A small galaxy circling the Milky Way could be leftovers from the universe's earliest days.
The galaxy, dubbed Segue 1, contains fewer heavy than any other known galaxy, Scientific American reported. This could mean the galaxy evolved as far back as 13 billion years ago.
The galaxy contains only a few hundred stars, which is miniscule when compared to the hundreds of billions that exist in the Milky Way. Some of Segue 1's brightest stars are believed to be made up of only hydrogen and helium, and not heavier elements such as iron. This composition would make Segue 1 the "least chemically evolved galaxy known," Scientific American reported.
Complex metals are often stored in the cores of stars and are transformed into even more complex elements when the stars explode.
"Segue 1 is so ridiculously metal-poor that we suspect at least a couple of the stars are direct descendants of the first stars ever to blow up in the Universe," study co-author Evan Kirby of the University of California, Irvine, told Scientific American.
"Segue 1 is the only example that we know of now that was never enriched by these low-mass stars, meaning it formed stars really quickly, in the blink of an eye," he said. "If it had formed stars long enough those low-mass stars would have to contribute."
These findings suggest the galaxy had a brief period of rapid star formation in the early days of the universe.
"The big question is, why did it stop?" Irvine astrophysicist James Bullock, who did not participate in the study, told Scientific American. "A galaxy like this should have been able to make a million more stars, but it didn't."
Something called reionization could explain the phenomenon. The early was hot, dense, and full of ionized gas; this kept protons and electrons from forming atoms. At some point the universe cooled down enough to allow atoms to form, which is when some of the first stars are believed to have been born.
"Maybe Segue 1 was on its way to forming a bunch of stars but reionization turned on and killed all the star formation in the galaxy," Kirby said. "That could also explain why the star formation lasted such a short time."
"It's not obvious to me that reionization by itself could have done this," Bullock said. "Maybe, but I definitely think there are other possibilities." For instance, perhaps some quirk has caused Segue 1 to be incredibly inefficient at forming stars compared with other galaxies.
