# Are there galaxy clusters or dark matter halos in the void?

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.

• There are certainly galaxies in voids, so there are virialized dark-matter halos. Probably no actual clusters, though. Nov 28 '21 at 12:31
• @PeterErwin Why galaxies can live in voids theoretically? Nov 28 '21 at 13:01
• In practice any kind. Spirals seem more common in these quiescent environments. Nov 28 '21 at 21:35
• @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.) Nov 30 '21 at 17:54
• @PeterErwin Thank you for your reply. Dec 1 '21 at 2:12