
The work of Vera Rubin - sohkamyung
https://astrobites.org/2016/12/27/how-one-person-discovered-the-majority-of-the-universe-the-work-of-vera-rubin/
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beters
The article was informative, but I generally dislike the "one person"
rhetoric. Barely one mention of Ford Jr., the other author on both papers.
Overstating Rubin's contribution seems unfair to those who have made dark
matter their life's work alongside her.

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jbmorgado
It's like if Watson just died and suddenly everyone just totally ignored Crick
was there with him discovering the DNA structure.

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trhway
>For a single star orbiting around an entire galaxy the only mass that matters
is the mass contained within the star’s orbit (the pull from mass outside of
this radius cancels out rather beautifully)

and the link on the "rather beautifully" points to spherical shell
calculations which disk galaxies are clearly not. Reminds that joke about
spherical cow in vacuum.

The mass outside of the star's orbit does matter. That outer ring mass'
gravity doesn't cancel itself out. The outer ring's segment closest to the
star pulls stronger than the total of the segments across the galaxy and that
itself provides for stars' velocities not being distributed according to the
naive spherical shell calculations. And the farther you're from the massive
galaxy center the less that naive spherical calculation reflects your
situation, and the more the disk based gravity calculation matters.

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antognini
You are correct that a spherical approximation is not correct, and indeed
generally won't be very good, especially in the disk of the Galaxy. In a
rigorous calculation of the Galaxy's potential, astronomers usually use five
components:

1\. The bulge, which is represented by a spheroidal potential

2\. The stellar disk, which is represented by two exponential potentials (one
radial, the other vertical)

3\. The interstellar medium, represented by a single exponential potential

4\. A bar, which generally doesn't have a simple analytic representation, but
can be represented by a series of ellipsoidal potentials

5\. A dark matter halo, represented by a two-component power law. The orbits
of stars require the existence of this component of the potential.

Interestingly, the dark matter halo is quite spherically symmetric and
comprises nearly all of the Galaxy's mass, so a spherical potential is _more_
correct the further away you get from the center!

