Tuesday, 7 April 2015
Hubble Space Telescope Views Globular Cluster Messier 22
This newly released Hubble image shows Messier 22, the brightest globular cluster visible from the northern hemisphere.
A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite. Globular clusters are very tightly bound by gravity, which gives them their spherical shapes and relatively high stellar densities toward their centers.
Messier 22 is located in the constellation Sagittarius, approximately 10,400 light-years away.
It was the first globular cluster to be discovered. German astronomer Johann Abraham Ihle found it on August 26, 1665, while observing Saturn.
The cluster, also known as M22 or NGC 6656, has a diameter of about 70 light-years and half a million solar masses.
According to astronomers, Messier 22 orbits the galactic center once every 200 million years.
The cluster is an easy object for the naked eye to see. Despite its relative proximity to us, the light from the cluster’s stars is not as bright as it should be as it is dimmed by dust and gas located between us and Messier 22.
As they are leftovers from the early Universe, globular clusters are popular study objects for astronomers.
Messier 22 has fascinating additional features: six planet-sized objects that are not orbiting a star have been detected in the cluster; it seems to host two black holes.
The cluster is one of only three ever found to host a planetary nebula – a short-lived gaseous shells ejected by massive stars at the ends of their lives.
Source : Sci-news