<p>I think the following is a fair summary. It's based on a fairly old study by <a href="https://arxiv.org/abs/astro-ph/0406095" rel="noreferrer">Fukugita &amp; Peebles (2004)</a> but the numbers are quite reasonable. Your guess about stars dominating is way off. Most of the baryonic mass is in the intergalactic medium. However it's likely that black holes are a very small fraction of the stellar mass. A remaining uncertainty is whether primordial black holes form part of the dark matter.</p>
<p>The plot was produced by Markus Possel.</p>
<p><a href="https://i.sstatic.net/1Gtfz.jpg" rel="noreferrer"><img src="https://i.sstatic.net/1Gtfz.jpg" alt="Inventory of the universe" /></a></p>

CC BY-SA 4.0
2022-03-01T23:57:06.320Z
Nice, thank you! Seems like my intuition is completely thrown off when it comes to things of such a large scale. I also didn't realise the CMBR and neutrino background were such a significant contribution.
YiFan
CC BY-SA 4.0
2022-03-01T23:49:37.537Z
2022-03-01T23:49:37.537Z
ProfRob
<p>The observable matter in the universe is distributed and arranged into various structures, including black holes, stars, nebulae, and the much more diffuse regions of the inter-stellar and inter-galactic mediums.</p>
<blockquote>
<p><strong>Q.</strong> How much observable matter, as a percentage of total mass of observable matter in the universe, is arranged into black holes, stars, nebulae, etc. respectively?</p>
</blockquote>
<p>This seems like a pretty basic question, but Googling has not turned up satisfactory results (instead, it tells me that e.g. observable matter is only 5% of the total mass-energy of the universe, which is not what I asked for).</p>
<p>I would expect that something like 99% of observable matter is trapped within stars, with only &lt;1% being distributed throughout the interstellar medium (e.g. in nebulae). I would also expect that the total amount of mass inside black holes would be orders of magnitude lower than that trapped within stars. Are these estimations actually correct and backed up by evidence?</p>

CC BY-SA 4.0
2022-02-28T02:06:05.260Z
Is "observable matter" all matter apart from dark matter? Eg, does it include particles whose energy is too low to detect directly, like most neutrinos, especially the Cosmic Neutrino Background? BTW, isolated black holes that aren't absorbing matter are very hard to detect, so they aren't any more detectable than dark matter.
PM 2Ring
CC BY-SA 4.0
2022-02-28T02:14:38.317Z
@PM2Ring Good question, one that I hadn't thought of. I was indeed using "observable matter" to refer to any matter except dark matter, but I see there might be an issue. On your second point, I would think that, even if individual black holes without accretion disks are hard to detect, there might be methods to come up with estimates about their overall density in the universe? Though I may be wrong about this.
YiFan
CC BY-SA 4.0
2022-02-28T02:19:33.770Z
Yes, we can estimate black hole numbers, from models of star formation. Not many stars form black holes, and the life span of those stars is relatively short.
PM 2Ring
CC BY-SA 4.0
2022-02-28T02:21:56.467Z
IIRC, despite it's extremely low density, there's quite a lot of matter in the IGM (intergalactic medium). I'm sure we have a good answer about that, but I can't find it. (Maybe it's on Physics.SE).
PM 2Ring
CC BY-SA 4.0
2022-03-01T21:54:31.747Z
Please specify a full list of what is included in "etc " 100% of observable matter is in the form of something observable! Or is it that you want a list of the individual contributions?
ProfRob
CC BY-SA 4.0
2022-03-01T23:35:46.953Z
@ProfRob Yes, what I want is a list of the individual contributions. For example it might be something like: "Stars (98.0%), interstellar/intergalactic medium (1.9%), black holes (0.05%), ..." Of course, there may potentially be contributions from sources I've missed out like mentioned by PM 2Ring above.
YiFan
CC BY-SA 4.0
2022-03-01T23:46:19.353Z
I've edited the question slightly, hopefully that makes it clearer now!
YiFan
CC BY-SA 4.0
2022-03-02T19:52:50.423Z
+1 for asking a question that I didn't know I wanted the answer to, and that actually has an estimated answer.
Mark Foskey
<star><observational-astronomy><cosmology><observable-universe><matter>
How is observable matter distributed in the universe?
YiFan
# How is observable matter distributed in the universe?

(Asked by: username_0 on 2022-02-28)

The observable matter in the universe is distributed and arranged into various structures, including black holes, stars, nebulae, and the much more diffuse regions of the inter-stellar and inter-galactic mediums.

> **Q.** How much observable matter, as a percentage of total mass of observable matter in the universe, is arranged into black holes, stars, nebulae, etc. respectively?

This seems like a pretty basic question, but Googling has not turned up satisfactory results (instead, it tells me that e.g. observable matter is only 5% of the total mass-energy of the universe, which is not what I asked for).

I would expect that something like 99% of observable matter is trapped within stars, with only <1% being distributed throughout the interstellar medium (e.g. in nebulae). I would also expect that the total amount of mass inside black holes would be orders of magnitude lower than that trapped within stars. Are these estimations actually correct and backed up by evidence?

**Tags:** star, observational-astronomy, cosmology, observable-universe, matter

> **Comments:**
> **username_1**: Is "observable matter" all matter apart from dark matter? Eg, does it include particles whose energy is too low to detect directly, like most neutrinos, especially the Cosmic Neutrino Background? BTW, isolated black holes that aren't absorbing matter are very hard to detect, so they aren't any more detectable than dark matter.  
> **username_0**: @username_1 Good question, one that I hadn't thought of. I was indeed using "observable matter" to refer to any matter except dark matter, but I see there might be an issue. On your second point, I would think that, even if individual black holes without accretion disks are hard to detect, there might be methods to come up with estimates about their overall density in the universe? Though I may be wrong about this.  
> **username_1**: Yes, we can estimate black hole numbers, from models of star formation. Not many stars form black holes, and the life span of those stars is relatively short.  
> **username_1**: IIRC, despite it's extremely low density, there's quite a lot of matter in the IGM (intergalactic medium). I'm sure we have a good answer about that, but I can't find it. (Maybe it's on Physics.SE).  
> **username_2**: Please specify a full list of what is included in "etc " 100% of observable matter is in the form of something observable! Or is it that you want a list of the individual contributions?  
> **username_0**: @username_2 Yes, what I want is a list of the individual contributions. For example it might be something like: "Stars (98.0%), interstellar/intergalactic medium (1.9%), black holes (0.05%), ..." Of course, there may potentially be contributions from sources I've missed out like mentioned by PM username_1 above.  
> **username_0**: I've edited the question slightly, hopefully that makes it clearer now!  
> **username_3**: +1 for asking a question that I didn't know I wanted the answer to, and that actually has an estimated answer.  

---

## 1 answers

### Answer by username_2 on 2022-03-01. Score: 9 | Accepted answer

I think the following is a fair summary. It's based on a fairly old study by [Fukugita & Peebles (2004)](https://arxiv.org/abs/astro-ph/0406095) but the numbers are quite reasonable. Your guess about stars dominating is way off. Most of the baryonic mass is in the intergalactic medium. However it's likely that black holes are a very small fraction of the stellar mass. A remaining uncertainty is whether primordial black holes form part of the dark matter.

The plot was produced by Markus Possel.

[![Inventory of the universe](https://i.sstatic.net/1Gtfz.jpg)](https://i.sstatic.net/1Gtfz.jpg)

> **Comments:**
> **username_0**: Nice, thank you! Seems like my intuition is completely thrown off when it comes to things of such a large scale. I also didn't realise the CMBR and neutrino background were such a significant contribution.  

---

