Observations by European Gaia instrument rewrites dramatic history of Milky WayThe European Gaia instrument is on a mission to precisely map the positions of a billion nearby stars and track their motions.
Research based on the observations by the instrument has upended the conventional theory of the formation of the Milky Way.
The halo of stars around the Milky Way has wrinkles in it, suggesting a recent merger event.
New Delhi: Large spiral galaxies such as our Milky Way are formed from a series of collisions and mergers.
One of the study authors, Robyn Sanderson says, “The controversy is about when the Milky Way took in these stars.
Observations by European Gaia instrument rewrites dramatic history of Milky Way
The European Gaia instrument is on a mission to precisely map the positions of a billion nearby stars and track their motions. Research based on the observations by the instrument has upended the conventional theory of the formation of the Milky Way.
The halo of stars around the Milky Way has wrinkles in it, suggesting a recent merger event. (Image Credit: Halo stars: ESA/Gaia/DPAC, T Donlon et al. 2024; Background Milky Way and Magellanic Clouds: Stefan Payne-Wardenaar).
New Delhi: Large spiral galaxies such as our Milky Way are formed from a series of collisions and mergers. The Milky Way began forming about 13.6 billion years ago, from a proto-galactic cloud shortly after the Big Bang. According to the conventional theory on the formation of the Milky Way, there were a series of merger events that eventually led to the formation of the large, spiral galaxy that we live in.
The series of mergers leading to the Milky Way
A merger with a dwarf galaxy called Gaia-Enceladus-Sausage between 10 and 11 billion years ago contributed significantly to the halo and the dark disc of the galaxy. Then there were merger events with a fragment of a dwarf galaxy, the Helmi stream, between 8 and 11 billion years ago, a merger with the Sequoia dwarf galaxy around 9 billion years ago, and a merger with the Kraken dwarf galaxy between 6 and 9 billion years ago.
There was also a merger with dwarf galaxy in a nearly radial orbit around three billion years ago, known as the Virgo radial merger. The other merger events are so recent that they are ongoing, such as the merger with the Sagittarius Dwarf Galaxy, and the ongoing mergers with the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC).
New research challenges theory
Now, data from the Gaia instrument indicates that the last significant merger event, that of the Gaia-Sausage-Enceladus galaxy did not occur between 8 and 11 billion years ago, as previously believed. The research indicates that the stars in the halo of the Milky Way, which is a diffuse clouds that extends in all directions around the central disc, has too many wrinkles in it, and does not have a uniform distribution. These wrinkles indicate that the merger event was more recent.
A paper describing the findings has been published in the Monthly Notices of the Royal Astronomical Society. One of the study authors, Robyn Sanderson says, “The controversy is about when the Milky Way took in these stars. Our study shows some stars, thought to be from an old merger, couldn’t be. The pattern that we see them forming would have changed or faded away by now.”
