Some of the oldest stars in the Universe have just been discovered. Not at the far reaches of our Universe by an experienced team using the powerful James-Webb space telescope. Rather, by undergraduate students in decade-old data and within our very own Milky Way.
Shortly after the Big Bang around 13.8 billion years ago, the Universe was primarily composed of hydrogen and helium with trace amounts of other chemical elements. This is one method astronomers can use to search for the first stars in our Universe by looking for traces of strontium, barium, or iron in the spectra of stars collected by telescopes.
A group of undergraduate students from MIT (Massachusetts Institute of Technology) has discovered three stars that formed 12 to 13 billion years ago. These stars had been observed by the Magellan telescope about a decade ago, but their spectra had not been studied in this way. They are located in the halo of our own Milky Way, just 30,000 light-years away from Earth.
In the Monthly Notices of the Royal Astronomical Society, researchers describe how, after analyzing data from the Gaia mission, they realized that these stars exhibit retrograde motion, meaning they rotate in the opposite direction compared to the rest of the galactic disk and even the halo. According to astronomers, this indicates that these stars, among the oldest in our Universe, belonged to ancient dwarf galaxies.
Small Accreted Stellar Systems: Ancient Stars in the Milky Way
Researchers have identified a group of small galaxies that fell into our Milky Way and continued on their trajectory even after being integrated into our Galaxy. These galaxies are now referred to as “Small Accreted Stellar Systems” (SASS).
Ancient Stars to Look for in the Milky Way
In scientific literature, the team has identified 65 other stars with low abundance of strontium and barium that also appeared to be moving in a retrograde manner at hundreds of kilometers per second. Anna Frebel, a professor of physics, commented, “It’s as if they are fleeing! We don’t know why.” Further exploration of ancient stars in the Milky Way using this method may provide insights into this intriguing phenomenon.