Research Highlight

A merger with dwarf galaxies shaped the Milky Way

doi:10.1038/nindia.2020.10 Published online 21 January 2020

Since its birth, the Milky Way, home to our sun and billions of other stars, has merged with multiple smaller satellite galaxies. However, it is difficult to precisely date the age of such mergers.

By determining the age of a bright, metal-poor star, astrophysicists have now calculated when and how the Milky Way merged with Gaia-Enceladus, a dwarf galaxy1.

The bright star, visible to the naked eye, reveals that the merger, lasting for 2 billion years, shaped the Milky Way by accelerating star formation in it. This research, they say, will shed light on the evolution of the Milky Way.

Combining a host of techniques including observational studies, an international research team, including scientists from the Tata Institute of Fundamental Research in Mumbai, India, estimated that the star, named v Indi, has an abundance of iron, titanium and 20 different elements.

They found that the star churned out elements heavier than carbon through nuclear reactions involving helium. This analysis revealed that the star’s age exceeds 9.5 billion years.

The researchers report that the star was probably born more than 11 billion years ago. It bears hallmarks consistent with having been heated by the collision between the Milky Way and Gaia–Enceladus, they write.

Its age, they say, implies that the earliest the merger could have begun was between 11.6 and 13.2 billion years ago.


1. Chaplin, W. J. et al. Age dating of an early Milky Way merger via asteroseismology of the naked-eye star ν Indi. Nat. Astron. (2020) doi: 10.1038/s41550-019-0975-9