<p>There exists probably about one <a href="http://en.wikipedia.org/wiki/Supermassive_black_hole">supermassive black hole</a> per galaxy, hence about 100 billion ($10^{11}$) in the observable universe.</p>

<p>If we take 1% of the stars ending as a black hole as a very rough order of magnitude estimate, we'll get about 1 billion stellar black holes per galaxy, hence about $10^{20}$ <a href="http://en.wikipedia.org/wiki/Stellar_black_hole">stellar black holes</a> in the observable universe, give or take one order of magnitude.</p>

<p><a href="http://en.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit">Stars of more than about 15 stellar masses</a> (<a href="http://en.wikipedia.org/wiki/Stellar_classification#Class_O">O class stars</a>) will probably end up as black holes. <a href="http://en.wikipedia.org/wiki/Stellar_classification#Harvard_spectral_classification">About 0.00003% of the stars</a> are O-class. The <a href="http://www.asc-csa.gc.ca/eng/educators/resources/astronomy/module2/calculator.asp">lifespan</a> of a star with 15 solar masses is about 11.5 million years. So, we need to multiply the 0.00003% at least by a factor 1000, since the age of the universe is more than 1000-times the life of an O-class star, resulting in 0.03% of all stars over time should have been O-class stars.
(Most stars are red dwarfs, and have a longer life-span than the current age of the universe.) Star formation, especially of heavy stars, in the early universe has probably been <a href="http://www.caltech.edu/content/bursts-star-formation-early-universe">higher than today</a>.
Therefore I'm estimating the number of stellar black holes as about 1% the number of all stars.</p>

<p><a href="http://en.wikipedia.org/wiki/Intermediate-mass_black_hole">Intermediate-mass black holes</a> as presumed centers of <a href="http://en.wikipedia.org/wiki/Globular_cluster">globular clusters</a> are harder to estimate, since there isn't much observational evidence. If the hypotheses turns out to be correct, and we take 1000 globular clusters per galaxy, we get about $10^{14}$ IMBHs.</p>

<p>There is no observational evidence for the existence of small black holes (smaller than a few solar masses).</p>

CC BY-SA 3.0
2014-05-14T14:12:45.583Z
2014-05-14T14:12:45.583Z
Gerald
<p>How many black holes exist and what is their distrubtion over mass?
There is a <a href="http://en.wikipedia.org/wiki/List_of_black_holes" rel="noreferrer">list of black holes</a>, but I'm interested in an estimate of all black holes in the visible universe.</p>

CC BY-SA 3.0
2014-05-14T13:57:13.873Z
Supermassive black holes in particular? Why the supermassive tag?
Blackbody Blacklight
CC BY-SA 3.0
2014-05-14T14:04:50.313Z
@BlackbodyBlacklight no all of them including super-massive ones...
draks ...
<black-hole><supermassive-black-hole>
How many black holes exist?
draks ...
# How many black holes exist?

(Asked by: username_0 on 2014-05-14)

How many black holes exist and what is their distrubtion over mass?
There is a [list of black holes](http://en.wikipedia.org/wiki/List_of_black_holes), but I'm interested in an estimate of all black holes in the visible universe.

**Tags:** black-hole, supermassive-black-hole
> **Comments:**
> **username_1**: Supermassive black holes in particular? Why the supermassive tag?  
> **username_0**: @BlackbodyBlacklight no all of them including super-massive ones...  

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## 1 answers

### Answer by username_2 on 2014-05-14. Score: 8 | Accepted answer

There exists probably about one [supermassive black hole](http://en.wikipedia.org/wiki/Supermassive_black_hole) per galaxy, hence about 100 billion ($10^{11}$) in the observable universe.

If we take 1% of the stars ending as a black hole as a very rough order of magnitude estimate, we'll get about 1 billion stellar black holes per galaxy, hence about $10^{20}$ [stellar black holes](http://en.wikipedia.org/wiki/Stellar_black_hole) in the observable universe, give or take one order of magnitude.

[Stars of more than about 15 stellar masses](http://en.wikipedia.org/wiki/Tolman%E2%80%93Oppenheimer%E2%80%93Volkoff_limit) ([O class stars](http://en.wikipedia.org/wiki/Stellar_classification#Class_O)) will probably end up as black holes. [About 0.00003% of the stars](http://en.wikipedia.org/wiki/Stellar_classification#Harvard_spectral_classification) are O-class. The [lifespan](http://www.asc-csa.gc.ca/eng/educators/resources/astronomy/module2/calculator.asp) of a star with 15 solar masses is about 11.5 million years. So, we need to multiply the 0.00003% at least by a factor 1000, since the age of the universe is more than 1000-times the life of an O-class star, resulting in 0.03% of all stars over time should have been O-class stars.
(Most stars are red dwarfs, and have a longer life-span than the current age of the universe.) Star formation, especially of heavy stars, in the early universe has probably been [higher than today](http://www.caltech.edu/content/bursts-star-formation-early-universe).
Therefore I'm estimating the number of stellar black holes as about 1% the number of all stars.

[Intermediate-mass black holes](http://en.wikipedia.org/wiki/Intermediate-mass_black_hole) as presumed centers of [globular clusters](http://en.wikipedia.org/wiki/Globular_cluster) are harder to estimate, since there isn't much observational evidence. If the hypotheses turns out to be correct, and we take 1000 globular clusters per galaxy, we get about $10^{14}$ IMBHs.

There is no observational evidence for the existence of small black holes (smaller than a few solar masses).


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