Crab's shocking secret

Shockwaves plough outwards from the pulsar

By Dr David Whitehouse BBC News Online science editor

Matter and antimatter are being propelled through space at nearly the speed of light by the Crab pulsar - a rapidly rotating neutron star just a few kilometres across.

By combining the power of the Chandra and Hubble space-borne observatories, astronomers have detected features never seen before.

"The Crab Nebula has come to life," says Jeff Hester of Arizona State University, US. "We can see how this awesome cosmic generator actually works."

By understanding the Crab, astronomers hope to unlock the secrets of how similar objects across the Universe are powered.

Expanding ring

The Crab Nebula is the expanding debris of an exploded star that was seen by the Chinese in 1054. At the heart of the stellar wreckage is a small, superdense object called a pulsar.

Expanding shockwaves circle the pulsar

The pulsar is a rapidly spinning star only a few kilometres in size. The star sweeps intense magnetic fields around it that accelerate and eject electrically charged matter.

The inner region of the Crab Nebula around the pulsar was observed with Hubble on 24 occasions between August 2000 and April 2001, and with Chandra on eight occasions between November 2000 and April 2001.

Bright wisps can be seen in both visible and X-ray images that are moving outward at half the speed of light forming an expanding ring.

Turbulent jet

The wisps appear to come from a shockwave that can be seen as an inner X-ray ring. It consists of about 20 knots that form, brighten and fade, occasionally undergoing outbursts that give rise to expanding clouds of sub-atomic particles.

"These data leave little doubt that the inner X-ray ring is the location of the shockwave that turns the high-speed wind from the pulsar into extremely energetic particles," said Koji Mori of Pennsylvania State University, US.

Another dramatic feature is a turbulent jet that lies perpendicular to the inner and outer rings.

"The jet looks like steam from a high-pressure boiler," said David Burrows, also of Pennsylvania State University, "except when you realise you are looking at a stream of matter and anti-matter electrons moving at half the speed of light!"

Energetic processes around the Crab Nebula could help astronomers understand similar objects elsewhere in the Universe, such as rotating black holes at galactic cores.