STELLAR HALO | UPSC Current Affairs

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Context

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

The stellar haloof a galaxy refers to the component of its galactic halo containing stars. The halo extends far outside a galaxy's brightest regions and typically contains its oldest and most metal poor stars.

Structure and Properties

In the Lambda-CDM modelof the universe, galaxies grow by mergers. Such mergers are the cause of substructure observed in the stellar halo of galaxies; streams of stars from disrupted satellite galaxies are detectable through their coherence in space or velocity; a number of these streams are observable around the Milky Way.
As a result of the buildup from an assortment of satellite galaxies, variations in properties such as metallicityare present across stellar populations in halos.
Astrophysical simulationsof galaxies have predicted that stellar halos should have two components; one inner region dominated by stars which formed within the galaxy, and an outer region primarily composed of stars accreted through merger events. Predictions for these components include different structure and rotation directions.^[11] Observational evidence for this dual halo in the Milky Way has been claimed but contested.