What started as a class assignment turned into one of the most extraordinary astronomical discoveries in recent memory. A group of undergraduate students at the University of Chicago, working through massive telescope datasets as part of a course project, stumbled upon a star so ancient and chemically pure that it appears to be a direct relic from the very dawn of the universe — and it didn’t even originate in our galaxy.

A Class Project That Became a Cosmic Breakthrough

The ten students were enrolled in the university’s “Field Course in Astrophysics,” led by Professor Alex Ji, who also serves as deputy Project Scientist for the Sloan Digital Sky Survey (SDSS). Working alongside graduate teaching assistants Hillary Andales and Pierre Thibodeaux, the students spent several weeks combing through SDSS datasets — one of the most comprehensive astronomy data collections on the planet, built over 25 years by more than 75 scientific institutions worldwide.

From thousands of stars examined, the class narrowed their list to 77 promising candidates for closer observation. They then packed their bags for Carnegie Science’s Las Campanas Observatory in Chile — a Spring Break trip that would change the course of their academic careers.

The Second Star of the Night Stopped Everything

The team’s first observing session took place on March 21, 2025, using the Magellan Inamori Kyocera Echelle instrument on the Magellan telescopes. The plan was straightforward: observe each target star for roughly 10 minutes and move on. That plan lasted until the second star of the night.

The object — catalogued as SDSS J0715-7334 — was immediately unlike anything else on their list. The students and their professor quickly recognised they were looking at something extraordinary.

“We found it the first night, and it completely changed our plans for the course.”

— Professor Alex Ji, University of Chicago

The following night, instead of the planned 10-minute observation, the team spent three full hours studying the star. Student Natalie Orrantia kept watch over the camera the entire time, unwilling to miss a moment of the data collection.

Why This Star Is Unlike Anything Ever Seen Before

SDSS J0715-7334 is composed almost entirely of hydrogen and helium — the two elements that existed at the very beginning of the universe, before stars began forging heavier elements through nuclear fusion and scattering them across space through supernova explosions. In astronomical terms, the star has “metallicity” — the proportion of elements heavier than hydrogen and helium — of just 0.005% of what is found in our own Sun.

That makes it the most metal-poor star ever recorded, more than twice as metal-poor as the previous record holder. A star this chemically pristine must have formed before most of the universe’s supernovae had a chance to enrich the interstellar medium with heavier elements — placing its birth in the very earliest generations of star formation, billions of years ago.

“We analyzed the star for a large swath of elements, and the abundances are quite low for all of them.”

— Ha Do, student researcher

It Came From Another Galaxy — and Migrated Into the Milky Way

The story gets even more remarkable. By combining their telescope observations with orbital data from the European Space Agency’s Gaia mission, the team was able to trace the star’s path through space backwards over billions of years. What they found was that SDSS J0715-7334 did not form in the Milky Way at all — it originated in the Large Magellanic Cloud, the Milky Way’s largest companion galaxy, before being gravitationally pulled into our galaxy long ago.

Professor Ji gave it a fitting nickname: the “Ancient Immigrant.” It is a star born in another galaxy, in the earliest epoch of cosmic history, that has been quietly drifting through our own galaxy ever since.

“This ancient immigrant gives us an unprecedented look at conditions in the early universe. Big data projects like SDSS make it possible for students to get directly involved in these important discoveries.”

— Professor Alex Ji

A Rare Chemical Signature Points to an Unusual Formation Pathway

One more surprise was waiting in the data. When students analysed the star’s carbon content, they found so little of it that it couldn’t even be detected — a chemical signature so unusual that it points to a specific and extremely rare formation process involving early cosmic dust. According to Ji, this particular formation pathway has only been observed once before in the history of astronomy.

For the Students Who Found It, Everything Has Changed

Both Natalie Orrantia and Ha Do have announced plans to pursue graduate studies in astronomy following the discovery — a direct result of experiencing what it feels like to genuinely contribute to human knowledge at the frontier of science.

“To be able to actually contribute to something like this — it’s very exciting.”

— Ha Do, student researcher

Juna Kollmeier, Director of SDSS-V, perhaps captured the moment best. The students, she said, had discovered more than just the most pristine star ever found. They had discovered something about themselves — and proved that with the right tools and the right questions, some of the universe’s deepest secrets are still out there waiting to be found by anyone willing to look.