<p>The void usually refers to the region of the Universe where the overdensity <span class="math-container">$\delta(x)$</span> is less than zero. What I'm curious about is whether there are virialized objects, like galaxy clusters or dark matter halos, living in such an underdense environment.</p>

CC BY-SA 4.0
2021-11-28T12:31:34.943Z
There are certainly *galaxies* in voids, so there are virialized dark-matter halos. Probably no actual clusters, though.
Peter Erwin
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2021-11-28T13:01:57.620Z
@PeterErwin Why galaxies can live in voids theoretically?
Wang Yun
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2021-11-28T21:35:35.157Z
In practice any kind. Spirals seem more common in these quiescent environments.
Anders Sandberg
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2021-11-30T17:54:54.717Z
@WangYun A void is where the *average* overdensity is low. There will still be local variations, though, so there can be regions within a void where the local overdensity is large enough for gravitational collapse of a halo to take place. (Such regions will be much less common in a void, of course.)
Peter Erwin
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2021-12-01T02:12:07.833Z
@PeterErwin Thank you for your reply.
Wang Yun
<cosmology><dark-matter><galaxy-cluster>
Are there galaxy clusters or dark matter halos in the void?
Wang Yun
# Are there galaxy clusters or dark matter halos in the void?

(Asked by: username_0 on 2021-11-28)

The void usually refers to the region of the Universe where the overdensity $\delta(x)$ is less than zero. What I'm curious about is whether there are virialized objects, like galaxy clusters or dark matter halos, living in such an underdense environment.

**Tags:** cosmology, dark-matter, galaxy-cluster

> **Comments:**
> **username_1**: There are certainly *galaxies* in voids, so there are virialized dark-matter halos. Probably no actual clusters, though.  
> **username_0**: @username_1 Why galaxies can live in voids theoretically?  
> **username_2**: In practice any kind. Spirals seem more common in these quiescent environments.  
> **username_1**: @username_0 A void is where the *average* overdensity is low. There will still be local variations, though, so there can be regions within a void where the local overdensity is large enough for gravitational collapse of a halo to take place. (Such regions will be much less common in a void, of course.)  
> **username_0**: @username_1 Thank you for your reply.  

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