The recent detection of a gamma-ray burst from a massive blue supergiant is helping astronomers understand how the universe's primordial stars ended their lives in cataclysmic explosions. But more than this, it revealed several features never seen before in a stellar explosion.

Astronomers recently detected an anomalous flash of energetic radiation streaming away from a galaxy located 3.9 billion light-years away. Further analysis of the "peculiar event" shows it was a gamma-ray burst with some very strange qualities; it had a freakishly long duration of about 20,000 seconds (that's up to a hundred times the length of a "normal" gamma-ray burst), and it exhibited features not seen before in a gamma-ray burst — a hot cocoon of gas emitting X-ray radiation and a strangely thin wind.

The burst came from a blue supergiant. These stars can reach upwards of several hundred times the mass of the Sun. They're quite rare in the nearby universe, but they were common in the early universe; almost all of the very first stars evolved into them over the course of their short lives.


But unlike other blue supergiants, this one contained very little in the way of elements heavier than hydrogen and helium. The same thing can be said for the first stars to appear in the universe. This means that this gamma-ray burst, dubbed GRB130925A, offers astronomers a remarkable glimpse into what similar explosions must have looked like a mere hundred million years or so after the Big Bang.

The astronomers speculate that the blue star's massive bulk fuelled the ultralong gamma-ray burst. The ESA explains more:


After the Big Bang, the Universe was dominated by hydrogen and helium and therefore the first stars that formed were very metal-poor. However, these first stars made heavier elements via nuclear fusion and scattered them throughout space as they evolved and exploded.

This process continued as each new generation of stars formed, and thus stars in the nearby Universe are comparatively metal-rich.

Finding GRB130925A's progenitor to be a metal-poor blue supergiant is significant, offering the chance to explore an analogue of one of those very first stars at close quarters. Dr [Luigi] Piro [of the Istituto Astrofisica e Planetologia Spaziali in Rome] and his colleagues speculate that it might have formed out of a pocket of primordial gas that somehow survived unaltered for billions of years.

"The quest to understand the first stars that formed in the Universe some 13 billion years ago is one of the great challenges of modern astrophysics," notes Dr Piro. "Detecting one of these stars directly is beyond the reach of any present or future observatory due to the immense distances involved. But it should ultimately be possible to find them as they explode at the end of their lives, producing powerful flashes of radiation."

Read more at the ESA. And check out the entire study at The Astrophysical Journal Letters: "A Hot Cocoon in the Ultralong GRB 130925A: Hints of a PopIII-like Progenitor in a Low Density Wind Environment".

Image: NASA/Swift/A. Simonnet, Sonoma State Univ.

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