# What happens to the electrons in a black hole?

1. Apr 3, 2015

### jimmylegss

As multiple stars would collapse into a black hole, are the electrons shot outwards? Or are they converted into mass with infinite density (what a black hole is right?)

Thanks.

2. Apr 3, 2015

### Khashishi

Presumably nothing happens to them right when they pass through the event horizon. But current physics is not advanced enough to predict what happens when they reach the center singularity. Probably, a mature theory of quantum gravity is needed.

3. Apr 3, 2015

### Staff: Mentor

No, that's not what a black hole is. A black hole is the region of spacetime around a sufficiently dense object, and an electron falling into it is no different than any other particle, or larger object for that matter - it falls in, it doesn't come out.

If you take the equations of general relativity completely at face value, they do say that everything inside the black hole ends up concentrated in a single infinitely dense point at the center of the black hole... but no one seriously believes that that's really what's going on. Instead, we take the infinite density that shows up in the solution to the equations as a hint from nature that the equations of general relativity do not completely describe the conditions at the center of a block hole and that some other physics come into play.

4. Apr 3, 2015

### rootone

Why should electrons be shot outwards avoiding the same fate as other particles which have mass ?

5. Apr 3, 2015

### Khashishi

You must be referring to relativistic jets which may be shooting out from rotating black holes. It's not just electrons; also other particle are accelerated and shot out. Also, most electrons are sucked in to the black hole; only some of them are shot out. You might take a look at this: http://en.wikipedia.org/wiki/Astrophysical_jet#Rotating_black_hole_as_energy_source

6. Apr 3, 2015

### jimmylegss

well it is interesting that only a tiny part of atoms are actual mass, and most of it is empty space with the possibility of finding one or more electrons somewhere in there.

So when everything is squeezed together, I wonder what happens to those electrons. They become bunched together? If a black hole squeezes a bunch of electrons together, do they stay together by the nuclear strong force? Is there a possibility that black holes convert energy (if you can call electrons that?) to mass?

7. Apr 3, 2015

### rootone

There is a lesser state of collapse than a black hole - a neutron star.
In a neutron star the collapse results in electrons combining with protons to make neutrons.
(I think the released nuclear binding forces result in neutrino emission, but I'm not sure if I recall correctly).
Quite possibly a BH briefly passes through this kind of phase while it is forming.

Neutron stars consist mostly of neutrons tightly crammed together with the some free electrons and ionized nucleii at the surface.
The crammed together neutrons may be in the form of strange atomic nucleii, or a kind of neutron fluid.
Models suggest the core might consist of matter which has degenerated still further into a quark soup or something even stranger.

Last edited: Apr 3, 2015
8. Apr 4, 2015

### Staff: Mentor

You don't need a black hole to see what happens to the electrons under those conditions. Force the electrons close enough to the nucleus and the reaction $p^++e^- \rightarrow n^0+\nu^e$ allows the protons and electrons to combine to form neutrons. The result is a tight little ball of neutrons that, although not a black hole, still has an interestingly strong surface gravity. Google for "neutron star" for more.

9. Apr 6, 2015

### stevebd1

The attached image is diagrammatic but you might find it of interest. I put it together a few years ago while looking into neutron stars (the pdf is better quality).

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Last edited: Apr 6, 2015
10. Apr 6, 2015

### jimmylegss

Thanks a lot, interesting stuff.