Tour of the Crab
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.
(Credit: NASA/CXC/MSFC/M.Weisskopf et al & A.Hobart)