<blockquote>
  <p>Does that suggest that about a half of the stars in the observable universe could not belong to any galaxy?</p>
</blockquote>

<p>Not really.  A key sentence in the article is "The best interpretation is that we are seeing light from stars outside of galaxies but in the same dark matter halo".  So the stars are still within the dark matter halo of a galaxy, but are outside the boundary of the galaxy if the dark matter halo is not considered.  </p>

<p>Furthermore the "intrahalo light" explanation is just one of two possible explanations according to <a href="http://arxiv.org/pdf/1601.02514v1.pdf" rel="nofollow">Updated analysis of near-infrared background fluctuations</a> which explains:</p>

<blockquote>
  <p>Two scenarios have been proposed to interpret the clustering excess. The first advocates the contribution from intrahalo light (IHL), i.e. relatively old stars stripped from
  their parent galaxies following merging events. These stars
  therefore reside in between dark matter halos and constitute a low-surface brightness haze around galaxies. The IHL
  is expected to come mostly from low redshifts (1 + z &lt;
  ∼ 1.5)
  systems (Cooray et al. 2012b; Zemcov et al. 2014).  </p>
  
  <p>The second scenario is instead based on the presence
  of a class of early, highly obscured accreting black holes
  of intermediate mass (∼ 10^4−6M⊙) at z >
  ∼ 13 (Yue et al.
  2013b, 2014). As a suitable mechanism to produce such
  objects does exist – the so called Direct Collapse Black
  Holes (DCBH, for a concise overview of the problem see
  Ferrara et al. 2014), and the interpretation of the super-
  massive black holes observed at z = 6 seemingly requires
  massive seeds (Volonteri &amp; Bellovary 2011), such hypothesis seems particularly worth exploring.   </p>
  
  <p>Both scenarios successfully explain the observed clustering excess, albeit with apparently demanding requirements. In fact, if the excess is to be explained by intra-
  halo light, then a large fraction of the stars at low-z must
  reside outside systems that we would normally classify as
  “galaxies” (Zemcov et al. 2014). On the other hand, in the
  DCBH scenario the abundance of seed black holes produced
  until z ∼ 13 must represent a sizeable fraction of the estimated present-day black hole abundance, as deduced from
  local scaling relations (Kormendy &amp; Ho 2013) and recently
  revised by Comastri et al. (2015). However, it is important
  to outline that both scenarios are not in conflict with any
  known observational evidence</p>
</blockquote>

CC BY-SA 3.0
2016-04-01T18:50:26.777Z
2016-04-01T18:57:16.047Z
2016-04-01T18:57:16.047Z
DavePhD
<p>My question is about the implications of the observations recently made by the Cosmic Infrared Background Experiment, or CIBER, from Caltech. I've read at <a href="http://www.caltech.edu/news/caltech-rocket-experiment-finds-surprising-cosmic-light-44399">Caltech web site</a>:</p>

<blockquote>
  <p>"The total light produced by these stray stars is about equal to the background light we get from counting up individual galaxies."</p>
</blockquote>

<p>Does that suggest that about a half of the stars in the observable universe could not belong to any galaxy?</p>

CC BY-SA 4.0
2021-08-04T12:37:14.440Z
I came across your question randomly but noticed you are a user in Spanish SE and also a site moderator elsewhere. Do you have any thoughts on the following in meta? Might a question like this fly in Spanish SE? [Where can I ask “Do they use seasons in Ecuador?”](https://meta.stackexchange.com/q/367114/303080)
uhoh
<galaxy><observational-astronomy><observable-universe>
Does CIBER Experiment from Caltech suggest that there can be lots of stars which are not in any galaxy?
Charo
# Does CIBER Experiment from Caltech suggest that there can be lots of stars which are not in any galaxy?

(Asked by: username_0 on 2015-01-06)

My question is about the implications of the observations recently made by the Cosmic Infrared Background Experiment, or CIBER, from Caltech. I've read at [Caltech web site](http://www.caltech.edu/news/caltech-rocket-experiment-finds-surprising-cosmic-light-44399):

> "The total light produced by these stray stars is about equal to the background light we get from counting up individual galaxies."

Does that suggest that about a half of the stars in the observable universe could not belong to any galaxy?

**Tags:** galaxy, observational-astronomy, observable-universe

> **Comments:**
> **username_1**: I came across your question randomly but noticed you are a user in Spanish SE and also a site moderator elsewhere. Do you have any thoughts on the following in meta? Might a question like this fly in Spanish SE? [Where can I ask “Do they use seasons in Ecuador?”](https://meta.stackexchange.com/q/367114/303080)  

---

## 1 answers

### Answer by username_2 on 2016-04-01. Score: 2

> Does that suggest that about a half of the stars in the observable universe could not belong to any galaxy?

Not really. A key sentence in the article is "The best interpretation is that we are seeing light from stars outside of galaxies but in the same dark matter halo". So the stars are still within the dark matter halo of a galaxy, but are outside the boundary of the galaxy if the dark matter halo is not considered.

Furthermore the "intrahalo light" explanation is just one of two possible explanations according to [Updated analysis of near-infrared background fluctuations](http://arxiv.org/pdf/1601.02514v1.pdf) which explains:

> Two scenarios have been proposed to interpret the clustering excess. The first advocates the contribution from intrahalo light (IHL), i.e. relatively old stars stripped from
> their parent galaxies following merging events. These stars
> therefore reside in between dark matter halos and constitute a low-surface brightness haze around galaxies. The IHL
> is expected to come mostly from low redshifts (1 + z <
> ∼ 1.5)
> systems (Cooray et al. 2012b; Zemcov et al. 2014).
>
> The second scenario is instead based on the presence
> of a class of early, highly obscured accreting black holes
> of intermediate mass (∼ 10^4−6M⊙) at z >
> ∼ 13 (Yue et al.
> 2013b, 2014). As a suitable mechanism to produce such
> objects does exist – the so called Direct Collapse Black
> Holes (DCBH, for a concise overview of the problem see
> Ferrara et al. 2014), and the interpretation of the super-
> massive black holes observed at z = 6 seemingly requires
> massive seeds (Volonteri & Bellovary 2011), such hypothesis seems particularly worth exploring.
>
> Both scenarios successfully explain the observed clustering excess, albeit with apparently demanding requirements. In fact, if the excess is to be explained by intra-
> halo light, then a large fraction of the stars at low-z must
> reside outside systems that we would normally classify as
> “galaxies” (Zemcov et al. 2014). On the other hand, in the
> DCBH scenario the abundance of seed black holes produced
> until z ∼ 13 must represent a sizeable fraction of the estimated present-day black hole abundance, as deduced from
> local scaling relations (Kormendy & Ho 2013) and recently
> revised by Comastri et al. (2015). However, it is important
> to outline that both scenarios are not in conflict with any
> known observational evidence


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