The Physics of a Gamma-Ray Burst

Imagine sitting under the stars on a summer night and seeing a beam of light flash. Almost instantaneously, this flash travels towards earth, and the end result is the destruction of the ozone layer and everything following, including yourself. Gamma-Ray Bursts, or GRBs, have the power to do so. The immensity of a GRB is far greater than a supernova, and can be seen from the naked eye on earth from up to 7,000 lightyears away.

GRBs come in two different forms, shorter ones that occur from orbiting neutron stars that merge into each other and longer bursts that occur from hyper novae, massive stars exploding. In a short GRB, two stars are formed together as a binary star. They both go supernova, leaving two neutron stars orbiting each other. These two stars would orbit each other forever, however the subtle aspect of gravity predicted by Einstein's theory of relativity slowly pushes them together. The two stars lose orbital energy while circling around the axis, and after a long period of time they collapse on each other. A narrow jet, that has an angle from 2 to 20 degrees, beams out. Because the stars are orbiting so fast and compact, the explosion is a beam, and the flash of gamma-rays is short, only lasting about a millisecond. The result of this vast explosion is the birth of a black hole. 

Longer bursts can last up to 3 or 4 seconds. When the core of a very massive star collapses, forming a black hole, the outside of the core falls down forming an incredibly hot swirling maelstrom called an accretion disk. The magnetic field from that material and the black hole coil around, wrapped up by the rapidly spinning disk, it points up and down out of the disk and away from the black hole. This creates a giant beam of energy that lights up the universe, and can be carried through vast distances.

    

Theoretically, a GRB could hit earth and wipe out all of its creation. However, this is highly unlikely. GRB only happen close enough to hit earth once a millennium. The trajectory angle to hit earth would have to be very precise because of the small margin the beam hits. The further the distance traveled, the larger this margin becomes. By the time a big enough margin comes in contact with earth, the GRB will most likely become to weak to wipe out earth, and the ozone layer will protect us. 

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Weaver. "Gamma-Ray Burst Physics." Gamma-Ray Burst Physics. Penn State University, n.d. Web.