Observatory sheds light on last acts of first stars

XMM-Newton observatory has helped scientists to discover how the Universe's first stars ended their lives in giant explosions from the recent detection of a gamma-ray burst from a massive blue supergiant.

GRB 130925A, by contrast, produced gamma rays for 1.9 hours, more than a hundred times greater than a typical long GRB. Observations by Swift's XRT revealed an intense and highly variable X-ray afterglow that exhibited strong flares for six hours, after which it finally began the steady fadeout usually seen in long GRBs.

Ultra-long GRBs last hundreds of times longer; the source star must have a correspondingly greater physical size. The most likely suspect, astronomers say, was a blue supergiant, a hot star with about 20 times the Sun's mass that retains its deep hydrogen atmosphere, making it roughly 100 times the Sun's diameter.

Scientist Luigi Piro, the director of research at the Institute for Space Astrophysics said that one of the great challenges of modern astrophysics has been the quest to identify the first generation of stars to form in the universe, which they refer to as Population III stars.

He further added that this was the first time that they have detected this thermal cocoon component, likely because all other known ultra-long bursts occurred at greater distances.

The astronomers concluded that the best explanation for the unusual properties of GRB 130925A was that it heralded the death of a metal-poor blue supergiant, a model they suggested likely characterizes the entire ultra-long class.

Astronomers think Population III stars ended their lives as blue supergiants, so GRB 130925A might prove to be a valuable nearby analog to phenomena they might one day detect from the universe's most distant stars.