Tag Archives: gamma-ray burst

Missing Link Between The Universe’s Most Powerful Explosions Found

Scientists have created a simulation that proves how some of the most powerful explosions in the universe, hypernovae, can be responsible for some of its brightest and most mysteriousevents, gamma ray bursts (GRBs). Incredibly, this is all based on just the first 10 milliseconds (10 millionths of a second) after a massive star collapses.

The research was carried out by scientists at the University of California, Berkeley, and is published in Nature. The process itself involves a rapidly rotating star collapsing. As this happens, it spins faster and faster with its attached magnetic field, producing a dynamo effect that is a million billion times stronger than Earths magnetic field.

A dynamo is a way of taking the small-scale magnetic structures inside a massive star and converting them into larger and larger magnetic structures needed to produce hypernovae and long gamma-ray bursts, said Philipp Msta, a UC Berkeley postdoctoral fellow and first author of the paper, in a statement. People had believed this process could work out. Now we actually show it.

Hypernovae are hypothesized to be extremely powerful supernovae stellar explosions but their cause is not fully understood. In a hypernova, the inner star that is about 930 miles (1,500 kilometers) across collapses into a neutron star about 10 miles (15 kilometers) across, known as a core-collapse supernova.

GRBs, meanwhile, are among the brightest events in the universe, hugely powerful emissions of gamma rays of unknown origin lasting up to 100 seconds, while hypernovae shine more than 10 times brighter than an average supernova.

Crucially, the simulation helps to explain a missing link in connecting hypernovae with GRBs. Scientists had been unsure how a star could amplify a magnetic field not wholly dissimilar to the Suns in terms of powerinto one a quadrillion times more powerful during these explosive events.

This supercomputer visualization shows how a stars rotation can rev up its magnetic field to a million billion times the power of our Suns. UC Berkeley Campus Life

The key appears to be a shear zone 10 to 20 miles (15 to35 kilometers) from the inner star where its different layers are rotating at different speeds, creating a large amount of turbulence that causes the dynamo effect and leads to the hugely amplified magnetic fields. These in turn produce two jets in opposite directions composed of extremely energetic gamma rays, namely gamma ray bursts.

In this simulation, 130,000 computer cores at the Blue Waters supercomputer at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign were used to model the brief fraction of a second after the core collapse, producing the intriguing results.

The breakthrough here is that Philipps team starts from a relatively weak magnetic field and shows it building up to be a very strong and large-scale coherent magnetic field of the kind that is usually assumed to be there when people make models of gamma-ray bursts, said Eliot Quataert, a UC Berkeley professor of astronomy who was not involved with the study, in the statement.

The simulation shows how the dynamo effect causes a feedback loop that can create huge magnetic fields when a massive star collapses, producing both cosmic phenomena. Future simulations from the same team will seek to model more than just 10 milliseconds of a hypernovas evolution to further understand the process taking place.

Read more: http://www.iflscience.com/space/missing-link-between-universes-most-powerful-explosions-found

What Happens When Neutron Stars Collide?

A beautifully elegant visualization of perhaps one of the most ferocious events that can occur in the universe has been released by NASA. This supercomputer simulation, produced by the Albert Einstein Institute, demonstrates what happens when two neutron stars collide and form a black hole.

Neutron stars are one of several possible endings for a star. They form when a huge star, around 8 to 30 times the mass of our Sun, explodes in a supernova. They’re only city size, around 12 miles (20 kilometers) in diameter, but size isn’t everything and they certainly pack a punch with a mass about 1.4 times that of our Sun. To put that into perspective, a cubic centimeter of neutron star matter would weigh more than Mount Everest.

When neutron stars collide a spectacular event ensues. In this simulation, scientists placed a mismatched pair of neutron stars, weighing 1.4 and 1.7 solar masses, 11 miles apart and watched the fateful event play out. As the stars start to whirl toward each other, immense tidal forces warp the crusts of the stars and the smaller star explodes, spewing its hot and dense contents that then begin spiral around the system. As the stars merge, the overwhelming mass acquired by the larger star causes it to collapse, and a black hole is born.

Watch the mesmerizing simulation unfold in full below:

These events are particularly interesting because scientists believe that they may result in short gamma-ray bursts (GRBs). These short GRBs are immense bursts that emit the same amount of energy as all of the stars in our entire galaxy combined produce in a year, in only around 2 seconds. Since these events are over in the blink of an eye observing them in space has proved quite a challenge, but NASA’s Swift mission has been capturing GRB afterglows which has led to a significant increase in our comprehension of these events. 

Read more: http://www.iflscience.com/space/what-happens-when-neutron-stars-collide

Scientists Provide Simple Explanation For Rare Five-Hour Space Explosion

Earlier on this year, an extraordinarily long Gamma Ray Burst sparked a flurry of excitement in the scientific community, prompting several groups to attempt to explain the unusual event. Now, an international team of astronomers, including scientists from Penn State and the University of Leicester, has come up with a new, elegantly simple explanation for these enigmatic events. The work is due to be presented next week in St. Petersburg, Russia.

As the name suggests, Gamma-Ray Bursts (GRBs) are fleeting, intense blasts of gamma-ray light, which is the most energetic form of light. These spectacular explosions are some of the most powerful events in the universe, shining around a million trillion times brighter than the Sun. On average, these violent events occur around once a day, usually lasting from a few milliseconds to several minutes. It was therefore particularly unusual for scientists to observe the energy from one flooding toward Earth for more than five hours.

This rare event, which was named GRB 130925A, is a member of a newly recognized class of GRBs called ultra-long bursts. The explosion was observed using the Swift satellite’s X-ray Telescope and the US/Russian satellite Konus-Wind.

The discovery of these unusual events prompted scientists to wonder whether current theories could adequately explain them, but nonetheless several papers were released on GRB 130925A. Now, according to a new study, the most likely explanation is much simpler than first anticipated.

After examining the observations from Swift and Konus-Wind, the researchers found that these ultra-long gamma-ray bursts are actually standard explosions, but what sets them apart are the conditions in which they arise. According to Penn State professor of astronomy David Burrows, all that is required is for the event to occur within a low-density region located behind a dust cloud when viewed from Earth.

“One reason that these results are satisfying is that scientists generally prefer to find the simplest explanations for mysterious phenomena,” said Burrows

[Via Penn State]

Read more: http://www.iflscience.com/space/scientists-provide-simple-explanation-rare-5-hour-space-explosion