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Thread: Dwarf galaxy Dark Matter content is most revealing

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    Default Dwarf galaxy Dark Matter content is most revealing



    pikaia, helicon64, Solrian and 6 others like this.
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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    Very cool. It will be interesting to see how it pans out.
    Jim

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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    Quote Originally Posted by Solrian View Post
    Very cool. It will be interesting to see how it pans out.
    The fact that some dwarfs are chock full of dark matter (Dragonfly 44 for example) and others are relatively free from it is providing sleepless nights for MONDomaniacs.

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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    Here's another take that has a different interesting formation scenario than I imagined

    https://www.quantamagazine.org/a-vic...-any-20180328/
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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    Reading these articles has me repeatedly thinking that dark matter distribution must be at least as uneven as normal matter, and in areas with extremely sparse dark matter yet sufficient quantities of normal matter different mechanisms of galaxy formation dominate. These perhaps less complex interactionally if only due to a reduction in the quantity of influences in their formation. As regards whether structures low in DM would be more or less stable in regards to influences of other nearby objects I'm a bit uncertain making guesses.

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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    The difference in distribution of dark and normal matter is complicated because it is history dependent. DM is essential for making clusters of galaxies. You can't build the Virgo cluster without it. Normal matter by itself can only make globular cluster size objects at the Big Bang.

    Alternative gravity theories have trouble with making a universe with galaxies and clusters of galaxies.

    So for the most part the formation of cluster of galaxies and galaxies is a matter of DM clumping first then attracting normal matter to the clump. But this is "on average". Exceptions might occur as with the all DM and no DM cases.

    In an alternative gravity scenario exceptions are not allowed and their existence is falsifying.
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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    This statement from the phys.org article confuses me:

    "Star clusters are gravitationally bound collections of stars that orbit inside galaxies. Unlike galaxies, star clusters are so dense that their stars gravitationally scatter from one another causing them to slowly expand."

    If gravity is an attractive force, how does it cause stars in a star cluster to "gravitationally scatter"?
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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    Quote Originally Posted by RobinBaker View Post
    This statement from the phys.org article confuses me:

    "Star clusters are gravitationally bound collections of stars that orbit inside galaxies. Unlike galaxies, star clusters are so dense that their stars gravitationally scatter from one another causing them to slowly expand."

    If gravity is an attractive force, how does it cause stars in a star cluster to "gravitationally scatter"?
    The statement is slightly imprecise. Internally encounters among the cluster members are pretty neutral as far as expansion of the cluster is concerned. It can be pointed out that a close encounter between two cluster members can lead to the ejection of one of them. This actually causes the remainder of the cluster to contract a bit.

    However when the cluster stars are encountering field stars that are not cluster members that can cause the cluster to be less bound as a whole and to expand slightly. The theory of this effect was laid out by Chandrasekhar in 1943 so it's old news and well established. In general clusters dissipate over time. Even globulars lose members especially when passing through the disk of the galaxy.

    https://en.wikipedia.org/wiki/Dynamical_friction
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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    Dr H, who has disappointed by going over into MONDophilia, disagrees that the observations refute MOND.

    https://backreaction.blogspot.com/20...atter-has.html

    She's wrong and not in a way that is interesting.
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    Default Re: Dwarf galaxy Dark Matter content is most revealing

    I've long babbled about how the coincidence of the mass of globular clusters with the normal matter Jeans mass for collapse (without DM) is an indicator that globs may form differently from galaxies and clusters of galaxies. This take from AAS is therefore most welcome

    Globular Clusters Shine in a Galaxy Lacking Dark Matter

    Despite Dr H's defense of MONDomanian ideas the additional links at the bottom of the article spell additional sorrows for MONDophiles.
    Last edited by not_Fritz_Argelander; 04-11-2018 at 11:14 PM.
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