<p>Black holes are not made of anything... at least nothing in our current understanding of reality.</p>
<p>We understand black holes in terms of General Relativity, the theory of gravity.  In this theory there are some &quot;vacuum solutions&quot;  These are solutions that have no matter at any point in spacetime.  One solution is &quot;flat space&quot;, but another solution is a solution with a singularity in time and space.  This solution was discovered by Schwatzchild, and for long was thought to be a mathematical curiosity but not physically real.</p>
<p>But it was later discovered that when a star collapses under gravity it reaches this state.  All the matter falls towards the singularity and we can't describe what happens later than the singularity in time. From the outside it seems as if all the mass of the star is concentrated at one point, but there is actually nothing inside, just the distorted spacetime.</p>
<p>In General relativity nothing can exist in a black hole. For anything falling beyond the event horizon, all directions lead to the singularity.  It is as unavoidable as &quot;next Wednesday&quot;. No ball of matter could exist. In normal space, two particles can remain separate. Inside a black hole this isn't possible, since both particles end up at the singularity in a finite (and short) amount of time.</p>
<p>Now we aren't certain if this truly describes reality, because we lack a theory of gravity that takes account of quantum mechanics. It might be that the singularity is real. It might be that something happens (with strings or something) that prevents the ultimate collapse to a singularity. Whatever it would be outside our current models of reality.  Not &quot;quarks&quot;.</p>

CC BY-SA 4.0
2021-03-27T16:32:14.827Z
Thank you. I always had the interpretation that singularities were a mathematical construct with no physical reality (not unlike a baseball diamond of size 400 square units, that has a side of 20 units, the other root of 400 being -20 but there is no physical distance of -20 other than the vector), and black holes were simply objects with an escape velocity above 300k km/s, neutron stars already reaching half of that.
Mark Besser
CC BY-SA 4.0
2021-03-27T16:38:51.803Z
A key fact about the interior of black holes is that spacial dimensions become "time-like"  You have to go forward in time, you can't go back.  Inside a black hole, you have to go forwards in space. There is no "backwards" or "away from the singularity"  If something string-like happens to prevent ultimate collapse, then the final object would be very very small, probably much smaller than a single proton. We know enough about matter at larger scales and how gravity works to rule out any form of matter that we currently understand well.
James K
CC BY-SA 4.0
2022-07-26T16:09:20.003Z
The “from the outside it seems as if all the mass of the star is concentrated at one point” thing is misleading, Appearance of a black hole is highly symmetric (namely, a hole without angular momentum is spherically symmetric), but no reliable implications on where does “all the mass is concentrated” can be made of that. The gravity of any spherically symmetric (movement included) body is Schwarzschildean, right? m
Incnis Mrsi
CC BY-SA 4.0
2022-07-26T16:51:48.630Z
The “it seems as if all the mass of the star is concentrated at one point” thing is misleading, Outside appearance of a black hole is highly symmetric (namely, a hole without angular momentum is spherically symmetric), but no reliable implication on where does “all the mass is concentrated” ensues. The gravity of any spherically symmetric (movement included) body is Schwarzschildean, right? Moreover, spacetime of a hole resulting from collapse is different from ideal models (Schwarzschild, Kerr etc., having *two* event horizons, both future and past), and the former isn’t “vacuum” everywhere.
Incnis Mrsi
CC BY-SA 4.0
2021-03-26T15:38:50.033Z
2021-03-26T15:38:50.033Z
James K
<p>The structure of black holes is currently unknown,depending largely on the theory of quantum gravity - therefore, your question is not currently answerable</p>

CC BY-SA 4.0
2024-08-11T07:03:47.923Z
2024-08-11T07:03:47.923Z
Harrychink
<p>Can stellar black holes be a category, or subset, of quark stars?</p>
<p><a href="https://i.sstatic.net/QpE2v.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/QpE2v.jpg" alt="
" /></a></p>
<blockquote>
<p>Strange stars are so called not because they're weird (though they
are) but because the extraordinary pressures within them should turn
some of their constituent quarks into a heavy type of quark named
&quot;strange.&quot; Neutrons and protons are made of two lighter types called
&quot;up&quot; and &quot;down.&quot; (The names were chosen whimsically and have no
particular meaning.)</p>
<p>&quot;It's possible that all the stars we have been calling neutron stars
are in fact strange stars&quot; or hybrids of the two, said Turner. If
strange matter does convert everything it touches into more strange
matter, these stars would consist of the stuff right up to their
perfectly hard-edged surfaces, with nothing but vacuum above. If it
doesn't, the stars could be hybrids with strange-matter cores and
neutron-star outer layers.</p>
<p><em><em>from</em> <a href="https://skyandtelescope.org/astronomy-news/quark-matter-stars-said-found/" rel="nofollow noreferrer">https://skyandtelescope.org/astronomy-news/quark-matter-stars-said-found/</a></em></p>
</blockquote>
<p>The visible quark stars such as the one depicted would be quark-neutron hybrids. This would conveniently answer the question &quot;what is black hole substance made of&quot;.</p>
<p>If this is certain to not be the case, what (if any) known substance can black holes de made of?</p>
<p>Note, I said a <em>subset</em> - &quot;...strange stars exhibit a low-luminosity but high-temperature bremsstrahlung spectrum, which, in combination with the emission properties of the accretion disc, may be the key signature to differentiate massive strange stars from the black hole.&quot; in <a href="https://academic.oup.com/mnras/article/400/3/1632/962273" rel="nofollow noreferrer">https://academic.oup.com/mnras/article/400/3/1632/962273</a></p>
<p><a href="https://physicsworld.com/a/calculations-point-to-massive-quark-stars/" rel="nofollow noreferrer">https://physicsworld.com/a/calculations-point-to-massive-quark-stars/</a></p>

CC BY-SA 4.0
2021-03-26T04:55:49.720Z
Should read these answers. https://astronomy.stackexchange.com/questions/2441/does-matter-accumulate-just-outside-the-event-horizon-of-a-black-hole?rq=1
James K
CC BY-SA 4.0
2021-03-26T12:17:24.940Z
@JamesK Thank you, I did, great post. Here's the thing. Black holes are made of something, surely. What's smaller than neutrons? Quarks. Thus, perhaps black hole matter may be a subset of pure quark star material.
Mark Besser
<black-hole>
Can black holes be a subset of quark stars? If not, what are black holes made of?
Mark Besser
# Can black holes be a subset of quark stars? If not, what are black holes made of?

(Asked by: username_0 on 2021-03-25)

Can stellar black holes be a category, or subset, of quark stars?

[![
](https://i.sstatic.net/QpE2v.jpg)](https://i.sstatic.net/QpE2v.jpg)

> Strange stars are so called not because they're weird (though they
> are) but because the extraordinary pressures within them should turn
> some of their constituent quarks into a heavy type of quark named
> "strange." Neutrons and protons are made of two lighter types called
> "up" and "down." (The names were chosen whimsically and have no
> particular meaning.)
>
> "It's possible that all the stars we have been calling neutron stars
> are in fact strange stars" or hybrids of the two, said Turner. If
> strange matter does convert everything it touches into more strange
> matter, these stars would consist of the stuff right up to their
> perfectly hard-edged surfaces, with nothing but vacuum above. If it
> doesn't, the stars could be hybrids with strange-matter cores and
> neutron-star outer layers.
>
> **from* <https://skyandtelescope.org/astronomy-news/quark-matter-stars-said-found/>*

The visible quark stars such as the one depicted would be quark-neutron hybrids. This would conveniently answer the question "what is black hole substance made of".

If this is certain to not be the case, what (if any) known substance can black holes de made of?

Note, I said a *subset* - "...strange stars exhibit a low-luminosity but high-temperature bremsstrahlung spectrum, which, in combination with the emission properties of the accretion disc, may be the key signature to differentiate massive strange stars from the black hole." in <https://academic.oup.com/mnras/article/400/3/1632/962273>

<https://physicsworld.com/a/calculations-point-to-massive-quark-stars/>

**Tags:** black-hole

> **Comments:**
> **username_1**: Should read these answers. https://astronomy.stackexchange.com/questions/2441/does-matter-accumulate-just-outside-the-event-horizon-of-a-black-hole?rq=1  
> **username_0**: @JamesK Thank you, I did, great post. Here's the thing. Black holes are made of something, surely. What's smaller than neutrons? Quarks. Thus, perhaps black hole matter may be a subset of pure quark star material.  

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## 2 answers

### Answer by username_1 on 2021-03-26. Score: 3 | Accepted answer

Black holes are not made of anything... at least nothing in our current understanding of reality.

We understand black holes in terms of General Relativity, the theory of gravity. In this theory there are some "vacuum solutions" These are solutions that have no matter at any point in spacetime. One solution is "flat space", but another solution is a solution with a singularity in time and space. This solution was discovered by Schwatzchild, and for long was thought to be a mathematical curiosity but not physically real.

But it was later discovered that when a star collapses under gravity it reaches this state. All the matter falls towards the singularity and we can't describe what happens later than the singularity in time. From the outside it seems as if all the mass of the star is concentrated at one point, but there is actually nothing inside, just the distorted spacetime.

In General relativity nothing can exist in a black hole. For anything falling beyond the event horizon, all directions lead to the singularity. It is as unavoidable as "next Wednesday". No ball of matter could exist. In normal space, two particles can remain separate. Inside a black hole this isn't possible, since both particles end up at the singularity in a finite (and short) amount of time.

Now we aren't certain if this truly describes reality, because we lack a theory of gravity that takes account of quantum mechanics. It might be that the singularity is real. It might be that something happens (with strings or something) that prevents the ultimate collapse to a singularity. Whatever it would be outside our current models of reality. Not "quarks".

> **Comments:**
> **username_0**: Thank you. I always had the interpretation that singularities were a mathematical construct with no physical reality (not unlike a baseball diamond of size 400 square units, that has a side of 20 units, the other root of 400 being -20 but there is no physical distance of -20 other than the vector), and black holes were simply objects with an escape velocity above 300k km/s, neutron stars already reaching half of that.  
> **username_1**: A key fact about the interior of black holes is that spacial dimensions become "time-like"  You have to go forward in time, you can't go back.  Inside a black hole, you have to go forwards in space. There is no "backwards" or "away from the singularity"  If something string-like happens to prevent ultimate collapse, then the final object would be very very small, probably much smaller than a single proton. We know enough about matter at larger scales and how gravity works to rule out any form of matter that we currently understand well.  
> **username_2**: The “from the outside it seems as if all the mass of the star is concentrated at one point” thing is misleading, Appearance of a black hole is highly symmetric (namely, a hole without angular momentum is spherically symmetric), but no reliable implications on where does “all the mass is concentrated” can be made of that. The gravity of any spherically symmetric (movement included) body is Schwarzschildean, right? m  
> **username_2**: The “it seems as if all the mass of the star is concentrated at one point” thing is misleading, Outside appearance of a black hole is highly symmetric (namely, a hole without angular momentum is spherically symmetric), but no reliable implication on where does “all the mass is concentrated” ensues. The gravity of any spherically symmetric (movement included) body is Schwarzschildean, right? Moreover, spacetime of a hole resulting from collapse is different from ideal models (Schwarzschild, Kerr etc., having *two* event horizons, both future and past), and the former isn’t “vacuum” everywhere.  

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### Answer by username_3 on 2024-08-11. Score: 0

The structure of black holes is currently unknown,depending largely on the theory of quantum gravity - therefore, your question is not currently answerable


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