The Milky Way Gobbled Up Another Galaxy, And This Star Saw It Happen

Astronomers recently discovered an extraordinary cosmic phenomenon that changed the way for the Milky Way. As per the ESA’s ongoing Gaia galactic survey, our home galaxy collided with another satellite galaxy called Gaia-Enceladus, and this collision gave it its puffy disk and a halo full of stars. Now, a single star has revealed our galaxy’s violent past and its observations have given us a more precise time frame for that event.

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It is called Nu Indi (HD 211998) and is located 94 light-years away in the southern constellation of Indus. As far as we can tell, Gaia-Enceladus was the largest galaxy ever devoured by the Milky Way. The current study is based on the three-dimensional map of the galaxy’s stars and it altered the Nu Indi’s movement through the galaxy. Scientists exploited its visible nature and combined it with accurate galactic mapping data, spectroscopy, stellar kinematics and asteroseismology to track its motion and concluded that the collision must have occurred once the star had formed.

Spectroscopic analysis of the chemical composition of Nu Indi indicated that it is born right here in the Milky Way. The metal-poor star is about three times the size of the Sun and about 85 per cent of its mass was previously believed to be over 9 billion years old. But, asteroseismological data from NASA’s Transiting Exoplanet Survey Satellite (TESS) indicates that Nu Indi is around 11 billion years old. 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.

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We know that metals didn’t exist till some stars had gone supernova, creating heavy elements that went on being incorporated into subsequent generations. The fact that Nu Indi only has about 3 per cent of the Sun’s iron abundance indicates it’s pretty old.

Scientists were able to observe the star for its oscillation frequency, directly linked to its mass and age and clubbed it with other amazing techniques to gauge its light spectrum, its relative position and orbit and its motion through space to determine its profile. Nu Indi can thus go a long way in helping us understand the evolution of the Milky Way.

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