The Oldest Star In The Universe: Evidence Suggests That Some Early Star Explosions May Not Have Been So Powerful
Perhaps the most basic question in science is this: How did the universe come to be? Scientists in Australia and at MIT believe they've come closer to those first few moments of universal existence in a new study of the oldest star ever observed.
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The star is relatively close to Earth, just 6,000 light years away, and within our own Milky Way galaxy. Previous record holders for oldest star were estimated at 13.2 billion years old. But this star — called SMSS J031300.36-670839.3 — is more like 13.7 billion years old, just slightly younger than the universe itself, the scientists announced in an MIT news release and in The Conversation science blog.
"The telltale sign that the star is so ancient is the complete absence of any detectable level of iron in the spectrum of light emerging from the star," Stefan Keller, one of the study's authors from Australian National University, wrote in The Conversation. That this star contains so little iron is huge for astronomers. Not only does it tell them that the star is old, but it fundamentally changes the perception of what the young universe was like.
To explain, let's consider how most scientists think the universe was formed. The big bang happened perhaps 13.8 billion years ago, when all matter was condensed in a tiny ball that exploded into molten clouds of hydrogen and helium. These clouds collapsed into the first stars. One of the great functions of stars is nuclear fusion; with their extreme heat, they turn light elements into heavier ones. Scientists guess that many of these stars were enormous and short lived. When they died, they exploded, shedding vast new clouds of heavier particles — like iron or oxygen — into space. These clouds collapsed again, and the second generation of the universe's stars were born.
In the present research, the authors believe they've found a second-generation star. It's an astounding discovery, considering Keller estimates there are only perhaps a dozen of these super-ancient stars left. Keller and his colleagues analyzed the spectrum of light emitting from the star. (From this they can learn its contents because each element gives off a signature wavelength.) They determined the star was very high in carbon, but low in iron. They were surprised — most scenarios predict that the first stars died in massive explosions, sending even the deepest, heaviest elements like iron into the void. In this case, the parent star must have only exploded a little, releasing the carbon on its surface but not the iron at its core.
"This star had a lower-than-expected explosion energy, and also lower than today's regular supernovae, which was really an unexpected finding," says co-author Anna Frebel, an assistant professor of physics at MIT. "That tells us that, to some extent, we have to go back to the drawing board, because there is more variety among this very first generation of stars than we have assumed so far." She added that "we've sort of rattled theory a little in a good way to say, 'Maybe we have to rethink how the first stars formed.'"
The scientists involved with the project believe they've come a step closer to understanding our origins. Stars, after all, created the elements that are vital to life. It wasn't an easy project. To find this oldest star, they had to sift through data of more than 60 million known stars, Keller wrote. "This star has born silent witness to 99 percent of the life of the universe," he wrote. "It has spun impervious, slowly converting hydrogen into helium as demanded by gravity."
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