Cosmology studies suggest that the first stars did not appear until 100 million years after the Big Bang. Scientists have recently discovered stars at the center of the galaxy that they believe are not only more ancient than the approximately 13.2-billion-year-old Milky Way, but may be among the oldest objects ever discovered. 

Documented in a Nature article published earlier this week, the discovery was made by a team of astronomers using the Australian National University SkyMapper telescope. The team included ANU Ph.D. student Louise Howes, who explains in the video above that the lack of metals in the atmosphere of the stars is one reason they suspect the stars are very old. The early universe was composed of hydrogen, helium, and small amounts of lithium; all other elements were created later in the supernova explosions of stars.

"We expected them to be lacking in metals, but we also found that they were lacking in elements such as carbon and magnesium," Howes says. Those elements would have come from "pollution" caused by older exploded stars. Because these stars lack those elements, they appear to be quite ancient. "The relatively small stars, for some reason, had 10 times the amount of energy that we would expect, and exploded in what we call a 'hypernova,'" she said. The hypernova would have released a lot of other elements, like iron and nickel, but not much carbon or magnesium.

Their proximity to the center of the galaxy was another clue, because it's thought the first stars formed at the galaxy center, where the effects of gravity are the strongest. 

"The chemical signature imprinted on those stars tells us about an epoch in the universe that's otherwise completely inaccessible," said study co-author Andrew Casey, of Cambridge University's Institute of Astronomy, in a press statement. "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."