Omega Centauri — Discovered by Edmond Halley in 1677.
About 10 million stars orbit the center of this globular cluster – named Omega Centauri – as this giant globular cluster orbits our Galactic center.
Recent evidence indicates that Omega Centauri is by far the most massive of the about 150 known globular clusters in the Milky Way.
Omega Centauri, cataloged as NGC 5139, spans about 150 light years across, lies about 15,000 light years away, and can be seen without visual aid toward the constellation of Centaurus.
The stars in globular clusters are generally older, redder and less massive than our Sun. Studying globular clusters tells us not only about the history of our Galaxy but also limits the age of the universe.
In 1999, a team led by Young-Wook Lee of Yonsei University, South Korea, obtained a color-magnitude diagram (CMD) for 50,000 member stars of Omega Centauri with the 0.9-m telescope of CTIO in Chile.
Studies of this CMD indicate that the stars of this cluster did not all form at once but over a 2-billion-year period of time, with several starburst peaks. This was the first time that multiple populations were found in a globular cluster.
The team who carried out this work speculates that this result may indicate that Omega Centauri might be the remnant of a nucleus of a small galaxy which has merged with our Milky Way.
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Omega Centauri had been listed in Ptolemy’s catalog as a star. Halley was the first to document its nonstellar nature, and listed it as “luminous spot or patch in Centaurus” in his historical list of six such objects. Lacaille included it in his catalog as number I.5.