Summer 2004 -- Vol. 21

Space Movie Shows Shocking Secrets of the Crab Pulsar

	A composite image of the Crab Nebula showing the X-ray (blue), and optical (red) images superimposed. The size of the X-ray image is smaller because the higher energy X-ray emitting electrons radiate away their energy more quickly than the lower energy optically emitting electrons as they move. The inner ring is about one light year across. Photo Credit: X-ray: NASA/CXC/ASU/ J. Hester et al.; Optical: NASA/HST/ASU/J. Hester et al.

Just when it seemed like the summer movie season had ended, two of NASA’s Great Observatories produced their own action movie. Multiple observations made over several months with NASA’s Chandra X-ray Observatory and the Hubble Space Telescope captured the spectacle of matter and antimatter propelled to near the speed of light by the Crab pulsar, a rapidly rotating neutron star the size of Manhattan.

David N. Burrows, professor of astronomy and astrophysics at Penn State, is among the scientists who revealed the movie at NASA headquarters in Washington, DC.

The Crab was first observed by Chinese astronomers in 1054 A.D. and has since become one of the most studied objects in the sky. By combining the power of both Chandra and Hubble, the movie reveals features never seen in still images. By understanding the Crab, astronomers hope to unlock the secrets of how similar objects across the universe are powered.

“Through this movie, the Crab Nebula has come to life,” said Jeff Hester of Arizona State University in Tempe, lead author of a paper in the Astrophysical Journal Letters on which Burrows and Koji Mori, a research associate at Penn State, are co-authors. “We can see how this awesome cosmic generator actually works.”

Bright wisps can be seen moving outward at half the speed of light to form an expanding ring that is visible in both X-ray and optical images. These wisps appear to originate from a shock wave that shows up as an inner X-ray ring. This ring consists of about two dozen knots that form, brighten and fade, jitter around, and occasionally undergo outbursts that give rise to expanding clouds of particles, but remain in roughly the same location.

X-ray, Optical & Radio Composite A composite image of the Crab Nebula showing X-ray in blue, optical in green, and radio in red. Photo Credit: X-ray: NASA/CXC/ASU/J. Hester et al.; Optical: NASA/HST/ASU/J. Hester et al.; Radio: VLA/NRAO

“These data leave little doubt that the inner X-ray ring is the location of the shock wave that turns the high-speed wind from the pulsar into extremely energetic particles,” Mori said.

Another dramatic feature of the movie is a turbulent jet that lies perpendicular to the inner and outer rings. Violent internal motions are obvious, as is a slow motion outward into the surrounding nebula of particles and a magnetic field.

“The jet looks like steam from a high-pressure boiler,” said Burrows, “except when you realize you are looking at a stream of matter and anti-matter electrons moving at half the speed of light!”

The inner region of the Crab Nebula around the pulsar was observed with Hubble between August 2000 and April 2001, and with Chandra between November 2000 and April 2001. The Crab was observed with Chandra’s Advanced CCD Imaging Spectrometer and Hubble’s Wide-Field Planetary Camera.

Megan Watzke and Barbara K. Kennedy

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