Variable stars highlight an important fact about the heavens above us: the universe is always changing. The universe is very large, stars and galaxies are very far away, and many changes occur on timescales far longer than we can see. Most things in the sky -- stars, nebulae, and galaxies -- don't appear to change at all during the course of a human lifetime.
A gamma-ray burst (GRB) is a brief flash of gamma rays coming from an astrophysical source at great distances from us, often from hundreds of millions of light years away. Gamma rays are a kind of light (like visible light, microwaves, or X-rays) that is very energetic, and whatever produces gamma rays must therefore contain (and unleash) a large amount of energy in a very short amount of time. Thus the study of gamma ray bursts is a study of some of the most violent events in the universe.
