Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Out of An Hours-long Explosion, A Stand-In For The First Stars

14.07.2014

Astronomers analyzing a long-lasting blast of high-energy light observed in 2013 report finding features strikingly similar to those expected from an explosion from the universe's earliest stars. If this interpretation is correct, the outburst validates ideas about a recently identified class of gamma-ray burst and serves as a stand-in for what future observatories may see as the last acts of the 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," explained lead scientist Luigi Piro, the director of research at the Institute for Space Astrophysics and Planetology in Rome, a division of Italy's National Institute for Astrophysics (INAF). "This important event takes us one step closer."


In this artist's rendering of GRB 130925A, a sheath of hot, X-ray-emitting gas (red) surrounds a particle jet (white) blasting through the star's surface at nearly the speed of light. The source may have been a metal-poor blue supergiant, an important proxy for the universe's first stars.

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

Gamma-ray bursts (GRBs) are the most luminous explosions in the universe. The blasts emit outbursts of gamma rays -- the most powerful form of light -- and X-rays, and produce rapidly fading afterglows that can be observed in visible light, infrared and radio wavelengths. On average, NASA's Swift satellite, Fermi Gamma-ray Space Telescope and other spacecraft detect about one GRB each day.

Shortly after 12:11 a.m. EDT on Sept. 25, 2013, Swift's Burst Alert Telescope triggered on a spike of gamma rays from a source in the constellation Fornax. The spacecraft automatically alerted observatories around the world that a new burst -- designated GRB 130925A, after the date -- was in progress and turned its X-ray Telescope (XRT) toward the source. Other satellites also detected the rising tide of high-energy radiation, including Fermi, the Russian Konus instrument onboard NASA's Wind spacecraft, and the European Space Agency's (ESA) INTEGRAL observatory.

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.

Astronomers have observed thousands of GRBs over the past five decades. Until recently, they were classified into two groups, short and long, based on the duration of the gamma-ray signal. Short bursts, lasting only two seconds or less, are thought to represent a merger of compact objects in a binary system, with the most likely suspects being neutron stars and black holes. Long GRBs may last anywhere from several seconds to several minutes, with typical durations between 20 and 50 seconds. These events are thought to be associated with the collapse of a star many times the sun's mass and the resulting birth of a new black hole.

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.

"GRB 130925A is a member of a rare and newly recognized class we call ultra-long bursts," said Eleonora Troja, a visiting research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a member of the study team. "But what really sets it apart is its unusual X-ray afterglow, which provides the strongest case yet that ultra-long GRBs come from stars called blue supergiants."

Astronomers think Wolf-Rayet stars best explain the origin of long GRBs. Born with more than 25 times the sun's mass, these stars burn so hot that they drive away their outer hydrogen envelopes through an outflow called a stellar wind. By the time it collapses, the star's outer atmosphere is essentially gone and its physical size is comparable to the sun's. A black hole forms in the star's core and matter falling toward it powers jets that burrow through the star. The jets continue operating for a few tens of seconds -- the time scale of long GRBs.

Because ultra-long GRBs last hundreds of times longer, the source star must have a correspondingly greater physical size. The most likely suspect, astronomers say, is 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. Better yet, blue supergiants containing only a very small fraction of elements heavier than helium -- metals, in astronomical parlance -- could be substantially larger. A star's metal content controls the strength of its stellar wind, and this in turn determines how much of its hydrogen atmosphere it retains before collapse. For the largest blue supergiants, the hydrogen envelope would take hours to fall into the black hole, providing a sustained fuel source to power ultra-long GRBs.

Writing in the July 10 edition of The Astrophysical Journal Letters, the researchers note that radio observations of the GRB afterglow show that it displayed nearly constant brightness over a period of four months. This extremely slow decline suggests that the explosion's blast wave was moving essentially unimpeded through space, which means that the environment around the star is largely free of material cast off by a stellar wind.

The burst's long-lived X-ray flaring proved a more puzzling feature to explain, requiring observations from Swift, NASA's Chandra X-ray Observatory and ESA's XMM-Newton satellite to sort out. As the high-energy jet bores through the collapsing star, its leading edge rams into cooler stellar gas and heats it. This gas flows down the sides of the jet, surrounding it in a hot X-ray-emitting sheath. Because the jet travels a greater distance through a blue supergiant, this cocoon becomes much more massive than is possible in a Wolf-Rayet star. While the cocoon should expand rapidly as it exits the star, the X-ray evidence indicates that it remained intact. The science team suggests that magnetic fields may have suppressed the flow of hot gas across the cocoon, keeping it confined close to the jet.   

"This is the first time we have detected this thermal cocoon component, likely because all other known ultra-long bursts occurred at greater distances," said Piro.

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

Stars make heavy elements throughout their energy-producing lives and during their death throes in supernova explosions and GRBs. Each generation enriches interstellar gas with a greater proportion of metals, but the process is not uniform and metal-poor galaxies still exist nearby. Looking farther into the universe means looking deeper into the past, toward earlier stellar generations formed out of increasingly metal-poor gas. Astronomers think Population III stars ended their lives as blue supergiants, so GRB 130925A may prove to be a valuable nearby analog to phenomena we may one day detect from the universe's most distant stars.

Francis Reddy
NASA's Goddard Space Flight Center

Francis Reddy | Eurek Alert!
Further information:
http://www.nasa.gov/content/goddard/out-of-an-hours-long-explosion-a-stand-in-for-the-first-stars/

Further reports about: Astronomers Fermi Flight GRB NASA Telescope X-ray afterglow atmosphere cocoon death explosions spacecraft

More articles from Physics and Astronomy:

nachricht Tiny Drops of Early Universe 'Perfect' Fluid
02.09.2015 | Brookhaven National Laboratory

nachricht Cosmic recycling
02.09.2015 | European Southern Observatory ESO

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Fraunhofer ISE Develops Highly Compact Inverter for Uninterruptible Power Supplies

Silicon Carbide Components Enable Efficiency of 98.7 percent

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE have developed a highly compact and efficient inverter for use in uninterruptible power...

Im Focus: How wind sculpted Earth's largest dust deposit

China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from University of Arizona geoscientists. The study is the first to explain how the steep-fronted plateau formed.

China's Loess Plateau was formed by wind alternately depositing dust or removing dust over the last 2.6 million years, according to a new report from...

Im Focus: An engineered surface unsticks sticky water droplets

The leaves of the lotus flower, and other natural surfaces that repel water and dirt, have been the model for many types of engineered liquid-repelling surfaces. As slippery as these surfaces are, however, tiny water droplets still stick to them. Now, Penn State researchers have developed nano/micro-textured, highly slippery surfaces able to outperform these naturally inspired coatings, particularly when the water is a vapor or tiny droplets.

Enhancing the mobility of liquid droplets on rough surfaces could improve condensation heat transfer for power-plant heat exchangers, create more efficient...

Im Focus: Increasingly severe disturbances weaken world's temperate forests

Longer, more severe, and hotter droughts and a myriad of other threats, including diseases and more extensive and severe wildfires, are threatening to transform some of the world's temperate forests, a new study published in Science has found. Without informed management, some forests could convert to shrublands or grasslands within the coming decades.

"While we have been trying to manage for resilience of 20th century conditions, we realize now that we must prepare for transformations and attempt to ease...

Im Focus: OU astrophysicist and collaborators find supermassive black holes in quasar nearest Earth

A University of Oklahoma astrophysicist and his Chinese collaborator have found two supermassive black holes in Markarian 231, the nearest quasar to Earth, using observations from NASA's Hubble Space Telescope.

The discovery of two supermassive black holes--one larger one and a second, smaller one--are evidence of a binary black hole and suggests that supermassive...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Together - Work - Experience

03.09.2015 | Event News

Networking conference in Heidelberg for outstanding mathematicians and computer scientists

20.08.2015 | Event News

Scientists meet in Münster for the world’s largest Chitin und Chitosan Conference

20.08.2015 | Event News

 
Latest News

Lighter with Laser Welding

03.09.2015 | Process Engineering

For 2-D boron, it's all about that base

03.09.2015 | Materials Sciences

Phagraphene, a 'relative' of graphene, discovered

03.09.2015 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>