Ancient collision of the Milky Way with another galaxy dated

Datada una antigua colision de la Via Lactea con otra galaxia

The merger of our galaxy with a smaller one called Gaia-Enceladus began between 11.6 and 13.2 billion years ago, as reflected by the oscillations of a bright star. This is indicated by an international study in which scientists from the CSIC have participated and data from the TESS missions of NASA and Gaia of the European Space Agency have been used.


<p>Recreation of the Milky Way merger and image provided by the TESS mission of the southern area of the sky showing the location of ν Indi (blue circle), the plane of the Milky Way (bottom) and the southern ecliptic pole (top) . / IAC - T. Mackereth</p>


Recreation of the Milky Way merger and image provided by the TESS mission of the southern area of the sky showing the location of ν Indi (blue circle), the plane of the Milky Way (bottom) and the southern ecliptic pole (top) . / IAC – T. Mackereth

A bright star called ν India, located in the Indus constellation and visible from the southern hemisphere, has revealed new details of an ancient collision that the Milky Way suffered with another smaller galaxy, Gaia-Enceladus.

An international team of researchers, with the participation of the Higher Council for Scientific Research (CSIC), has managed to date this collision, which occurred in the earliest history of our galaxy. The results are published this week in the journal Nature Astronomy.

The oscillations of the bright star ν Indi have allowed us to deduce its age and that our galaxy merged with another between 1,600 and 13,200 million years ago

Throughout its history the Milky Way has absorbed multiple smaller galaxies, although the stellar populations can be identified as 'kinematically differentiated structures (related to their movement)', it is generally difficult to date precisely when mergers occurred.

Now researchers have relied on natural oscillations detected in that star to determine that it was born a few years ago. 11.5 billion years. Subsequently, the collision with Gaia-Enceladus altered its movement through the Milky Way.

Knowing the age of this star and how it was kinematically heated by galactic fusion, the authors have been able to deduce that that collision between our galaxy and the other could have started between 11,600 and 13,200 million years, with a trusty 68% and 95% respectively.

To extract the information from ν Indi, the authors have combined data from the missions Transiting Exoplanet Survey Satellite (TESS) from NASA and Gaia from the European Space Agency (ESA), as well as information provided by ground-based observatories.

“Stars contain fossilized records of their histories and, therefore, the environment in which they were formed; and this work is based on the characterization of one of them to study the history of the Milky Way,” says the co-author. Aldo Serenelli, CSIC researcher in the Institute of Space Sciences.

The help of asteroseismology

“Using asteroseismology,” he adds, “a technique that studies the internal structure of pulsating stars, it has been possible to establish new limits to the time at which the Gaia-Enceladus event occurred.”

The existence in the Milky Way of many stars from Gaia-Enceladus indicates that the collision had a great impact on the evolution of our galaxy. “Understanding this is of great importance in astronomy today, and this study represents an important step in determining exactly when this collision took place,” highlights Serenelli.

According to the authors, the work also demonstrates the potential of asteroseismology based on data obtained by TESS and the possibilities that exist when observations on a single bright star can be combined with state-of-the-art instruments.

Bibliographic reference:

William J. Chaplin et Al. “Age dating of an early Milky Way merger via asteroseismology of the nakedeye star ν Indi.” Nature Astronomy. DOI: 10.1038/s41550-019-0975-9