Supernova Unlocks Gamma Ray Missing Link

New link found between supernovas that produce gamma rays and those that do not.

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Left: core-collapse supernova with no central engine. Middle: intermediate supernova with weak central engine. Right: strong central engine generating a gamma-ray burst.
CREDIT: Bill Saxton, NRAO/AUI/NSF

The long-sought for connection between supernova explosions that generate gamma-ray bursts (GRB) and those that don't has finally been discovered. It was thought that so called 'engine-driven' supernovas produced gamma rays, but observations of a supernova, observed in 2012 with the National Science Foundation’s Very Large Array telescope, shows this is not the case.

Scientists studying Supernova 2012ap observed that it displays certain characteristics of the type that produces gamma rays, yet no burst has ever occurred.

The research claims to have uncovered a “missing link” between supernovas that produce GRBs and those that do not.

Supernova 2012ap is a core-collapse supernova, which is formed when a large star collapses due to a lack of energy supplied by the nuclear fusion reactions at its core. When this happens to a star, it becomes either a neutron star or a black hole, while its remaining elements are blasted into space by the explosion.

In the most common of these occurrences, the star’s material is flung outward in an expanding spherical shape and produces no gamma rays.

Sometimes, however, as the star begins to collapse, the material is drawn into a swirling disk around the neutron star or black hole. Jets of star material shoot outwards from the disk’s poles at nearly lightspeed. This is called an “engine” and is responsible for the production of GRBs.

In the case of Supernova 2012ap, scientists found that its jets initially projected at the speed of light but were quickly slowed down, imitating those seen in GRBs. This discovery showed the team that not all engine's produce gamma-ray bursts.

"This supernova had jets moving at nearly the speed of light, and those jets were quickly slowed down, just like the jets we see in gamma-ray bursts," said Alicia Soderberg, of the Harvard-Smithsonian Centre for Astrophysics.

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