||[Dec. 20th, 2007|12:45 am]
Is There Something You Want to Say to the World?
Hey there; queenlyzard asked me to post about this.|
The [compound] word is: relativistic fireball shock
The relativistic fireball shock model is a successful scientific theory that explains much of the phenomena related to gamma-ray bursts. A gamma-ray burst is essentially the most energetic and brightest event in the universe, save for the Big Bang itself. Yes, that includes supernovas. GRBs are way brighter than supernovas; they release more energy than the sun would if it lived for 880 billion years, all within the span of milliseconds to minutes. Literally. How much energy is that? If one were to go off within ~3,500 light-years of Earth (that's about 2.06 × 1016 miles), and if it were pointed at us (they emit energy along a specific axis only, kinda light a spotlight), we'd be toast.
Anyway, here's a cut-and-paste from this Scientific American article, which explains it pretty well:
...the initial energy release of the explosion is stored in the kinetic energy of a shell of particles-- a fireball-- moving at close to the speed of light. The particles include photons as well as electrons and their antimatter counterpart, positrons. This fireball expands to a diameter of 10 billion to 100 billion kilometers, by which point the photon density has dropped enough for the gamma rays to escape unhindered. The fireball then converts some of its kinetic energy into electromagnetic radiation, yielding a GRB.In a nutshell: explosions that are sufficiently powerful to create gamma-ray bursts first give off fireballs at close to the speed of light (this is where the "relativistic" part of the name comes from). Shockwaves are generated in the fireball from things moving at different speeds, and this accounts for first the gamma-ray emission itself, then the less energetic afterglow.
The initial gamma-ray emission is most likely the result of internal shock waves within the expanding fireball. Those shocks are set up when faster blobs in the expanding material overtake slower blobs. Because the fireball is expanding so close to the speed of light, the timescale witnessed by an external observer is vastly compressed, according to the principles of relativity. So the observer sees a burst of gamma rays that lasts only a few seconds, even if it took a day to produce. The fireball continues to expand, and eventually it encounters and sweeps up surrounding gas. Another shock wave forms, this time at the boundary between the fireball and the external medium, and persists as the fireball slows down. This external shock nicely accounts for the GRB afterglow emission and the gradual degradation of this emission from gamma rays to x-rays to visible light and, finally, to radio waves.