Astronomers believe that our Milky Way galaxy, approximately 13.6 billion years old, has ingested many smaller galaxies over its lifetime, however, it has previously proved hard to determine the precise time at which these mergers occurred.
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. In July of last year, The scientists dated one of those periods of galactic cannibalism that occurred about 10 billion years ago., when the Milky Way ate the dwarf galaxy known as Gaia-Enceladus.
The Milky Way, our stunning home galaxy, is like a cosmic Hannibal Lecter, having gobbled up smaller galaxies as it evolved. As the merger progressed, it altered nu Indi's orbit around the center of the Milky Way, providing a marker for when the merger happened.
In order to know exactly how it may have affected our galaxy, they needed an exact date. One of them is the dwarf galaxy Gaia-Enceladus. To this end, the researchers led by Prof.
The star that became the focus of a new study by astronomers has been identified as Nu Indi. The worldwide collaboration of over 80 scientists studied a single, very bright star approximately 95 light-years from Earth known as "ν Indi", which can be seen with the naked eye. Launched in 2018, TESS is surveying stars across numerous sky to stare planets orbiting the celebrities and to behold the celebrities themselves. Through the star, the astronomers learned that the Milky Way devoured its neighbor billions of years ago.
In addition, the Transiting Exoplanet Survey Satellite (TESS) indicated that v Indi is located in the region of space where the Milky Way ate up Gaia-Enceladus. Through a combination of accurate galactic mapping data, spectroscopy, stellar kinematics and asteroseismology, observations of this singular star have now revealed our galaxy's violent past.
"Since the motion of v Indi was affected by the Gaia-Enceladus collision, the collision must have happened once the star had formed", lead author of the study Bill Chaplin, professor of astrophysics at the University of Birmingham is quoted by ScienceDaily as saying. So, if you can place the age of the star, you can place constraints on when the collision occurred.
To determine the age of a star, researchers use its natural oscillations, which can be observed as brightness fluctuations. The scientists said this star, nu Indi, was already orbiting inside the smaller Milky Way prior to the Gaia-Enceladus collision, which unfolded over millions of years. Further analysis suggested the collision took place between 8 and 11 billion years ago (the Universe is around 13.8 billion years old).
"Similar to the way seismic waves on Earth allow conclusions about the interior of our planet, stellar oscillations help us to reveal the internal structure and composition of the star and thus its age", explains Nathalie Themessl, co-author of the study. "This chronological classification not only helps us to understand how the collision changed our galaxy", says Hekker. "It also gives us a sense, of how collisions and mergers impacted other galaxies and influenced their evolution".