Milky Way’s Formation Process Had an 11 Billion Years Old Witness

The Milky Way galaxy has gotten its impressive size by consuming smaller galaxies, but until now, experts weren’t able to document this process. However, now, a team of astronomers has found a star that can offer some pieces of information on the exact moment one of the collisions took place.

Nu Indi, or HD 211998, is a star located about 94 light-years from Earth and is visible in the night sky. Experts had now discovered that this object is from the early leftovers of the Milky Way, back when the galaxy was absorbing everything as it took the shape it has today.  

Nu Indi’s Movement Across the Milky Way  

According to data collected in the last decades, approximately 11 billion years ago, the Milky Way crashed with a satellite galaxy known as Gaia-Enceladus, or Gaia Sausage. This satellite galaxy was the most massive satellite galaxy ever consumed by the Milky Way, and when the event took place, it pushed Nu Indi, which has always been a part of our galactic zone, out of its place.  

Back then, the star had only taken form and was included in the Milky Way’s early record. Data gathered on stars also detail what chemical materials they are made of, which would indicate the places they definitely have formed in. For instance, a star filled with hydrogen would have taken shape in an area rich in hydrogen, which is in the southern constellation of Indus.

Nu Indi in the night sky. [Image: ESA]
Using the European Space Agency’s or ESA’s Gaia satellite, which is currently analyzing the Milky Way, astronomers have been able to recreate Nu Indi’s movement across the galaxy. Merging the mapping data, as well as 3D information gathered from NASA’s Transiting Exoplanet Survey Satellite (TESS), researchers were able to design a clear picture of Nu Indi, which is approximately three times the size of the Sun, but with only about 85 percent of the star’s mass.  

Cutting-Edge Data  

Bill Chaplin, Professor of Astrophysics at the University of Birmingham and lead author of the study, said: “Since the motion of Nu Indi was affected by the Gaia-Enceladus collision, the collision must have happened once the star had formed. That is how we have been able to use the asteroseismically-determined age to place new limits on when the Gaia-Enceladus event occurred.”  

Co-author Dr. Ted Mackereth, also from Birmingham, further explained: “Because we see so many stars from Gaia-Enceladus, we think it must have had a large impact on the evolution of our galaxy. Understanding that is now a very hot topic in astronomy and this study is an important step in understanding when this collision occurred.”  

Moreover, according to Dr. Saskia Hekker, head of the research team, the chronological classification not only helps experts better understand the way the crash changed our galaxy, but it also provides a bit of information on how collisions and mergers affected other galaxies and impacted their evolution.  

This research proves the potential of asteroseismology with NASA’s TESS instrument, and what is possible when there is a lot of available groundbreaking data on a single, bright star, Chaplin said. 

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