‘Ram-Pressure Stripping’ Shuts Off Star Formation in Galaxies, Astronomers Say
The study of 10,567 galaxies shows that their gas — the lifeblood for star formation — is being violently stripped away on a widespread scale throughout the local Universe.
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Tau.Neutrino said:
‘Ram-Pressure Stripping’ Shuts Off Star Formation in Galaxies, Astronomers SayThe study of 10,567 galaxies shows that their gas — the lifeblood for star formation — is being violently stripped away on a widespread scale throughout the local Universe.
More…
Do all galaxies have dark matter halos?
Tau.Neutrino said:
Tau.Neutrino said:
‘Ram-Pressure Stripping’ Shuts Off Star Formation in Galaxies, Astronomers SayThe study of 10,567 galaxies shows that their gas — the lifeblood for star formation — is being violently stripped away on a widespread scale throughout the local Universe.
More…
Do all galaxies have dark matter halos?
Yes, ram pressure strips gas out of galaxies.
Good question about dark matter halos. I strongly suspect that the answer is “no”. Spiral galaxies do. Drawf irregulars do. Globular clusters, I need to check but I think not. So those galaxies that most closely resemble the globular clusters – the dwarf ellipticals – may not.
I’d count this as a possible rather than certain galaxy without a dark matter halo.
https://www.newscientist.com/article/dn13280-galaxy-without-dark-matter-puzzles-astronomers/
In the spiral galaxy NGC 4736, however, the rotation slows down as you move farther out from the crowded inner reaches of the galaxy. At first glance, that declining rotation curve is just what you would expect if there is no extended halo of dark matter, and no modification to gravity. As you move far away from the swarming stars of the inner galaxy, gravity becomes weaker, and so motions become more sedate.
The rotation measurements only stretch 35,000 light years out from the galactic centre, which is not far enough to confirm that first impression. So a team of astronomers in Poland developed a more sophisticated analysis.
Joanna Jalocha, Lukasz Bratek and Marek Kutschera of the Polish Academy of Science in Krakow have found a way to splice the rotation curve together with another measurement: the density of hydrogen gas far from the galactic centre.
According to their combined mathematical model, ordinary luminous stars and gas can indeed account for all the mass in NGC 4736.
“If this paper is correct, then this galaxy contains very little or no dark matter,”
Checking up dark matter in globular clusters.
Globular clusters do have dark matter, up to a maximum of 1.5 times the visible matter. But some have less dark matter. 47 Tuc has dark matter that is at most one third of the visible matter.
I was wrong about dwarf ellipticals, they have much more dark matter than the visually similar globular clusters.
mollwollfumble said:
I was wrong about dwarf ellipticals, they have much more dark matter than the visually similar globular clusters.
On the other hand, one article hypothesis that there may be two different types of dwarf ellipticals. One is primordial and contains heaps of dark matter. The other is called “tidal” and is formed by a galaxy collision. Tidal dwarf galaxies contain much less dark matter. This is still just a hypothesis.
so its reasonable to say then that most galaxies have dark matter halos?
Tau.Neutrino said:
so its reasonable to say then that most galaxies have dark matter halos?
Absolutely.