ISRO Missions and Discoveries

What are Globular Clusters?


From UPSC perspective, the following things are important :

Prelims level: Globular Cluster, Omega Centurari

Mains level: Not Much


Astronomers and scientists at the Indian Institute of Astrophysics (IIA) while studying the Omega Centauri have found that hot stars and white dwarfs emitted less ultraviolet radiation than expected.

Omega Centauri

  • It is the most massive globular cluster system in our galaxy.
  • It was first identified as a non-stellar object by Edmond Halley in 1677 and as globular star cluster orbiting Milky Way galaxy by John Herschel in 1830s.
  • It contains approximately 10 million stars and is about 16,000 light-years away.
  • It also includes stars of a variety of ages, whereas other globular clusters contain stars from only one generation.
  • It is the largest and brightest globular cluster in the Milky Way.

 What is a globular cluster?

  • A globular cluster is a spheroidal conglomeration of stars.
  • Globular clusters are bound together by gravity, with a higher concentration of stars towards their centres.
  • They can contain anywhere from tens of thousands to many millions of member stars.
  • They orbit mostly in the extended stellar halos surrounding most spiral galaxies.

How are they formed?

  • No one knows precisely how globular clusters formed. Or what role, if any, they played in the development of galaxies.
  • We know globular clusters are the oldest, largest and most massive type of star cluster. And globular clusters contain the oldest stars.
  • Their age is determined by their almost complete lack of what astronomers call metals, the heavier elements forged in star interiors.

Our Milky Way has over 150 globular clusters

  • Our own Milky Way has over 150 globular clusters, with perhaps more, hidden by galactic dust.
  • The Andromeda galaxy (M31), our neighboring spiral galaxy, appears to have around 300 globular clusters.

Difference between a globular cluster and an open cluster

  • Globular clusters are big, symmetric and old. They can reach 300 light-years in diameter and contain 10 million stars.  On the other hand, open star clusters, contains sibling stars, scattered through the disk of our galaxy and presumably other galaxies.
  • Globular star cluster are very symmetrical in shape, and are densest toward their centers. Open star clusters are irregular in shape and loosely grouped together.
  • Globular clusters orbit in the halo of our galaxy. Plus, center around the galaxy’s core and expanding above and below the galactic disk. Open star clusters tend to orbit within the disk.
  • Globular star clusters contain million of stars. Yet some globular clusters, like Omega Centauri, contain millions of stars. Open star clusters contain only hundreds of stars.


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