Astrophysicists have taken a new and detailed look at the blazing heart of the Crab Nebula, the remnants of a star that exploded into view nearly 1000 years ago. Images from the orbiting Chandra X-ray Observatory reveal swirls of energetic material around the famed Crab pulsar, the spinning stellar corpse in the nebula's center. The swirls, especially a bright inner ring, may trace the long-sought "power conduits" that pump energy from the pulsar to the glowing nebula, according to researchers who spoke today at NASA Headquarters in Washington, D.C.
Chinese astronomers and Native Americans recorded the Crab as a new "star" in the year 1054. The celestial beacon was a supernova, the death blast of a giant star that had consumed all its fuel. Astronomers have known since 1968 that a pulsar--an ultradense neutron star left behind when the star's core collapsed--spins 30 times per second within the Crab's expanding cloud of debris, emitting a lighthouse beam of radio waves. However, the chaos at the center of the nebula has shrouded the mechanisms by which the pulsar lights up the glowing cloud.
The new x-ray observations lift that shroud, says Chandra project scientist Martin Weisskopf of NASA's Marshall Space Flight Center in Huntsville, Alabama. Chandra, launched 2 months ago, peered at the inner 40% of the Crab Nebula. A sharp ring of x-ray light encircles the pulsar at a distance of about one-third of a light-year. Chandra also exposed two jets shooting into space from the pulsar.
Astrophysicists believe these structures are the x-ray signatures of electrons and positrons accelerated by the pulsar's intense magnetic fields to nearly the speed of light. The magnetic fields whip the charged particles in tight spirals, forcing them to emit x-rays in the form of synchrotron radiation. These high-energy waves and jets then power the Crab's bright filaments of light. Chandra's images provide a roadmap that theorists will read to determine how that occurs, Weisskopf says. "These remarkable pictures may give us definitive clues about how the neutron star loses power and deposits it in the surrounding environment."
The brightest x-rays in Chandra's images coincide with the most dynamic parts of the nebula as seen in 1996 by the Hubble Space Telescope, says astronomer Jeff Hester of Arizona State University in Tempe. Hubble saw wisps, jets, and sprites that changed shape within days. "The ring is in exactly the right place to tie the pulsar with the larger nebula," Hester says.