There is a theoretical chance that they emit massive particles, but the probability that any black hole in the observable ever did that in the history of the universe is below 0.000000001%, so why bother.
At 10^-7 solar masses we get a few neutrinos in addition.
At 10^-16 solar masses or 10¹⁴ kg we get some electrons and positrons - in equal amounts for an uncharged black hole. A black hole with this mass has a Schwarzschild radius of just a few hundred femtometers, smaller than an atom.
At 10¹¹ kg we also get pions as the lightest hadrons. A black hole with this mass is smaller than a proton and emits Hawking radiation at a power of a few GW. It still has a lifetime of about a billion years.

Everything emitted will just fly away, matter and antimatter fly away in exactly the same way.

 

[stefan r]

...
Everything emitted will just fly away, matter and antimatter fly away in exactly the same way.

Why would it fly away instead of orbiting? How would a charged particle avoid interacting with nearby charged particles that are orbiting?

 

[mfb]

Why would it fly away instead of orbiting?

Hawking radiation is emitted. It flies away because otherwise it wouldn't be Hawking radiation. There is also no process that would lead to orbiting particles.

How would a charged particle avoid interacting with nearby charged particles that are orbiting?

That is a possible process if there is something orbiting the black hole.

 

[stefan r]

...There is also no process that would lead to orbiting particles...

I am missing something here. I thought the entire galaxy is orbiting a black hole. Radiation from accretion disks is emitted by particles orbiting.

 

[mfb]

I thought the entire galaxy is orbiting a black hole.

There is a central black hole, and a few stars are directly orbiting this central black hole, but the mass of the black hole is tiny compared to the total mass of the galaxy. Most parts of the galaxy wouldn't even notice if the central black hole wouldn't be there.

This has nothing to do with Hawking radiation, where things are emitted from the black hole.

Radiation from accretion disks is emitted by particles orbiting.

This has nothing to do with Hawking radiation either.

 

[stefan r]

This has nothing to do with Hawking radiation, where things are emitted from the black hole.This has nothing to do with Hawking radiation either.

A particles position is uncertain. Sometimes it finds itself in various places. A particle that was inside the event horizon and finds itself outside the event horizon is not going to behave any differently than other particles outside of the event horizon. If other particles near the black hole are orbiting and gradually making their way into the hole via friction then one of Hawking's particles does the same. We would only see Hawking particles escaping when we see other orbiting particles escaping.

Contrast with an alpha particle in radium. When the tunneling event happens there are two nuclei (radon and helium) with positive charges close enough to each other for electric repulsion but too far for nuclear binding. The nuclei they fly apart with high velocity. An alpha particle a short distance from a black hole will not feel a strong repulsion. There is no energy released by traveling up a gravity well.

 

[mfb]

A particle that was inside the event horizon and finds itself outside the event horizon

There is no such thing.

Hawking radiation is created outside.

If other particles near the black hole are orbiting and gradually making their way into the hole via friction then one of Hawking's particles does the same.

No. They travel in different directions, and at different speeds for massive particles. In addition, Hawking radiation for massive black holes is exclusively electromagnetic radiation, while the particles in the accretion disk are massive - there are no stable orbits for light.

 

[friend]

That is completely wrong.

I need some help understanding this negative energy going into the BH. I'm thinking that the Hawking radiation is similar to the Unruh radiation, both being produced by accelerated reference frames. Does Unruh radiation produce negative energy "particles"? What is negative energy? Isn't this the stuff needed to keep worm holes open for which we really have no hope of producing? Why not?

 

[mfb]

I need some help understanding this negative energy going into the BH.

There is no such thing.

Does Unruh radiation produce negative energy "particles"?

No.

What is negative energy?

It is unclear if things can have negative energy at all. Probably not.

 

[friend]

It is unclear if things can have negative energy at all. Probably not.

What about gravity? Doesn't gravity have "negative energy"? Would gravitons be particles with negative energy?

 

[Kevin McHugh]

There is no such thing.No.It is unclear if things can have negative energy at all. Probably not.

I must be deficient in my understanding of the negative energy solutions to the Dirac and KG equations. Do they not predict negative energy solutions?

 

[mfb]

What about gravity? Doesn't gravity have "negative energy"? Would gravitons be particles with negative energy?

Gravity is not an object. Asking about its energy is about as meaningful as asking about the energy of the concept of sweetness.

Gravitons, if they exist, have positive energy.

I must be deficient in my understanding of the negative energy solutions to the Dirac and KG equations. Do they not predict negative energy solutions?

Quantum field theory doesn't have these solutions any more, they are proper particles with positive energy.

 

[Kevin McHugh]

Gravity is not an object. Asking about its energy is about as meaningful as asking about the energy of the concept of sweetness.

Gravitons, if they exist, have positive energy.Quantum field theory doesn't have these solutions any more, they are proper particles with positive energy.

Thanks MFB. I probably need to read a good QFT book. Any recommendations?

 

[stefan r]

What about gravity? Doesn't gravity have "negative energy"? Would gravitons be particles with negative energy?

Apples grow in whole numbers. I can take 3 apples out of a basket. That is not the same as saying that "negative apples exist". Eating the apples is a type of negative apple production. We can prove that the operation (eating) is happening without having to believe that negative apples exist.

 

[friend]

It is unclear if things can have negative energy at all. Probably not.

So how do black holes evaporate? Is it simply matter inside quantum tunneling out?

 

[mfb]

The radiation is produced outside, simply because spacetime is curved there.

 

[friend]

The radiation is produced outside, simply because spacetime is curved there.

Yes, I understand this is similar to radiation associated with Unruh radiation and reheating after inflation. But if all that is produced because of curved space is positive energy particle radiation, then wouldn't some of this positive radiation fall into the BH and make it bigger?

 

[mfb]

No. Where would the energy come from to make it bigger?

 

[friend]

No. Where would the energy come from to make it bigger?

If all that is produced near the event horizon is positive energy particles, it seems natural to assume that some of them would fall into the BH and make it grow. Or are you saying in general that in curved spacetime the radiation that is produced always only goes in one direction wrt the curvature?

 

[mfb]

The energy to make these particles comes from the black hole mass - even if the particles could fall in they wouldn't change the energy there. And the particles can only leave anyway.