A group of undergraduate students were among those who recently found the oldest known star in the universe, hiding out 80,000 light years from Earth. Though the star now lives in our own Milky Way galaxy, researchers said it is a “galactic immigrant.”
They mean that the ancient star – known as SDSS J0715−7334 – formed somewhere else and then moved to our galaxy. Its makeup includes amounts of heavy metal that exceed the previous oldest star record holder (likely the “Methuselah star” cataloged as HD 140283, according to NASA).
That makes SDSS J0715−7334 “the oldest-known star by a wide margin,” according to a press release from the University of Chicago. A class of undergraduate students from the school journeyed to the Magellan Telescopes at Carnegie Science’s Las Campanas Observatory in the remote mountains of Chile over spring break last year on a star treasure hunt.
At home in the U.S., Alexander Ji, an assistant professor of astronomy and astrophysics, set his students on the hunt for ancient stars by having then comb through star catalogs made by the Sloan Digital Sky Survey. They looked through these catalogs, trying to find anomalous heavy metal readings, and found a handful of “candidate” stars.
“Because it takes time to build up an accumulation of heavy elements, the less of them a star has, the older it must be,” UChicago explained.
While they had the data from the Sloan Digital Star Survey, the powerful telescopes in Chile helped them get more detailed measurements. On the first night they arrived at the observatory, the UChicago students began scanning the skies for the candidate stars they had identified.
“In the early hours of the morning, they got an inkling that something was up,” said the university press release.
Natalie Orrantia, a fourth-year college student, said that teaching assistant Hillary Diane Andales “started making these little noises” as she was doing some preliminary analysis. Andales then spoke up.
“This is nuts, could it be a mistake?” she said, according to Orrantia. As they took a closer look, it became more apparent that what Andales was seeing was real.
Ha Do, another fourth-year student, said “you could feel the energy in the room.”
Still, they wanted to observe more. They allotted hours to observing the star the following night. By the time they were on the flight home, Ji realized that his life had changed.
“I sat there just scrapping and rewriting the entire curriculum I had planned for the next quarter,” he said. “Instead, we were going to throw everything into analyzing this star.”
That’s exactly what they did. Ji’s students divided into small groups to analyze the data they had collected and to write a scientific paper about their findings. It was published this week in the Nature Astronomy journal.
Not only did the team find a new record-holder for earliest known star, they also shed new light on why newer generations of stars grew smaller than the first, UChicago said. Out of two existing theories – that presence of heavy metals made them smaller or that cosmic dust did – the composition of SDSS J0715−7334 indicates one of them is more likely.
“It seems the transition was much more likely caused by that cosmic dust,” said Pierre Thibodeaux, a graduate student at UChicago and co-author on the study.
According to the research team, SDSS J0715−7334 stood out because it is a “chemically pristine” star. It dates back to the early stages of the universe, an estimated several billion years after the big bang 13.8 billion years ago. Our solar system’s own star, the sun, is approximately 4.5 billion years old.
“These pristine stars are windows into the dawn of stars and galaxies in the universe,” said Ji. “I expected great things from the students, but this is above and beyond.”
Stars shining lightyears away from our planet might seem like something that doesn’t have a lot of impact on us humans. However, UChicago explained that the stars of the early universe, made up of just helium and hydrogen, burned hot and died early, leaving atoms to fuse into heavy elements inside their cores and debris that new stars formed from.
“As this happened over and over, we got more heavy elements, until there was enough to make up the iron in our blood and the oxygen we breathe,” said the university.
“So it’s really cool that we found this star, but also, the more you find, the stronger the claims you make about these early stars and how our universe evolved,” Orrantia said.
