Gamma-Ray Bursts: Introduction to a Mystery
A computer animation of a gamma-ray burst destroying a star. (10 MB QT)|
(Credit: NASA / SkyWorks Digital)
Gamma-ray bursts are short-lived bursts of gamma-ray photons, the most energetic form of light. At least some of them are associated with a special type of supernovae, the explosions marking the deaths of especially massive stars.
Lasting anywhere from a few milliseconds to several minutes, gamma-ray
bursts (GRBs) shine hundreds of times brighter than a typical
supernova and about a million trillion times as bright as the Sun,
making them briefly the brightest source of cosmic gamma-ray photons
in the observable Universe. GRBs are detected roughly once per day
from wholly random directions of the sky.
Until recently, GRBs were arguably the biggest mystery in high-energy
astronomy. They were discovered serendipitously in the late 1960s by
U.S. military satellites which were on the look
out for Soviet nuclear testing in violation of the
nuclear test ban treaty. These satellites carried gamma ray detectors since
a nuclear explosion produces gamma rays. As recently as the early 1990s,
astronomers didn't even know if GRBs originated at the edge of our solar
system, in our Milky Way Galaxy or incredibly far
away near the edge of the observable Universe. (That is, they
didn't know how far away GRBs were to within a factor of a few billion
light years!) But now a slew of satellite observations, follow-up
ground-based observations, and theoretical work have allowed
astronomers to link GRBs to supernovae in distant galaxies.
In this series of articles we will explore what astronomers know
about gamma-ray bursts, what they think causes them, the evidence for the
theories, and the lingering mysteries. Along the way we'll encounter
powerful hypernovas and strange Wolf-Rayet stars.