Collision helped make the Milky Way - and now we know when

James Marshall
January 14, 2020

"That is how we have been able to use the asteroseismically-determined age to place new limits on when the Gaia-Enceladus event occurred". The merger - a collision, actually - reports astronomers at Yale University, happened 11.5 billion years ago when a small galaxy called Gaia-Enceladus slammed into what then existed of the Milky Way, Earth's home galaxy, which is about 13.5 billion years old.

A team of researchers including scientists from the Max Planck Institute for Solar System Research (MPS) in Germany for the first time used a single star affected by the collision as a clue for dating.

Just like Hungry Hungry Hippos gobbles up anything that gets in its way, the Milky Way gobbled up another galaxy in its early days - Gaia Enceladus. For example, the smaller galaxy introduces stars with a different chemical composition, the motion of many stars is altered, and myriads of new stars are formed. "Understanding that is now a very hot topic in astronomy, and this study is an important step in understanding when this collision occurred", concluded the study's co-author, Dr. Ted Mackereth, a galactic archaeology research fellow at the University. To this end, the researchers led by Prof.

The star - v Indi, in the constellation Indus - is about 95 light-years away and can be seen with the naked eye. Launched in 2018, TESS is surveying stars across most of the sky to search for planets orbiting those stars and to study the stars themselves.

The star that became the focus of a new study by astronomers has been identified as Nu Indi. He and a list of co-authors, affiliated with the Stellar Astrophysics Centre (SAC) at Aarhus University, Resorted to a novel approach by applying the forensic characterisation of a single ancient, bright star called ν Indi to probe the history of the Milky Way.

Using the European Space Agency's (ESA's) Gaia satellite, which is mapping the Milky Way, experts have been able to reconstruct Nu Indi's movement across the galaxy.

"Since the motion of Nu Indi was affected by the Gaia-Enceladus collision, the collision must have happened once the star had formed", astrophysicist William Chaplin, one of the authors of the study, said in a statement. So, if you can place the age of the star, you can place constraints on when the collision occurred.

Scientists were able to observe the star for its oscillation frequency, directly linked to its mass and age and clubbed it with other awesome techniques to gauge its light spectrum, its relative position and orbit and its motion through space to determine its profile. When this discovery was made last year, the scientists only knew that whatever had happened, happened over 10 billion years ago. Researchers confirm in the study that the collision had to have started between 11.6 and 13.2 billion years ago, if the merger is allowed time to propagate through the galaxy.

Dr Saskia Hekker, head of the research group, said: "This chronological classification not only helps us to understand how the collision changed our galaxy". "It also gives us a sense, of how collisions and mergers impacted other galaxies and influenced their evolution".

Other reports by Click Lancashire

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