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Wednesday, May 9, 2012

VISTA image of Globular Cluster M55

VISTA image of Globular Cluster M55
Click on the image for full resolution (6.0 MB)

This striking view of the globular star cluster M55 (Messier 55) in the constellation of Sagittarius was obtained in infrared light with the VISTA survey telescope at ESO's Paranal Observatory in Chile. This vast ball of ancient stars is located at a distance of about 17 000 light-years from Earth. Globular clusters are held together in a tight spherical shape by gravity. In Messier 55, the stars certainly do keep close company: approximately one hundred thousand stars are packed within a sphere with a diameter of only about 25 times the distance between the Sun and the nearest star system, Alpha Centauri. About 160 globular clusters have been spotted encircling our galaxy, the Milky Way, mostly toward its bulging center. The two latest discoveries, made using VISTA, were recently announced. The largest galaxies can have thousands of these rich collections of stars in orbit around them. Observations of globular clusters' stars reveal that they originated around the same time - more than 10 billion years ago - and from the same cloud of gas. As this formative period was just a few billion years after the Big Bang, nearly all of the gas on hand was the simplest, lightest and most common in the cosmos: hydrogen, along with some helium and much smaller amounts of heavier chemical elements such as oxygen and nitrogen. Being made mostly from hydrogen distinguishes globular cluster residents from stars born in later eras, like our Sun, that are infused with heavier elements created in earlier generations of stars. The Sun lit up some 4.6 billion years ago, making it only about half as old as the elderly stars in most globular clusters. The chemical makeup of the cloud from which the Sun formed is reflected in the abundances of elements found throughout the Solar System - in asteroids, in the planets and in our own bodies.
The full resolution image weighs 6.0 MB, so please be patient when downloading!
Credit: ESO/J. Emerson/VISTA
Acknowledgment: Cambridge Astronomical Survey Unit
Image enhancement: Jean-Baptiste Faure

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