Astronomers using the NASA/ESA Hubble Space Telescope have captured the brilliance of a globular cluster called NGC 6558.
This Hubble image shows NGC 6558, a globular cluster located 23,000 light-years away in the constellation of Sagittarius. The color image was made from separate exposures taken in the visible and near-infrared regions of the spectrum with Hubble’s Advanced Camera for Surveys (ACS) instrument. It is based on data obtained through two filters. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / R. Cohen.
Globular clusters are dense systems of very ancient stars, gravitationally bound into a single structure about 100-200 light-years across.
The word globulus, from which these clusters take their name, is Latin for small sphere.
Globular clusters are among the oldest known objects in the Universe and are relics of the first epochs of galaxy formation.
They contain hundreds of thousands or perhaps a million stars. The large mass in the rich stellar center of a cluster pulls the stars inward to form a ball of stars.
It is thought that every galaxy has a population of globular clusters. Some, like our Milky Way Galaxy, have a few hundred, while elliptical galaxies can have several thousand.
“Globular clusters equip us with interesting natural laboratories in which to test our theories, as all the stars in a globular cluster formed at approximately the same time with similar initial composition,” Hubble astronomers said.
“These stellar clusters therefore provide unique insights into how different stars evolve under similar conditions.”
NGC 6558 lies approximately 23,000 light-years away in the constellation of Sagittarius and is closer to the center of the Milky Way than Earth is.
Otherwise known as ESO 456-62 and GCl 89, this cluster was discovered in 1784 by the German-born British astronomer William Herschel.
The new image of NGC 6558 comes from a set of observations investigating globular clusters in the inner Milky Way.
The astronomers were interested in studying these globular clusters to gain greater insight into how globular clusters in the inner Milky Way form and evolve.
“As this Hubble observation shows, the stars in globular clusters can be densely packed,” they said.
“This image of NGC 6558 is thronged with stars in a rich variety of hues.”
“Some of the brightest inhabitants of this globular cluster are surrounded by prominent diffraction spikes, which are imaging artifacts caused by starlight interacting with the inner workings of Hubble,” they added.
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