<p>Black holes are expected to evaporate due to Hawking radiation. Since Hawking temperature is inversely proportional to the mass of the black hole, as it would gradually lose mass with time they would evaporate more energetic photons. In the last moments, it would be able to evaporate into massive particles.</p>
<p>For example, they could evaporate into electrons. But if charge is conserved, shouldn't they emit positrons in the same amount of electrons? Or this is at random and therefore a black hole could emit more electrons than positrons? Also, could they emit high amounts of electrons? What about charged black holes?</p>

CC BY-SA 4.0
2024-08-13T01:05:30.440Z
FWIW, a BH has to be pretty small to emit electron + positron pairs, ~40 billion metric tons. See https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator
PM 2Ring
CC BY-SA 4.0
2024-08-13T01:31:40.547Z
@PM2Ring yes, it would be only so near the end of their "lives". But would they always emit the exact same amount of positrons and electrons? Or there is a probability that they may emit more electrons than positrons for example?
vengaq
CC BY-SA 4.0
2024-08-13T01:31:49.497Z
I *expect* that a neutral BH should remain neutral. OTOH, if you feed a BH normal matter and it emits equal amounts of matter & antimatter, you've changed the matter : antimatter ratio of the universe...
PM 2Ring
CC BY-SA 4.0
2024-08-13T02:12:21.827Z
@PM2Ring so a black hole that has fed on matter (not antimatter) should only radiate electrons? And how about a charged black hole?
vengaq
CC BY-SA 4.0
2024-08-13T06:03:15.440Z
No, it should radiate equal quantities of electrons and positrons. According to the [no-hair theorem](https://en.wikipedia.org/wiki/No-hair_theorem), it makes no difference what a black hole is formed from. Also see https://physics.stackexchange.com/q/772161/123208 & links therein.
PM 2Ring
CC BY-SA 4.0
2024-08-13T13:56:29.800Z
@PM2Ring so the emission of electrons and positrons has to be exactly 50-50 or is it a matter of probability? I mean, if the black hole emits at random whatever particle it can radiate according to the Hawking temperature, couldn't it be that by mere chance a black hole could radiate more electrons than positrons (or vice versa) even if it's not very likely?
vengaq
CC BY-SA 4.0
2024-08-13T15:28:22.310Z
Charge conservation is a very fundamental principal. See the questions linked here: https://physics.stackexchange.com/q/152825/123208 I'm pretty sure that Hawking radiation electrons and positrons must be created as pairs, but I'm not an expert in quantum electrodynamics. Note that Hawking's derivation is semi-classical, since we don't yet have a quantum theory of gravity.
PM 2Ring
CC BY-SA 4.0
2024-08-28T07:58:58.857Z
@PM2Ring There is no reason for Hawking electrons/positrons to escape to infinity in pairs. (The "pair creation" happens at the level of the virtual pair one being absorbed the other escaping.) There is still charge conservation, but it is the BH's charge that is changing. If the BH is charged this biases the chance of a charged particle escaping to infinity to particles with the same charge. This cause the process to average out to net neutral over time.
TimRias
<black-hole><hawking-radiation><thermodynamics><particles>
When a black hole evaporates in its last moments, will it emit the same amount of particles and anti-particles?
vengaq
# When a black hole evaporates in its last moments, will it emit the same amount of particles and anti-particles?

(Asked by: username_0 on 2024-08-12)

Black holes are expected to evaporate due to Hawking radiation. Since Hawking temperature is inversely proportional to the mass of the black hole, as it would gradually lose mass with time they would evaporate more energetic photons. In the last moments, it would be able to evaporate into massive particles.

For example, they could evaporate into electrons. But if charge is conserved, shouldn't they emit positrons in the same amount of electrons? Or this is at random and therefore a black hole could emit more electrons than positrons? Also, could they emit high amounts of electrons? What about charged black holes?

**Tags:** black-hole, hawking-radiation, thermodynamics, particles

> **Comments:**
> **username_1**: FWIW, a BH has to be pretty small to emit electron + positron pairs, ~40 billion metric tons. See https://www.vttoth.com/CMS/physics-notes/311-hawking-radiation-calculator  
> **username_0**: @PM2Ring yes, it would be only so near the end of their "lives". But would they always emit the exact same amount of positrons and electrons? Or there is a probability that they may emit more electrons than positrons for example?  
> **username_1**: I *expect* that a neutral BH should remain neutral. OTOH, if you feed a BH normal matter and it emits equal amounts of matter & antimatter, you've changed the matter : antimatter ratio of the universe...  
> **username_0**: @PM2Ring so a black hole that has fed on matter (not antimatter) should only radiate electrons? And how about a charged black hole?  
> **username_1**: No, it should radiate equal quantities of electrons and positrons. According to the [no-hair theorem](https://en.wikipedia.org/wiki/No-hair_theorem), it makes no difference what a black hole is formed from. Also see https://physics.stackexchange.com/q/772161/123208 & links therein.  
> **username_0**: @PM2Ring so the emission of electrons and positrons has to be exactly 50-50 or is it a matter of probability? I mean, if the black hole emits at random whatever particle it can radiate according to the Hawking temperature, couldn't it be that by mere chance a black hole could radiate more electrons than positrons (or vice versa) even if it's not very likely?  
> **username_1**: Charge conservation is a very fundamental principal. See the questions linked here: https://physics.stackexchange.com/q/152825/123208 I'm pretty sure that Hawking radiation electrons and positrons must be created as pairs, but I'm not an expert in quantum electrodynamics. Note that Hawking's derivation is semi-classical, since we don't yet have a quantum theory of gravity.  
> **username_2**: @PM2Ring There is no reason for Hawking electrons/positrons to escape to infinity in pairs. (The "pair creation" happens at the level of the virtual pair one being absorbed the other escaping.) There is still charge conservation, but it is the BH's charge that is changing. If the BH is charged this biases the chance of a charged particle escaping to infinity to particles with the same charge. This cause the process to average out to net neutral over time.  

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## 0 answers

