GCl 38
GCl 38 is a globular cluster located in the
constellation Hercules.
It was discovered in 1958 by Sidney van den Bergh and Halton Arp during inspection of the photographic plates from the Palomar Sky Survey.
This is a round, diffuse cluster located in the outer
halo of the Milky Way galaxy. It is about 3-4 billion years younger than a typical galactic cluster.
The metallicity of the cluster is = −1.50, indicating a lower abundance of elements with mass greater that helium compared to the Sun. The combined mass of the main sequence stars in the cluster is, and the combined mass of observed stars within the half-light radius is . These mass estimates provide lower bounds for determining the total mass of the cluster. The median radial velocity of stars within the cluster is.
Because of the cluster's location on the outer fringes of the Milky Way, it was used as a test case for modified newtonian dynamics. This is an alternative hypothesis to explain the galactic rotation problem.
