<p>According to quite recent research the observable universe contains about 2 trillion galaxies (<span class="math-container">$2 \cdot 10^{12}$</span>). But what is counted there? Does this number also contain dwarf galaxies? According to wiki about 10 times more than normal galaxies exist. But is there a hard gap in between normal and dwarf galaxies?</p>
<p>To resolve all those questions does exist a chart or diagram similar to this?</p>
<div class="s-table-container">
<table class="s-table">
<thead>
<tr>
<th>Number of Stars</th>
<th>Count</th>
</tr>
</thead>
<tbody>
<tr>
<td><span class="math-container">$&lt; 10^6$</span></td>
<td><span class="math-container">$10^{11}$</span></td>
</tr>
<tr>
<td><span class="math-container">$10^6 - 10^7$</span></td>
<td><span class="math-container">$10^{10}$</span></td>
</tr>
<tr>
<td><span class="math-container">$10^7 - 10^8$</span></td>
<td><span class="math-container">$10^{9}$</span></td>
</tr>
<tr>
<td>...</td>
<td>...</td>
</tr>
</tbody>
</table>
</div><hr />
<p>bonus question:</p>
<p>As far as I know we are able to see new, more distant galaxies in the next millions of years. Due to the further expansion of the universe and the acceleration there will be some point were the light of some galaxies can't reach us anymore (hubble radius) and we can see less and less galaxies again. So the number of galaxies we can see is not a constant (also some get extinct or new are created). Is there some research about the max number of galaxies we are ever able to see. Would be it much different to the 2 trillion now?</p>

CC BY-SA 4.0
2021-03-22T22:39:52.770Z
[This](https://astronomy.stackexchange.com/questions/16132/boötes-void-numbers-2016/16146#16146) and [this](https://astronomy.stackexchange.com/questions/8903/how-many-galaxies-are-there-in-the-hercules-corona-borealis-great-wall) previous answers calculated the number of galaxies by size in two different volumes. You could use that approach the get your answer, just using the total volume of the observable Universe instead (which is 4π/3 R³, where the radius R is roughly 46 billion lightyears).
pela
CC BY-SA 4.0
2021-03-23T01:23:14.007Z
different but related: [Does the recent news of “ten times more galaxies” imply that there is correspondingly less dark matter?](https://astronomy.stackexchange.com/q/18708/7982)
uhoh
CC BY-SA 4.0
2021-03-23T02:08:52.857Z
@pela using the numbers in that link (SMC as lower bound) the result would be 1.87*10^12. That would be very close to the 2 trillion mentioned above. But is it correct? The plot has y-units of h^3 MPc^-3 but in text you are using h^-3 instead. Which one would be correct? Using h^3 would result in 1.6*10^13 galaxies greater than SMC. .....The linked [plot creator](https://hmf.icrar.org) also has many more interesting relations. Thank you for that as well!
J. Doe
CC BY-SA 4.0
2021-03-23T21:54:55.707Z
@J.Doe Thanks for spotting that, there was a typo. Distances are (in some cases) measured in $h^{-1}\,\mathrm{Mpc}$, in which case densities will be measured in $h^{3}\,\mathrm{Mpc}^{-3}$. In the calculation I used the correct value, but the text was wrong.
pela
CC BY-SA 4.0
2021-03-24T00:39:11.100Z
@pela Oh, I mixed it up in computation. So the correct result will be about 1.87*10^12 galaxies in the observable universe which are at least as massive as the SMC (about 7*10^9 solar masses). But to be correct that doesn't need to be the numbers of stars. The star size can vary. Galaxies also have a massive center. E.g. wiki quote SMC: 'several hundred million stars, and has a total mass of approximately 7 billion solar masses' ... it only has hundred million stars but 7 billion solar masses. So the real number of stars is much smaller.
J. Doe
CC BY-SA 4.0
2021-03-29T22:08:01.913Z
Yes, stars come in a distribution of sizes, from roughly 0.1 to 100 Solar masses, but with a steep decrease in number with mass, such that the average is around 0.3 Solar masses (depending on the “initial mass function”, and the age of the stellar population). But stars are not the only constituents of the galaxy, there may be as much gas, and ten times as much dark matter.
pela
<galaxy><expansion><observable-universe><hubble-constant>
How many galaxies are predicted in the observable universe? Does it contain dwarfs? Is there any size-ratio diagram?
J. Doe
# How many galaxies are predicted in the observable universe? Does it contain dwarfs? Is there any size-ratio diagram?

(Asked by: username_0 on 2021-03-22)

According to quite recent research the observable universe contains about 2 trillion galaxies ($2 \cdot 10^{12}$). But what is counted there? Does this number also contain dwarf galaxies? According to wiki about 10 times more than normal galaxies exist. But is there a hard gap in between normal and dwarf galaxies?

To resolve all those questions does exist a chart or diagram similar to this?

| Number of Stars | Count |
| --- | --- |
| $< 10^6$ | $10^{11}$ |
| $10^6 - 10^7$ | $10^{10}$ |
| $10^7 - 10^8$ | $10^{9}$ |
| ... | ... |

---

bonus question:

As far as I know we are able to see new, more distant galaxies in the next millions of years. Due to the further expansion of the universe and the acceleration there will be some point were the light of some galaxies can't reach us anymore (hubble radius) and we can see less and less galaxies again. So the number of galaxies we can see is not a constant (also some get extinct or new are created). Is there some research about the max number of galaxies we are ever able to see. Would be it much different to the 2 trillion now?

**Tags:** galaxy, expansion, observable-universe, hubble-constant

> **Comments:**
> **username_1**: [This](https://astronomy.stackexchange.com/questions/16132/boötes-void-numbers-2016/16146#16146) and [this](https://astronomy.stackexchange.com/questions/8903/how-many-galaxies-are-there-in-the-hercules-corona-borealis-great-wall) previous answers calculated the number of galaxies by size in two different volumes. You could use that approach the get your answer, just using the total volume of the observable Universe instead (which is 4π/3 R³, where the radius R is roughly 46 billion lightyears).  
> **username_2**: different but related: [Does the recent news of “ten times more galaxies” imply that there is correspondingly less dark matter?](https://astronomy.stackexchange.com/q/18708/7982)  
> **username_0**: @username_1 using the numbers in that link (SMC as lower bound) the result would be 1.87*10^12. That would be very close to the 2 trillion mentioned above. But is it correct? The plot has y-units of h^3 MPc^-3 but in text you are using h^-3 instead. Which one would be correct? Using h^3 would result in 1.6*10^13 galaxies greater than SMC. .....The linked [plot creator](https://hmf.icrar.org) also has many more interesting relations. Thank you for that as well!  
> **username_1**: @J.Doe Thanks for spotting that, there was a typo. Distances are (in some cases) measured in $h^{-1}\,\mathrm{Mpc}$, in which case densities will be measured in $h^{3}\,\mathrm{Mpc}^{-3}$. In the calculation I used the correct value, but the text was wrong.  
> **username_0**: @username_1 Oh, I mixed it up in computation. So the correct result will be about 1.87*10^12 galaxies in the observable universe which are at least as massive as the SMC (about 7*10^9 solar masses). But to be correct that doesn't need to be the numbers of stars. The star size can vary. Galaxies also have a massive center. E.g. wiki quote SMC: 'several hundred million stars, and has a total mass of approximately 7 billion solar masses' ... it only has hundred million stars but 7 billion solar masses. So the real number of stars is much smaller.  
> **username_1**: Yes, stars come in a distribution of sizes, from roughly 0.1 to 100 Solar masses, but with a steep decrease in number with mass, such that the average is around 0.3 Solar masses (depending on the “initial mass function”, and the age of the stellar population). But stars are not the only constituents of the galaxy, there may be as much gas, and ten times as much dark matter.  

---

## 0 answers

