Cosmic lens reveals faint radio galaxy
phys.org
phys.org
If DM is still needed to account for galaxy-cluster lensing, would that suggest DM is much more diffuse than hadronic matter? Would that imply low-mass DM particles, or much more slowly-cooling DM, something else, or indeterminate?
Am I misremembering, or had normal low-mass DM particles already been ruled out? How is DM supposed to cool, anyway?
TIA
I don't see that in the article? They centered on galaxy clusters which contain huge amounts of dark matter. DM is needed to account for lensing. There isn't enough mass in the stuff we can see to account for the lensing signal.
> How is DM supposed to cool, anyway
It can't! The way that normal matter cools is by radiating (giving off light). Dark matter doesn't radiate (if it did, we would be able to see it). So, while normal matter cools and settles to the center of the gravity well, dark matter doesn't and (as you say) forms physically larger structures.
Usually we hear about lensing by galaxy clusters, not individual galaxies. If galaxies are short on DM, but clusters aren't, that seems to say something about how DM is distributed.
[0] <https://www.sciencedaily.com/releases/2021/03/210304145458.h...>
[1] <https://phys.org/news/2014-06-herschel-key-discovery-spectac...>
VHS? Betamax