Space + Flight

22
Aug

Rare ‘Pair Instability’ Supernova Buried One of Universe’s Massive Early Stars

Several hundred million years after the Big Bang, clumps of dark matter started to collapse, forming complex mixtures of gases that soon ignited, creating the first stars. These so-called population III stars were only about ten or so solar masses, but for a long time, astronomers have pondered the existence of much bigger early-universe stars, perhaps hundreds of times as massive as the Earth’s sun.

Now, team of Japanese and American scientists has published a paper in which they report the first indirect (but substantiated evidence) of such super-large ancient stars. And it’s buried within another star.

Using a technique called “stellar archaeology,” they analyzed more recent—but still very old—stars that had absorbed the supernova remains of their ancestors. Specifically, they wanted to see if they could find elements leftover from a population III star explosion chemically inscribed in a particular second-generation star 1,000 light-years from Earth: one they dubbed SDSS J0018-0939.

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An artist's depiction of stars forming in the early universe.

Here’s Amina Kahn, writing for the Los Angeles Times:

The researchers found a star they named SDSS J0018-0939 (which, believe it or not, is actually the shortened version of the name). This older-generation star was full of chemical contradictions. For example, it was running unusually low on lighter heavy elements, like carbon and magnesium, but it was also low in cobalt, which doesn’t make sense. A low-carbon signature should mean that the star’s carbon came from a high-energy supernova, while the low-cobalt signature usually implies a “lower explosion energy,” the study authors wrote.

These contradictions could be explained if an older, population III star had undergone a rare, dramatic explosion: a pair-instability supernova.

A pair-instability supernova occurs when pressure in the stellar core is suddenly reduced. That causes the outer layers of the star to collapse inward and results in intense heating and energizing of the core’s gamma-ray photons, turning them into a spew of electron-positron pairs. The increased energy reduces internal pressure even more, and the star dies in what Volker Bromm of the University of Texas in Austin told the LA Times is something akin to a “colossal thermonuclear explosion.”

It’s a significant finding, since previously scientists didn’t think this type of supernova—a hundred times more powerful than the ones we see today—could have occurred in the very early universe. The stars would have been too small to unleash that kind of power. But the new evidence suggests that a few stars might’ve been big enough.

What’s more, knowing these early stars’ mass is important because the information helps cosmologists compose a clearer image of how quickly the universe recovered from its “dark ages”—that is, how quickly stars were formed. Super-large, “pioneer” stars like this one would have had a sizable effect on the overall development of our universe.