NGC 6355 is a globular cluster some 31,000 light-years away in the constellation of Ophiuchus.
This Hubble image shows the globular cluster NGC 6355; towards the center the stars become even more dense in a circular region, and also more blue; around the edges there are some redder foreground stars, and many small stars in the background. Image credit: NASA / ESA / Hubble / E. Noyola / R. Cohen.
Globular clusters are densely packed, spherical collections of hundreds of thousands or even millions of stars.
They are among the oldest known objects in the Universe and are preferentially associated with the oldest components of galaxies.
Our own Milky Way Galaxy hosts at least 150 such objects and a few more are likely to exist hidden behind the Galaxy’s thick disk.
“Globular clusters are stable, tightly bound clusters of tens of thousands to millions of stars, and can be found in all types of galaxy,” Hubble astronomers said.
“Their dense populations of stars and mutual gravitational attraction give these clusters a roughly spherical shape, with a bright concentration of stars surrounded by an increasingly sparse sprinkling of stars.”
NGC 6355 is located approximately 31,000 light-years away in the constellation of Ophiuchus.
Otherwise known as ESO 519-15 and GCl 63, it was discovered by the German-born British astronomer William Herschel on May 24, 1784.
“The dense, bright core of NGC 6355 was picked out in crystal-clear detail by Hubble in this image, and is the crowded area of stars towards the image’s center,” the astronomers said.
“With its vantage point above the distortions of the atmosphere, Hubble has revolutionized the study of globular clusters.”
“It is almost impossible to distinguish the stars in globular clusters from one another with ground-based telescopes, but astronomers have been able to use Hubble to study the constituent stars of globular clusters in detail.”
The color image of NGC 6355 was made from separate exposures taken in the visible and near-infrared regions of the spectrum with Hubble’s Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3).
It is based on data obtained through four filters. The color results from assigning different hues to each monochromatic image associated with an individual filter.
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