The decay of radioactive isotope potassium 40 to argon 40 is one of the main ways of finding the age of rocks: see Potassium-argon dating at Wikipedia.
But on the moon, the Apollo missions found much more argon 40 than could be explained by potassium decay. Other explanations don't look so great either, see: On the question of the 40Ar excess in lunar soils.
Friday, March 04, 2011
Globular clusters have little dark matter
Apparently globular clusters have little or no dark matter:
Evidence Against Dark Matter Halos Surrounding the Globular Clusters MGC1 and NGC 2419. This preprint also finds the motion of stars in these globular clusters is consistent with Newtonian gravity and not MOND, even though the clusters are in the low acceleration range in which MOND is supposed to make a difference. However previous see the blog post Velocities in Globular Clusters for a report that MOND does work in GCs!
Maybe globular clusters originated as the nuclear cluster of a galaxy: the preprint Nuclear Star Clusters mentions this as a possibility while discussing the star clusters at the center of galaxies.
In contrast Dwarf spheroidal galaxies are dark matter dominated.
Evidence Against Dark Matter Halos Surrounding the Globular Clusters MGC1 and NGC 2419. This preprint also finds the motion of stars in these globular clusters is consistent with Newtonian gravity and not MOND, even though the clusters are in the low acceleration range in which MOND is supposed to make a difference. However previous see the blog post Velocities in Globular Clusters for a report that MOND does work in GCs!
Maybe globular clusters originated as the nuclear cluster of a galaxy: the preprint Nuclear Star Clusters mentions this as a possibility while discussing the star clusters at the center of galaxies.
In contrast Dwarf spheroidal galaxies are dark matter dominated.
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