Study puts dark matter back into elliptical galaxies

[ToSeek]

Study puts dark matter back into elliptical galaxies (http://www.spaceflightnow.com/news/n0509/28darkmatter/)

According to the prevailing "cold dark matter" theory of the evolution of the universe, every galaxy is surrounded by a halo of dark matter that can only be detected indirectly by observing its gravitational effects. This theory faced a challenge in 2003, when a team of astronomers reported a surprising absence of dark matter in elliptical galaxies. But a new analysis published in the September 29 issue of the journal Nature provides an explanation for the earlier observations that fits comfortably with the standard theory and puts the dark matter back into elliptical galaxies.

[dgruss23]

Interesting. So Primack's argument is that the velocity dispersion decreases at greater distance because of the shape of the orbits (highly elliptical) and the line of sight. Still, I'm curious what makes them think that the planetary nebula specifically should all have the highly elliptical orbits when they suggest other components of the system should have more circular orbits.

Of course the planetary nebula are not the only tracers of dark matter in elliptical galaxies. Some of the galaxies that indicated no dark matter - also indicated no dark matter by other means I believe. I have a file on that. I'll have to check it later.