Gamma-Ray Bursts

As cosmic events go, gamma-ray bursts (GRBs) and supernovae rank among the most spectacular, but nobody has sought to forge a link between the two ÐŽV until now. After three decades of study of their possible origins, researchers have concocted more than 150 theoretical models, but only a handful can come close to describing the true magnitude of the bursts. There are two leading theories ÐŽV the ÐŽ§collapsarЎЁ theory and the ÐŽ§supranovaЎЁ theory.

According to the popular collapsar theory, a GRB occurs when a very massive star explodes as a supernova and collapses into a black hole, i.e. a supernova will accompany the burst. In a competing supranova theory, a supernova comes first and a GRB follows few days later.

Gamma-ray Burst

GRBs were first discovered in 1967, quite by accident after U.S. satellites were deployed to monitor possible violations of the Nuclear Test Ban Treaty. At first, researchers thought they occurred relatively nearby, perhaps in our galaxy. But evidence collected in recent years shows that they are scattered throughout the universe ÐŽV all seemingly far away and hence, very old.

Gamma rays are the highest energy form of radiation. They are higher energy than X rays and are very penetrating. GRBs are the most powerful explosions in the universe. The explosions release most of their energy as gamma rays, hence the name. They occur randomly in time at any location in the sky and are extremely diverse. Much of the intensity of a GRB is concentrated between 100 KeV to 1 MeV, with some gamma rays as high as 50 GeV. The shortest yet seen lasted only 5 milliseconds, the longest a few hours, though most of them last between 1 and 100 seconds.

Despite their incredible size, gamma ray bursts flashed across the heavens without our knowing it until just a few decades ago. Gamma rays are particles of light ÐŽV or photons ÐŽV much like the ones we detect with our eyes. But gamma rays have much higher energy and cannot be seen. They also cannot pass through EarthÐŽ¦s atmosphere. Instead, they interact with the air and fizzle out in invisible showers of low-energy electrons, positrons (the antimatter twins of electrons), and other subatomic particles. So gamma ray bursts remained hidden until the Space Age began and scientists could send their instruments up above EarthÐŽ¦s life-giving blanket of gases.

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