A remarkable discovery was made by a group of ten students participating in a "Field Course in Astrophysics" at their university, guided by Professor Alex Ji, who serves as the deputy Project Scientist for SDSS-V, along with graduate teaching assistants Hillary Andales and Pierre Thibodeaux.
Harnessing Big Data for Groundbreaking Discoveries
The Sloan Digital Sky Survey (SDSS) is a collaborative initiative involving over 75 scientific institutions, dedicated to making vast astronomical datasets accessible to both researchers and students. Operating for 25 years, the project utilizes robotic instruments to gather spectra from millions of celestial objects, enabling the study of stellar, black hole, and galaxy evolution.
In Ji's class, students engaged directly with SDSS data, analyzing thousands of stars from the latest survey. They identified 77 candidates for detailed examination during a planned observational trip.
A Transformative Spring Break Expedition
The students traveled to Carnegie Science's Las Campanas Observatory in Chile during Spring Break, utilizing the Magellan Inamori Kyocera Echelle (MIKE) instrument on the Magellan telescopes. Their first observing session occurred on March 21, 2025. The second star they focused on that evening, designated SDSSJ0715-7334, quickly captured their attention.
"We discovered it on the first night, which completely altered our course plans," Ji remarked.
Initially, the plan was to observe each target for about 10 minutes. However, upon recognizing the uniqueness of this star, the students dedicated three hours to its study the following evening.
"I was monitoring that camera all night to ensure it was functioning properly," shared Natalie Orrantia, one of the students involved.
An "Ancient Immigrant" Star from Beyond
This star exhibited an extraordinary composition, predominantly consisting of hydrogen and helium, indicating its formation in the early universe and marking it as one of the oldest stars ever recorded.
Analysis revealed that it did not originate in the Milky Way but was born in the Large Magellanic Cloud, our galaxy's largest companion, before migrating billions of years ago. Ji aptly referred to it as an "ancient immigrant."
"This ancient immigrant provides an unparalleled glimpse into conditions during the universe's infancy," Ji noted. "Projects like SDSS empower students to actively participate in significant discoveries."
Unprecedented Metallicity and Early Cosmic Insights
Astronomers refer to any elements heavier than hydrogen and helium as "metals." The star SDSSJ0715-7334 has a metallicity of just 0.005 percent compared to the Sun, making it the most metal-poor star ever identified, surpassing the previous record holder.
"We assessed a wide range of elements, and their abundances were remarkably low," stated Ha Do, another student on the team.
This low metallicity is a crucial indicator of age, suggesting the star formed before the majority of supernovae occurred, placing it among the universe's earliest stellar generations.
Tracing Its Galactic Journey
To further understand the star's history, the team integrated their observations with data from the European Space Agency's Gaia mission, allowing them to determine its distance and trajectory through the Milky Way.
By retracing its journey over billions of years, they confirmed its origin in the Large Magellanic Cloud before being drawn into the Milky Way.
Unique Chemical Signatures and Future Aspirations
Further investigations revealed another intriguing aspect. Ji divided the class into groups to analyze different characteristics of the star. Orrantia and Do led the team studying its carbon content, which proved so minimal that it was undetectable.
"The star's low carbon suggests an early infusion of cosmic dust in its formation," Ji explained. "This formation pathway has been observed only once before."
Participating in this significant discovery has inspired the students to pursue careers in astronomy. Both Orrantia and Do now plan to continue their studies in this field.
"Contributing to something of this magnitude is incredibly exciting," Do expressed.
"These students have uncovered more than just an exceptional star," stated Juna Kollmeier, Director of SDSS-V. "They have discovered their innate right to engage with physics. Initiatives like SDSS and Gaia open doors for learners everywhere, demonstrating that opportunities for discovery are boundless."