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Thread: The speed of dark matter

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    Default The speed of dark matter



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    Default Re: The speed of dark matter

    Isn't this paper more about the association of dark matter with stars rather than the actual speed of DM? Considering that we don't know what (or if) the DM particle is, how do we measure its speed? Do we expect the speed of a DM particle to be constant, like the speed of light, or to vary based on gravitational and weak force effects?
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    Default Re: The speed of dark matter

    Quote Originally Posted by stargazer55 View Post
    Isn't this paper more about the association of dark matter with stars rather than the actual speed of DM? Considering that we don't know what (or if) the DM particle is, how do we measure its speed? Do we expect the speed of a DM particle to be constant, like the speed of light, or to vary based on gravitational and weak force effects?
    Not at all. If a large galaxy eats a smaller one the speed of the stream of low metallicity stars and DM from that smaller galaxy should be the same. Thus the low metal stars velocity should be a decent measure of the DM velocity. The velocities of the DM and stellar streams are well correlated.

    There is no reason for DM to have a constant speed. It's speed(s) should reflect the conditions of its capture. In turn those speeds determine its distribution in the galaxy halo.
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    Default Re: The speed of dark matter

    Quote Originally Posted by nFA View Post
    Not at all. If a large galaxy eats a smaller one the speed of the stream of low metallicity stars and DM from that smaller galaxy should be the same. Thus the low metal stars velocity should be a decent measure of the DM velocity. The velocities of the DM and stellar streams are well correlated.
    Is this because of the gravitational attraction between DM and the star?

    Quote Originally Posted by nFA View Post
    There is no reason for DM to have a constant speed. It's speed(s) should reflect the conditions of its capture. In turn those speeds determine its distribution in the galaxy halo.
    Do we know anything about the relative speed of DM traveling within our galaxy versus the DM in the halo? What happens to the speed of DM when it is no longer associated with normal matter compared to when it is?
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    Default Re: The speed of dark matter

    Quote Originally Posted by stargazer55 View Post
    Is this because of the gravitational attraction between DM and the star?
    It is because the DM and the stream of stars were initially gravitationally bound and comoving.

    Do we know anything about the relative speed of DM traveling within our galaxy versus the DM in the halo? What happens to the speed of DM when it is no longer associated with normal matter compared to when it is?
    All the DM is in the halo. Only the speeds associated with streams can be known so far. The speed of DM in the MW proper must be less than escape velocity.
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