<p>The mass at which a star is able to condense into a black hole upon its death is called the <a href="https://en.m.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit" rel="nofollow noreferrer">Tolman–Oppenheimer–Volkoff Limit</a>, which is roughly 2.17 solar masses. At this mass, the <a href="https://en.wikipedia.org/wiki/Schwarzschild_radius" rel="nofollow noreferrer">Schwarzschild radius</a> of the black hole (the size of its event horizon) is about 6410 meters by the equation </p>

<p><span class="math-container">$$r_s = \frac{2GM}{c^2}.$$</span></p>

<p>EDIT: I'd also like to add that the theoretical minimum mass for a black hole is the Planck mass, <span class="math-container">$2.2\times 10^{−8}$</span> kg, which would yield a radius of <span class="math-container">$3.267\times 10^{-35}$</span> meters, though these would not be formed by stellar collapse, though they could have formed as primordial black holes in the very early universe.</p>

CC BY-SA 4.0
2019-04-19T03:54:19.580Z
Chandrasekhar limit is for white dwarves. Neutron stars can be >2 solar masses.
Mike G
CC BY-SA 4.0
2019-04-19T04:21:45.823Z
nice answer! I added some links and formatted your equation using [MathJax](https://math.meta.stackexchange.com/q/5020/284619), but I wasn't sure how to parse "or 2.8 * 10^3 solar masses" properly. Feel free to edit further.
uhoh
CC BY-SA 4.0
2019-04-19T15:23:23.207Z
@MikeG I disagree, it's the upper limit at which white dwarves can be stable, and it is at this limit that collapse into a condensed body becomes possible. There is a limit, the TOV limit, which is a bit above 2 solar masses, above which "cold" neutron stars are unstable, that may be what you are thinking of?
Adam Tidball
CC BY-SA 4.0
2019-04-19T16:18:09.870Z
Yes. Below the TOV limit, the compact object is not a black hole.
Mike G
CC BY-SA 4.0
2019-04-19T17:22:52.597Z
@MikeG Ok, I see what you mean now, I agree and will edit accordingly
Adam Tidball
CC BY-SA 4.0
2019-04-19T03:13:02.027Z
2019-04-19T17:56:40.837Z
2019-04-19T17:56:40.837Z
Adam Tidball
<p>I was watching the video <a href="https://www.youtube.com/watch?v=h3KOmt9onvc" rel="noreferrer">I Put a 1mm Size Black Hole Next to Earth and This Happened - Universe Sandbox 2</a> discussing what would happen if a 1 millimeter black hole is orbiting the earth, and I began questioning myself, is it really possible to naturally have such a small black hole?</p>

<p>What is the smallest size that a black hole can form naturally in real life?</p>

CC BY-SA 4.0
2019-04-11T01:27:08.203Z
Interesting question! I adjusted your wording a bit, does it still look okay?
uhoh
CC BY-SA 4.0
2019-04-11T01:28:17.303Z
sure... sorry about my poor english jejeje :V
Chico3001
CC BY-SA 4.0
2019-04-11T03:02:04.220Z
De nada, I sure wish I could speak more than one language!
uhoh
CC BY-SA 4.0
2019-04-11T07:30:53.707Z
I assume you’re excluding non-stellar black holes (eg primordial BHs) as we currently have no evidence of their existence. Since the Schwarzschild radius is derived from the mass, the starting point is the minimum stellar mass that can collapse into a black hole....
Chappo Hasn't Forgotten
CC BY-SA 4.0
2019-04-12T03:34:29.203Z
We don't know of any process that could create a 1 mm BH, apart from waiting an extremely long time so that the CMB cools down enough to let regular stellar BHs evaporate by Hawking radiation, and then waiting an insanely long time (over $10^{60}$ years) for such BHs to lose most of their mass.
PM 2Ring
CC BY-SA 4.0
2021-03-09T02:09:38.597Z
It depends what you refer to as "natural".
Gene Raza
<black-hole><size><universe-sandbox>
What is the smallest diameter black hole that can be formed naturally?
Chico3001
# What is the smallest diameter black hole that can be formed naturally?

(Asked by: username_0 on 2019-04-11)

I was watching the video [I Put a 1mm Size Black Hole Next to Earth and This Happened - Universe Sandbox 2](https://www.youtube.com/watch?v=h3KOmt9onvc) discussing what would happen if a 1 millimeter black hole is orbiting the earth, and I began questioning myself, is it really possible to naturally have such a small black hole?

What is the smallest size that a black hole can form naturally in real life?

**Tags:** black-hole, size, universe-sandbox
> **Comments:**
> **username_1**: Interesting question! I adjusted your wording a bit, does it still look okay?  
> **username_0**: sure... sorry about my poor english jejeje :V  
> **username_1**: De nada, I sure wish I could speak more than one language!  
> **username_2**: I assume you’re excluding non-stellar black holes (eg primordial BHs) as we currently have no evidence of their existence. Since the Schwarzschild radius is derived from the mass, the starting point is the minimum stellar mass that can collapse into a black hole....  
> **username_3**: We don't know of any process that could create a 1 mm BH, apart from waiting an extremely long time so that the CMB cools down enough to let regular stellar BHs evaporate by Hawking radiation, and then waiting an insanely long time (over $10^{60}$ years) for such BHs to lose most of their mass.  
> **username_4**: It depends what you refer to as "natural".  

---

## 1 answers

### Answer by username_5 on 2019-04-19. Score: 4 | Accepted answer

The mass at which a star is able to condense into a black hole upon its death is called the [Tolman–Oppenheimer–Volkoff Limit](https://en.m.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit), which is roughly 2.17 solar masses. At this mass, the [Schwarzschild radius](https://en.wikipedia.org/wiki/Schwarzschild_radius) of the black hole (the size of its event horizon) is about 6410 meters by the equation

$$r\_s = \frac{2GM}{c^2}.$$

EDIT: I'd also like to add that the theoretical minimum mass for a black hole is the Planck mass, $2.2\times 10^{−8}$ kg, which would yield a radius of $3.267\times 10^{-35}$ meters, though these would not be formed by stellar collapse, though they could have formed as primordial black holes in the very early universe.

> **Comments:**
> **username_6**: Chandrasekhar limit is for white dwarves. Neutron stars can be >2 solar masses.  
> **username_1**: nice answer! I added some links and formatted your equation using [MathJax](https://math.meta.stackexchange.com/q/5020/284619), but I wasn't sure how to parse "or 2.8 * 10^3 solar masses" properly. Feel free to edit further.  
> **username_5**: @MikeG I disagree, it's the upper limit at which white dwarves can be stable, and it is at this limit that collapse into a condensed body becomes possible. There is a limit, the TOV limit, which is a bit above 2 solar masses, above which "cold" neutron stars are unstable, that may be what you are thinking of?  
> **username_6**: Yes. Below the TOV limit, the compact object is not a black hole.  
> **username_5**: @MikeG Ok, I see what you mean now, I agree and will edit accordingly  

---

