A team from the Massachusetts Institute of Technology (MIT) has discovered three of the oldest stars in the universe, and what’s surprising is that they’re not in a distant galaxy visible only to the super-powerful James Webb Space Telescope: They’re on our galactic fringe, in the “halo” of the Milky Way. The study was published in the journal Nature on May 14. Monthly Bulletin of the Royal Astronomical Society.
The Milky Way’s halo is a cloud of stars that envelops the entire galactic disk, the main disk of the Milky Way. The team believes that the three stars formed 12 to 13 billion years ago, when the universe was just starting to take shape. Stars in compact condensed star systems(or SASS), and each star likely belonged to its own small galaxy that was at one point absorbed into the larger, ever-growing Milky Way. Today, these three stars are all that’s left of their former galaxies.
They orbit the outer edges of the Milky Way galaxy, where older, more enduring stars may lurk, according to the team.
“Given what we know about galaxy formation, these oldest stars should definitely exist,” says MIT astronomer and astrophysicist Anna Frebel. He said in a statement via MIT News.“They’re part of our cosmic genealogy, and now we have a new way to find them.”
[Related: Youth-stealing stars could explain ‘missing giants’ at the Milky Way’s center.]
The study grew out of a classroom concept Frebel is launching for the fall 2022 semester. A course called Observational Stellar ArchaeologyIn this class, students learned the techniques needed to analyze ancient stars and then applied them to previously unstudied stars to understand their origins, including several undergraduate and graduate students who are co-authors on the new study.
“Most of our classes teach the fundamentals, but this class immediately brought us to the forefront of astrophysics research,” says Hilary Anderes, a co-author of the study and an MIT class of 2023 student. It said in a statement.
The class was looking for ancient stars that formed shortly after the Big Bang, about 13.8 billion years ago, when the universe was made up mostly of helium and hydrogen, with less of other chemical elements like barium and strontium. The class pored over data that Frebel had collected over the years. Magellan Clay Telescope at Las Campanas Observatory In Chile, they were looking for stars whose measurements of their light (or spectrum) showed low contents of strontium and barium.
They zeroed in on three stars that the Magellan Telescope first observed between 2013 and 2014. They were perfect candidates for the class to study because astronomers hadn’t interpreted their spectra to infer their origins.
Analysis revealed that all three stars had very low levels of strontium and barium, as well as low levels of other elements, including iron, compared to the Sun. One of the stars had less than 10,000 times less iron and helium than the present-day Sun. The rarity of the chemical makeup was a sure hint that the three stars originally formed 12 to 13 billion years ago.
[Related: ‘Homemade’ Telescope Spots Seven Dwarves in Space.]
“Solving this required a lot of staring at computers, lots of debugging, and frantic texting and emailing,” says Ananda Santos, an undergraduate at MIT. It said in a statement“It was a great learning experience and a special one.”
Frebel plans to resume the class this fall semester, and the team hopes to continue discovering similar SASS stars and using them as proxies. Faint dwarf galaxiesThese galaxies are thought to be some of the first surviving galaxies in the Universe – still alive today, but too distant for astronomers to study in detail. SASS’s stars may have once belonged to a similar dwarf galaxy, but are much closer and within our own Milky Way galaxy, which could help astronomers better understand how ultrafaint dwarf galaxies evolve.
“Now, instead of chasing these extremely faint stars, we can look for brighter similar stars in the Milky Way and study their chemical evolution,” Frebel said.
