[Lewis Thomson (OP)]

David has written in with this question to find answers to.

"Is it possible Black Holes could be made from sub-atomic particles?"

Discuss in the comments below...

[Eternal Student]

Hi.

   Is David joining us as a member on the forum?   You could use a false name etc.   Anyway if you aren't, then your answer will be be available in a podcast shortly.   If you are joining us then please say something here and we'll have a discussion.

Best Wishes.

[Kryptid]

The composition of black holes is unknown and possibly unknowable (given how event horizons are). The best we have right now are models that make predictions about how the interior of black holes behave. General relativity gives us a good idea about that, and it says that no known form of matter is stable under the conditions in a black hole. Even subatomic particles lose their individual identity and are crushed into a singularity at the black hole's center. However, that's probably not the whole story.

We currently lack a complete, working theory of quantum gravity. Once we get that, our picture of the interior of black holes may change. So it may turn out that subatomic particles of some kind, perhaps of a type not yet seen, are in the interior of black holes. Or it may turn out that "true" black holes as described by relativity don't really exist and something nearly indistinguishable is created instead. Theories about such objects already exist. Fuzzballs and Magnetospheric Eternally Collapsing Objects are two such alternatives.

[geordief]

I have read that black holes might be viewed not as objects at all but  as extreme spacetime  curvature 

Is that correct or have I perhaps  misconstrued?

[evan_au]

What is a black hole formed from?

Most of the black holes formed today come from the collapse of the core of a star.
- The temperature of a star is so high that electrons are separated from the nucleus of an atom, forming a plasma
- Since electrons & nuclei are "sub-atomic", you could say that black holes are formed from sub-atomic particles.
- As the core of the star collapses, many of the protons and electrons are converted to neutrons (a sub-atomic particle), releasing a burst of neutrinos (which mostly escape). I vaguely recall that around 90% of the energy released in a supernova is in the form of neutrinos.

There is some speculation from cosmologists that, during the early stages of the Big Bang, some black holes may have formed even before protons, electrons and neutrons were  formed. Atoms can't exist at these extreme energy levels, so you might call these "pre-atomic" particles(?)
- Cosmologists think that some of these relic black holes may still exist today

black holes might be viewed not as objects at all but  as extreme spacetime  curvature

Once a black hole has formed, the extreme curvature of spacetime effectively pinches off the singularity from the view of those outside the event horizon.
- At this stage, the only thing you know about the black hole is its mass, spin, and electrical charge.
- At this point, it really doesn't matter what the black hole formed from, because that is not detectable from outside.

[wolfekeeper]

I personally don't think there's anything in a Black Hole. I favour the 'Firewall model' of black holes where all the mass of a black hole is concentrated at the event horizon. My logic is that quantum mechanics means that everything moves as a wave, but the wave function should be effectively zero at an event horizon, so everything will bounce off and hang around just outside, and in fact I think that the horizon can't completely form, but it can get arbitrarily close to forming, there's very, very little mass within where the classical event horizon would be. But I freely admit this is just my opinion.

[geordief]

At this point, it really doesn't matter what the black hole formed from, because that is not detectable from outside

Have heard that said before.Would there be no way to guess (correctly) what a black hole is formed from ...and any way to know if we were correct(and make use of the seemingly correct  knowledge)?

[evan_au]

...the 'Firewall model' of black holes where all the mass of a black hole is concentrated at the event horizon

Let's take the scenario where a neutron star draws more and more material from an orbiting star onto its surface - until it collapses into a black hole perhaps 10miles across.

Within that 5 mile radius of the event horizon, there would already have been a considerable amount of matter while it was still a neutron star. So that can't really still be stuck on the event horizon.

If it were possible to observe the formation of the black hole (eg with a neutrino telescope), the core of the neutron star might be creeping inwards, just a micrometer from the event horizon - but the event horizon would be bounding outwards by yards and miles. So that material would no longer be stuck on the event horizon (from the viewpoint of a distant observer).
https://en.wikipedia.org/wiki/Neutron_star#X-ray_binaries

[Eternal Student]

Hi.

    There's been some reasonable replies but many of them are focusing on what is at the centre of a black hole and I've got to ask why?
    By convention "a Black Hole" is the region of spacetime bound by the Event horizon (EH), usually including the EH itself.
So most of a black hole is just nothing, no material of any kind,  it's just a region of space and time.
   As @evan_au suggested, if there is some matter at what we'll call the centre of the black hole then it has retreated well inside the Event Horizon and by our very best theores it is either:
   (a)   An extremely dense material, occupying a small portion of the region inside the EH.      OR,
   (b)   A genuine singularity,  a point of infinite density.

In either case, most of a black hole is not this stuff.  Most of it is just the spacetime bounded by the EH.

The original question was:

Is it possible Black Holes could be made from sub-atomic particles?

   A reasonable answer is:   No,  most of it is nothing, no material of any kind.
That may change if we discover that gravity can be modelled with force carrying particles,  e.g. we develop a good quantum theory of gravity - but at the moment that is the best answer we can give (I should think).   
    The Scwarzschild solution of the Einstein Field Equations is our best approximation to describe what a black hole is and in that solution,  the region of spacetime we call "the black hole" is a vaccum.   To phrase this another way, a Black hole is not a solid thing of any type, it is just a region of spacetime with extreme spacetime curvature.   The bit of it that might be some material is likely to be so small we can ignore it.
   However, if you (David) were asking what the core or central part of a black hole is made of, then you've already got some answers and replies that are reasonable.

Best Wishes.

[wolfekeeper]

...the 'Firewall model' of black holes where all the mass of a black hole is concentrated at the event horizon

Let's take the scenario where a neutron star draws more and more material from an orbiting star onto its surface - until it collapses into a black hole perhaps 10miles across.

Within that 5 mile radius of the event horizon, there would already have been a considerable amount of matter while it was still a neutron star. So that can't really still be stuck on the event horizon.

If it were possible to observe the formation of the black hole (eg with a neutrino telescope), the core of the neutron star might be creeping inwards, just a micrometer from the event horizon - but the event horizon would be bounding outwards by yards and miles. So that material would no longer be stuck on the event horizon (from the viewpoint of a distant observer).
https://en.wikipedia.org/wiki/Neutron_star#X-ray_binaries

That bothered me for quite a while, but I think there's a snow plow effect. As the event horizon tries to form in the first place any matter inside gets expelled.

[evan_au]

As the event horizon tries to form in the first place any matter inside gets expelled.

This statement seems to imply that gravitation gets reversed during the formation of a black hole. That seems to violate everything we know about gravitation (without actually having a validated theory of quantum gravity).

As I understand it, gravitation always attracts and never repels. The material on a 1-way trajectory towards the center of a black hole doesn't suddenly reverse direction (I exclude elliptical orbits that do not intersect the event horizon).

Part of the problem is that different frames of reference will see different things as a test particle approaches an event horizon of radius (say) 10km:
- From the frame of reference of a test particle approaching the singularity: It will speed up to a significant fraction of c, and pass the the 10km radius in a short time, without experiencing anything special.
- From the frame of reference of a distant observer: A test particle approaching the singularity will speed up to a significant fraction of c, but will continue to emit severely red-shifted photons from just outside the 10km event horizon, for (potentially) a long time.
- However, while an event horizon is growing, my guess is that any photons emitted from an infalling particle will find themselves inside the new event horizon, and will not reach a distant observer.

[wolfekeeper]

The literature says that there is a wave effect that excludes things from the event horizon- particles bounce off. Think of it a bit like super charged refraction, or unmatched transmission line terminations causing reflections.

If you think of it in terms of Feynman quantum particles, summing over all the possible paths, a path that crosses the event horizon will basically not return so doesn't contribute to the wavefunction just outside the event horizon, whereas ones that stay outside can reinforce the ones outside heading away from the event horizon.

The argument that the event horizon is not special is a purely classical argument, and pays no attention to QM. But nature seems to primarily follow QM.

[Eternal Student]

Hi.

The literature says that there is a wave effect that excludes things from the event horizon- particles bounce off.

    I'm not familiar with that literature.   Is there a reference (preferably available online but I could get to a library in a few days).

Best Wishes.

[CatherineMaguire]

I have read that black holes might be viewed not as objects at all but  as extreme spacetime  curvature 

Is that correct or have I perhaps  misconstrued?

You're not the only one who has heard smth like this. I studied this theory at the school, too, so it has been known for some good years