What it seems like is most likely is that dark matter is going to turn out to not be some mysterious unobtanium new physics substance, but rather likely just things which aren’t very bright — dust and rocks and rogue planets and gas and such... stuff that is hard to see and therefore hard to account for in our galaxy formation models.
If gravity is simply the curving of space caused by matter, why must there be 'dark matter'? Why cant there be something else that bends space? Or who says space is homogeneous and flat-why cant there be 'bubbles' of positively and 'negatively' curved space? If the universe is expanding, why would it expand homogeneously in all directions? After all, isn't the cosmic microwave background anisotropic?
> It's called "dark" because no one knows what it is.
It's called "dark" because we can't see it, except for the gravitational effects it has on visible matter.
Neutrinos hardly interact at all with normal matter, as such it is a form of dark matter called hot dark matter[1].
However based on measurements we've ruled out[2] neutrinos as the main source of dark matter, hence we're looking for something else.
Since the only clue we have so far is the gravitational effect, it is possible that the solution is to modify the theory of gravity instead of finding new particles. People are looking into this as well. And heck, maybe it's both. Time will tell!
Only conventional left-handed neutrinos are ruled out as significant HDM.
It is rarely mentioned amongst all the Higgs back-slapping, that the Standard Model does not yet have a complete and verified theory of neutrino physics: masses? Majorana/Dirac? self-anti-particle? chiralities? ...
There may be right-handed neutrinos that do not interact via the weak force (which is maximally parity-violating). They would only interact gravitationally and play a role dark matter:
I mean, it's conceivable that there could be some unknown thing that curves space in oddly specific ways that look just like matter, and also kind of moves in bulk like matter, but that would be drastically crazier than even dark matter is, so no one should expect it to be more likely.
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[ 2.2 ms ] story [ 22.4 ms ] threadhttps://en.wikipedia.org/wiki/Dark_matter_halo
So it's more weakly bound than most of the stars. Technically, it's outside the tidal radius:
https://academic.oup.com/mnras/article/366/2/429/1213793
That's literally what dark matter is. It's something else that bends space. It's called "dark" because no one knows what it is.
It's called "dark" because we can't see it, except for the gravitational effects it has on visible matter.
Neutrinos hardly interact at all with normal matter, as such it is a form of dark matter called hot dark matter[1].
However based on measurements we've ruled out[2] neutrinos as the main source of dark matter, hence we're looking for something else.
Since the only clue we have so far is the gravitational effect, it is possible that the solution is to modify the theory of gravity instead of finding new particles. People are looking into this as well. And heck, maybe it's both. Time will tell!
[1]: https://en.wikipedia.org/wiki/Hot_dark_matter
[2]: http://w.astro.berkeley.edu/~mwhite/darkmatter/hdm.html
It is rarely mentioned amongst all the Higgs back-slapping, that the Standard Model does not yet have a complete and verified theory of neutrino physics: masses? Majorana/Dirac? self-anti-particle? chiralities? ...
There may be right-handed neutrinos that do not interact via the weak force (which is maximally parity-violating). They would only interact gravitationally and play a role dark matter:
https://en.wikipedia.org/wiki/Sterile_neutrino