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STELLAR HALO
Why in news?
Recently, Astronomers have detected in the stellar halo that represents the Milky Way's outer limits a group of stars more distant from Earth than any known within our own galaxy - almost halfway to a neighbouring galaxy.
About Stellar Halo:
- A stellar halo is an essentially spherical population of stars and globular clusters thought to surround most disk galaxies and the cD class of elliptical galaxies.
- Only about 1% of a galaxy’s stellar mass resides in its halo, and due to this low luminosity, the observation of halos in other galaxies is extremely difficult.
- In contrast to the thin and thick disk of disk galaxies, the halo generally has no net rotation and is supported almost entirely by velocity dispersion.
- The halo stars in the Milky Way are generally old, with most having ages greater than 12 billion years.
- These ages are similar to those of bulge and globular cluster stars, meaning that stars in the halo were probably among the first Galactic objects to form.
- Due to its old age, understanding the processes which led to the formation of the stellar halo is key in unravelling the evolutionary history of the Milky Way.
- The halo stars of the Milky Way are generally metal-poor, with a metallicity distribution that peaks at around 1/30 of the solar value.
- The lowest metallicity star found in the Milky Way to date, is a halo star with a metallicity of approximately 1/200,000 of the solar value.