# Tag Info

17

Yes there are. They are mainly based on what dominates the energy density of the universe at the time and they are known as epochs. Thus we have the inflationary epoch in the first tiny fraction ($\sim 10^{-32}$) of a second, when the energy density was dominated by an inflationary field. Then we are in the electroweak epoch, when the weak nuclear and ...

10

This is a tricky science result to explain and, as often turns out to be the case, not quite as secure or solid as the press release recyclers report. The original paper is by Lauer et al. (2021) and measures the cosmic optical background (COB) using images taken with New Horizons, which is way beyond the orbit of Pluto. The advantage over things like HST is ...

30

Dark matter galaxies are possible but very speculative. On a theoretical level, they are hard to form because dark matter interacts only gravitationally (see Anders Sandberg's answer), which makes it hard to lose energy and become bound structures. On an observational level, they would be hard to detect. Gravitational lensing can do something, but since one ...

4

Gravitational lensing observations suggest that there is a large mass of dark matter on either side of the bullet cluster, which is actually one of the major pieces of evidence that dark matter does indeed exist. This dark matter essentially "left behind" the majority of the normal matter in the galaxies it was with as two galaxy clusters collided ...

27

Probably not. Dark matter should really be called "transparent matter" since it does not interact with light. This has an important consequence: it is hard for dark matter - whatever it is - to lose energy by radiating. This is why normal matter can form clouds that accrete into dense regions that in turn become galaxies and stars: energy is ...

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