A group of students from the University of Chicago has made an incredible discovery: an ultra-ancient star, SDSS J0715-7334, that shouldn’t be in the Milky Way. This one, almost devoid of heavy elements, formed in another galaxy before drifting into our own.
The discovery was made by a team of students under the guidance of Professor Alex Ji, using data from the Sloan Digital Sky Survey (SDSS). This international collaboration gathers astronomical data to help scientists study the evolution of stars, black holes, and galaxies.
They Found A Cosmic Fossil Star
It all started in an astronomy class at the University of Chicago. As reported by the Professor Alex Ji, the students were tasked with examining thousands of stars using SDSS data. On their first night of observation, one of the objects stood out immediately.
“We found it the first night, and it completely changed our plans for the course,” Ji said.
SDSS J0715-7334, a red giant star, travels from the Large Magellanic Cloud to the Milky Way. Credit: Carnegie Institution for Science
The finding in question, SDSS J0715-7334, has unique characteristics: it’s mostly made up of hydrogen and helium, with almost no metals, making it one of the oldest and most “pristine” stars ever observed. The lack of heavy elements like carbon or oxygen indicates that this star formed long before most supernovae, which are responsible for creating heavier elements.
“All of the heavier elements in the universe, which astronomers call metals, were produced by stellar processes—from fusion reactions occurring within stars to supernovae explosions to collisions between very dense stars,” added Ji in a statement released by the Carnegie Institution for Science. “So, finding a star with very little metal content in it told this group of students that they’d come across something very special.”
An “Immigrant” Star from Another Galaxy
SDSS J0715-7334 didn’t come from the Milky Way. Instead, it originated in the Large Magellanic Cloud, a neighboring galaxy. By tracing its movement through space, the researchers discovered that it left its galaxy of origin and eventually drifted into the Milky Way billions of years ago.
This intergalactic journey earned the celestial body the title of “ancient immigrant,” according to Professor Ji.
“This ancient immigrant gives us an unprecedented look at conditions in the early universe,” he said. “Big data projects like SDSS make it possible for students to get directly involved in these important discoveries.”
Students at the Forefront of Discovery
What’s particularly remarkable about this discovery, detailed in Nature Astronomy, is that it was driven by students. Ha Do, one of the students on the project, shared the excitement:
“To be able to actually contribute to something like this, it’s very exciting.” The student involvement in this work highlights how collaborative projects like SDSS offer young researchers access to advanced astronomical data.
This image shows the orbit of SDSS J0715-7334, tracing its path from the Large Magellanic Cloud (LMC) into the Milky Way. Credit: Nature Astronomy
Natalie Orrantia, another member of the team, plans to pursue graduate studies because of this experience. As Juna Kollmeier, Director of SDSS-V, put it:
“When I was an undergraduate, I greatly preferred doing research to taking classes. I’m delighted that Alex’s course was transformed into a curriculum of discovery and I’d like to ensure surveys like SDSS-V and Gaia have the power to make that the norm and not the exception,” she noted. “These students have discovered more than just the most pristine star; they have discovered their inalienable right to physics.”