A newly discovered pulsar, just 700 years old, is giving astronomers a new perspective on the early life of these whirling beacons. The pulsar spins slower than its peers, suggesting a surprisingly strong magnetic field--and a short life.
Pulsars live millions of years, but they are created in a few seconds of tremendous devastation. At the end of a star's life, its outer layers collapse. A ferocious explosion then bounces almost all of the debris into space. The leading edge of the explosion crashes into interstellar gas, creating a fiery ring called a supernova remnant. Left behind at ground zero is a whirling magnetized nugget of neutrons smaller than Manhattan but weighing as much as the sun. That neutron core--the pulsar--spews a rotating beam of radiating particles that creates the telltale flashing searchlight first detected by radio astronomers 3 decades ago. Since then, many examples of mature pulsars have turned up, but none younger than 1000 years. This means pulsar childhood--during which the pulsar radiates away most of its rotational energy--has remained mysterious.
Eric Gotthelf of Columbia University has now caught a glimpse. While hunting a suspected pulsar with the Rossi X-ray Timing Explorer (RXTE), he noticed x-ray pulses arriving every 0.3 seconds from the same large patch of sky. A search through x-ray image archives quickly showed Gotthelf that he had a unique prize. In some of the images, the pulsar was winking at him from the center of a 700-year-old supernova remnant Kes 75. Although Kes 75 had been searched for a pulsar, "the signal was not strong enough to see [it] with anything but RXTE," Gotthelf explains. By timing the pulses, Gotthelf's team discovered that the pulsar was slowing down rapidly, implying that it has a magnetic field 10 times as strong as the prototypical young pulsar in the 1000-year-old Crab Nebula.
Because the lifetime of a pulsar is inversely proportional to its magnetic field strength, pulsars like Kes 75 must live very short lives, notes astrophysicist Shri Kulkarni of the California Institute of Technology. But the complete story won't be pieced together until many other young pulsars are found. Fortunately, Kulkarni expects orbiting x-ray telescopes like RXTE, NASA's Chandra, and the X-ray Multi-Mirror telescope to find several more examples of young pulsars in the coming years.
Listen to pulsar radio signals, which sound like a bouncing basketball or a badly tuned Harley.