“These stars formed before the Milky Way, and the galaxy formed around them,” Louise Howes, a doctoral student from the Australian National University and lead author of a study announcing the stars’ discovery, said in a statement.
Howes’s work, which also involved collaborators from the University of Cambridge, was published Wednesday in the scientific journal Nature. She and her fellow researchers set out to find stars poor in the elements that formed as the universe aged. Once upon a time, cosmic cooks had fewer ingredients to work with; the universe was mostly just hydrogen and helium, with a little lithium thrown into the mix.
As this first generation of mostly-hydrogen stars died, their life-cycles produced new elements for future stars to take on. Scientists are always trying to better understand this evolutionary process, and finding the first stars will help them trace the changes our universe has seen over the past 13.8 billion years.
The researchers found 23 stars in the bulge of the Milky Way that were metal-poor enough to warrant further study. Nine of those stars turned out to have metal contents less than one-thousandth the amount seen in the sun. The most metal-poor star of them all had a record-breaking one ten-thousandth of the metal content of our sun.
The true first stars would have formed as much as 100 million years earlier than the ones featured in the study, based on previous research. In fact, the newly discovered stars show evidence of being second generation — they contain even less carbon and iron than astronomers expected to find, suggesting that they may have formed from material left over from a massive star explosion called a hypernova. The researchers say this could indicate that all early stars went out this way — in explosions 10 times as powerful as more typical supernovae.
“This work confirms that there are ancient stars in the centre of our Galaxy,” study co-author Andrew Casey of Cambridge’s Institute of Astronomy said in a statement. “The chemical signature imprinted on those stars tells us about an epoch in the Universe that's otherwise completely inaccessible.”
Because the center of the Milky Way, which is probably where the true first stars would be found, is full of so many metal-rich stars, finding the old-timers is similar to looking for a needle in a haystack, to say the least. But the latest study is an indication that astronomers may finally have the right needle-finding tools to get the job done.
“The Universe was probably very different early on, but to know by how much, we’ve really just got to find more of these stars: more needles in bigger haystacks,” Casey said.