Breakthrough study confirms cause of short gamma-ray bursts

Apr 07, 2011
These images show the merger of two neutron stars recently simulated using a new supercomputer model. Redder colors indicate lower densities. Green and white ribbons and lines represent magnetic fields. The orbiting neutron stars rapidly lose energy by emitting gravitational waves and merge after about three orbits, or in less than 8 milliseconds. The merger amplifies and scrambles the merged magnetic field. A black hole forms and the magnetic field becomes more organized, eventually producing structures capable of supporting the jets that power short gamma-ray bursts. Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla

A new supercomputer simulation shows the collision of two neutron stars can naturally produce the magnetic structures thought to power the high-speed particle jets associated with short gamma-ray bursts (GRBs). The study provides the most detailed glimpse of the forces driving some of the universe's most energetic explosions.

The state-of-the-art simulation ran for nearly seven weeks on the Damiana computer cluster at the Institute (AEI) in Potsdam, Germany. It traces events that unfold over 35 milliseconds -- about three times faster than the blink of an eye.

GRBs are among the brightest events known, emitting as much energy in a few seconds as our entire galaxy does in a year. Most of this emission comes in the form of gamma rays, the highest-energy form of light.

"For the first time, we've managed to run the simulation well past the merger and the formation of the black hole," said Chryssa Kouveliotou, a co-author of the study at NASA's Marshall Space Flight Center in Huntsville, Ala. "This is by far the longest simulation of this process, and only on sufficiently long timescales does the magnetic field grow and reorganize itself from a chaotic structure into something resembling a jet."

GRBs longer than two seconds are the most common type and are widely thought to be triggered by the collapse of a massive star into a black hole. As matter falls toward the black hole, some of it forms jets in the opposite direction that move near the speed of light. These jets bore through the collapsing star along its rotational axis and produce a blast of after they emerge. Understanding short GRBs, which fade quickly, proved more elusive. Astronomers had difficulty obtaining precise positions for follow-up studies.

That began to change in 2004, when NASA's began rapidly locating bursts and alerting astronomers where to look.

"For more than two decades, the leading model of short GRBs was the merger of two neutron stars," said co-author Bruno Giacomazzo at the University of Maryland and NASA's Goddard Space Flight Center in Greenbelt, Md. "Only now can we show that the merger of neutron stars actually produces an ultrastrong magnetic field structured like the jets needed for a GRB."

A neutron star is the compressed core left behind when a star weighing less than about 30 times the sun's mass explodes as a supernova. Its matter reaches densities that cannot be reproduced on Earth -- a single spoonful outweighs the Himalayan Mountains.

The simulation began with a pair of magnetized neutron stars orbiting just 11 miles apart. Each star packed 1.5 times the mass of the sun into a sphere just 17 miles across and generated a magnetic field about a trillion times stronger than the sun's.

In 15 milliseconds, the two crashed, merged and transformed into a rapidly spinning black hole weighing 2.9 suns. The edge of the black hole, known as its event horizon, spanned less than six miles. A swirling chaos of superdense matter with temperatures exceeding 18 billion degrees Fahrenheit surrounded the newborn black hole. The merger amplified the strength of the combined magnetic field, but it also scrambled it into disarray.

Over the next 11 milliseconds, gas swirling close to the speed of light continued to amplify the magnetic field, which ultimately became a thousand times stronger than the neutron stars' original fields. At the same time, the field became more organized and gradually formed a pair of outwardly directed funnels along the black hole's rotational axis.

This is exactly the configuration needed to power the jets of ultrafast particles that produce a short . Neither of the magnetic funnels was filled with high-speed matter when the simulation ended, but earlier studies have shown that jet formation can occur under these conditions.

"By solving Einstein's relativity equations as never before and letting nature take its course, we've lifted the veil on short GRBs and revealed what could be their central engine," said Luciano Rezzolla, the study's lead author at AEI. "This is a long-awaited result. Now it appears that neutron star mergers inevitably produce aligned jet-like structures in an ultrastrong magnetic field."

Explore further: The Great Debate over whether the universe is small or large

More information: The study is available online and will appear in the May 1 edition of The Astrophysical Journal Letters.

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omatumr
1 / 5 (9) Apr 07, 2011
Thank you, thank you, for another great news report on the important role of neutron stars in explaining the cosmos that we observe.

I hope that others will take the time to study nuclear rest mass data and the predictions they make for energetic neutron stars!

"The Sun is a plasma diffuser that sorts atoms by mass",
Physics of Atomic Nuclei 69, 1847-1856 (2006)
http://arxiv.org/.../0609509

Again - thanks,
Oliver K. Manuel

kaasinees
1 / 5 (1) Apr 07, 2011
omar tumor

nuf sad
Shelgeyr
1.5 / 5 (8) Apr 08, 2011
Who writes the headlines for these works of fiction? This "breakthrough study" doesn't CONFIRM a darn thing.

I mourn for the state of science these days. Go ahead and look to models for guidance here and there, but the results of models are NOT evidence supporting a hypothesis, so claiming they confirm something is outright false.

They're lucky I don't hold the funding purse-strings... my detailed political science and actuarial models confirm that I'd strip all public funding from any researcher who dared make such a claim, ban them for life from research, send them into exile, and (lightly) kick their dog just to emphasize the point.
Ethelred
4.3 / 5 (6) Apr 08, 2011
Do you think neutron repulsion is a long range force or a short ranges force? What distinguishes it from the Pauli Exclusion Principle?

Please note that on most of the other sites that allow alternate to mainstream theory the theorist is REQUIRED to answer questions and to NOT spam the site. Which I think is much better than simply disallowing alternate theory. However you refuse to answer legitimate questions and you are spamming this site. Must be one of the few you have yet to be banned from.

So how about you answer the question.

Ethelred
soulman
3.7 / 5 (6) Apr 08, 2011
on most of the other sites that allow alternate to mainstream theory the theorist is REQUIRED to answer questions and to NOT spam the site.

Yeah, I'm familiar with the baut board's Against The Mainstream forum, which adheres strictly to that rule. I love going there just to see the cranks get a roasting by members with a solid knowledge of physics and science in general, some who are practicing physicists. Oliver wouldn't last a second there.
omatumr
Apr 10, 2011
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