The Crab Nebula is one of the brightest sources
of high-energy radiation in the sky. Little
wonder - it's the expanding remains of an
exploded star, a supernova seen in 1054. Scientists
have used virtually every telescope at their
disposal, including NASA's Chandra X-ray Observatory,
to study the Crab. The supernova left behind
a magnetized neutron star - a pulsar. It's
about the size of Washington DC, but it spins
30 times a second. Each rotation sweeps a
lighthouse-like beam past us, creating a pulse
of electromagnetic energy detectable across
the spectrum.
Here's what the sky looks like in high-energy
gamma rays. The pulsar in the Crab Nebula
is among the brightest sources. Recently,
NASA's Fermi Gamma Ray Observatory and Italy's
AGILE Satellite detected strong gamma-ray
flares from the Crab, including a series of
"superflares" in April 2011. To help pinpoint
the location of these flares, astronomers
enlisted Chandra.
With its keen X-ray eyes, Chandra saw lots
of activity, but none of it seems correlated
with the superflare. This hints that whatever
is causing the flares is happening with about
a third of a light year from the pulsar. And
rapid changes in the rise and fall of gamma
rays imply that the emission region is very
small, comparable in size to our Solar System.
The Chandra observations will likely help
scientists to home in on an explanation of
the gamma-ray flares one day. The Chandra
data provide strong constraints on the behavior,
at relatively low energies, of the particles
that have been accelerated to produce the
gamma-ray flares. Even after a thousand years,
the heart of this shattered star still offers
scientists glimpses of staggering energies
and cutting edge science.
