These images show the merger of two neutron stars (yellow) 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.
Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla
The merger amplifies and scrambles the merged magnetic field. A black hole forms at 15.3 milliseconds.
Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla
The magnetic field becomes more organised at 26.5 milliseconds, eventually producing structures capable of supporting the jets that power short gamma-ray bursts.
Credit: NASA/AEI/ZIB/M. Koppitz and L. Rezzolla
WASHINGTON: A new supercomputer simulation has shown the most detailed glimpse of the forces driving some of the universe's most energetic explosions - short gamma-ray bursts (GRBs).
The state-of-the-art simulation traced the collision of two neutron stars that naturally produce the magnetic structures thought to power the high-speed particle jets associated with GRBs. The events unfolded over 35 milliseconds - about three times faster than the blink of an eye.
"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 Centre in Huntsville, Alabama.
"This is by far the longest simulation of this process, and only on sufficiently long timescales does the magnetic field grow and reorganise itself from a chaotic structure into something resembling a jet."
Understanding the elusive GRBs
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.
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 gamma rays after they emerge. Understanding short GRBs, which fade quickly, proved more elusive. Astronomers had difficulty obtaining precise positions for follow-up studies.
Rethinking the model
That began to change in 2004, when NASA’s Swift satellite 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 Centre in Greenbelt, Maryland.
"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."
