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Wednesday, September 29, 1999 Published at 11:28 GMT 12:28 UK


Crab's ring of power

Chandra sees the most energetic particles produced by the pulsar

By BBC News Online Science Editor Dr David Whitehouse

Nasa's Chandra X-ray Observatory has taken a stunning image of the Crab Nebula, the remnant of a stellar explosion seen in 1054.

Sensitive to X-rays from superhot gas, Chandra has revealed something never seen before: a brilliant ring around the nebula's heart.

[ image: As particles lose their energy, visible light can be detected in the Crab (Paloma Observatory)]
As particles lose their energy, visible light can be detected in the Crab (Paloma Observatory)
Astronomers know that the stellar wreckage is expanding into space and that at the very heart of the nebula is a tiny, rapidly-spinning, superdense object called a pulsar.

It is the slowing down of this pulsar, which is spinning many times a second, that is powering the nebula, keeping it hot and radiating the X-rays that Chandra sees.

"The inner ring is unique," said Professor Jeff Hester of Arizona State University. "It has never been seen before, and it should tell us a lot about how the energy from the pulsar gets into the nebula. It's like finding the transmission lines between the power plant and the light bulb."

Professor Mal Ruderman of Columbia University, New York, agrees. "The X-rays Chandra sees are the best tracer of where the energy is. With images such as these, we can directly diagnose what is going on."

Knots and wisps

What is going on, according to Dr. Martin Weisskopf, Chandra Project Scientist from Nasa's Marshall Space Flight Center, is awesome. "The Crab pulsar is accelerating particles up to the speed of light and flinging them out into interstellar space at an incredible rate."

The image shows tilted rings or waves of high-energy particles that appear to have been flung outward over the distance of a light year (10 million, million km) from the central pulsar as well as high-energy jets of particles blasting away at right angles to the rings.

[ image: The Keck Observatory took this infrared image, which captures particles with even lower energies than visible light]
The Keck Observatory took this infrared image, which captures particles with even lower energies than visible light
Detailed Hubble Space Telescope images have shown moving knots and wisps around the pulsar, and previous X-ray images have shown the outer parts of the jet and hinted at the ring structure.

But with Chandra's exceptional resolution, the jet can be traced all the way in to the neutron star, and the ring pattern clearly appears.

The Crab Nebula, is one of the most studied objects beyond our Solar System. It is the remnant of a star that was observed to explode in AD 1054 by Chinese astronomers.

It is located 6,000 light years from Earth in the constellation Taurus. The Crab pulsar, which was discovered by radio astronomers in 1968, is a neutron star rotating 30 times per second. Neutron stars are formed in the seconds before a supernova explosion when gravity crushes the central core of the star to densities 50 trillion times that of lead with a diameter of only 12 miles.

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