July 13, 2014
Unusual Gamma-Ray Burst Found To Mimic Composition Of Ancient Stars
redOrbit Staff & Wire Reports - Your Universe Online
A long-lasting gamma-ray burst that was first observed last year contained traits similar to those expected from explosions of some of the earliest stars in the universe, claims a new study appearing in The Astrophysical Journal.
According to the ESA, the long-lasting blast of extremely energetic radiation was identified as GRB130925A, and thanks to both ground- and space-based equipment, astronomers were able to track its origin to a massive blue supergiant.
While this type of star is said to be rare in the relatively close universe where the gamma-ray burst is located, they are believed to have been quite common in the early universe. However, unlike nearby blue supergiants, GRB130925A's progenitor star contained few elements heavier than hydrogen or helium.
The ESA explained that this was also true for the first stars to form in the universe, which means that GRB130925A is remarkably similar to explosions that occurred only a few hundred million years after the Big Bang.
If the international team of researchers behind this new paper have interpreted their findings correctly, it means that GRB130925A provides evidence supporting a recently-identified class of gamma-ray bursts, and also serves as a potential model for what astronomers may someday witness to be the final acts of the very first stars.
“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 we refer to as Population III stars,” lead author Dr. Luigi Piro of the Institute for Space Astrophysics and Planetology in Rome explained in a statement. “This important event takes us one step closer.”
“There have been several theoretical studies predicting what a gamma-ray burst produced by a primordial star would look like,” he added. “With our discovery, we've shown that these predictions are likely to be correct.”
According to NASA, gamma-ray bursts are not an unusual event, and the Swift satellite, Fermi Gamma-ray Space Telescope and other spacecraft detect roughly one of these luminous explosions each day. However, shortly after 12:11am EDT on September 25, 2013, Swift's Burst Alert Telescope detected a gamma-ray spike originating from a source in the constellation Fornax that wound up being GRB130925A.
“The burst was eventually localized to a galaxy so far away that its light had been traveling for 3.9 billion years, longer than the oldest evidence for life on Earth,” the US space agency said. Until recently, these bursts were divided into two categories based on their lifespan – short (two seconds or less) or long (up to several minutes). GRB130925A wound up lasting over 100 times longer than a typical long gamma-ray burst, boasting a duration of 1.9 hours.
In addition, the ESA said the new gamma-ray burst had a second unique feature – a cocoon of hot gas that emitted X-rays and a strangely thin wind. Based on both this phenomena and the fact that the burst was categorized as an ultra-long one, scientists were able to identify the stellar progenitor as a blue supergiant. They also discovered information about the proportion of the star composed of “metals,” or elements other than hydrogen and helium.
The researchers explain that the majority of the first stars formed following the Big Bang were metal-poor, since there was an abundance of hydrogen and helium in the universe during this time. However, those early stars created heavier elements through nuclear fusion, and those elements were scattered throughout space as those stars evolved and exploded – a process than continued through each new stellar generation, the ESA explained.
As a result, stars formed in the nearby universe tend to be relatively rich in metal when compared to their predecessors. Since GRB130925A's progenitor was identified as a metal-poor blue supergiant, the study authors speculate that it could have formed from a pocket of primordial gas that inexplicably managed to survive unaltered for several billion 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,” said 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.”
Image 2 (below): Artist's impression of a gamma-ray burst, a flash of very energetic radiation associated with a distance galaxy. Credit: ESA, illustration by ESA/ECF
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