The Guitar nebula: shocks at high velocity.

Like a speedboat screaming across a lake, a neutron star hurtling through a cloud of interstellar gas and dust generates a wake. Visible as a trailing skirt of glowing gas, this luminous region constitutes a shock-generated nebula.

Astronomers have now discovered a prominent, curiously shaped nebula caused by the motion of the fastest star yet observed in the Milky Way. Plowing through a gas cloud at more than 800 kilometers per second, this racing neutron star - designated PSR 2224+65 - carriers with it an intense magnetic field, which slams into the surrounding gas to create a shock wave that causes light emission.

James M. Cordes and Scott C. Lundgren of Cornell University and Roger W Romani of Stanford University describe their discovery in the March 11 NATURE.

The dense, compact remnant of an exploded star, PSR 2224+65 was originally detected as a pulsar - a spinning neutron star that sends out radio waves like a beacon. Created in a supernova about 1 million years ago, this object is roughly 20 kilometers wide and situated 6,000 light-years from Earth.

Though spinning relatively slowly, this neutron star is moving fast enough to eventually escape the galaxy In the years since its birth, the star has moved 50 degrees across the sky along a path nearly parallel to the galactic plane.

"It's a fairly average pulsar, but its forward motion is exceptional," Cordes says.

This striking feature prompted Cordes and his collaborators to observe the star and its environment at visible wavelengths. Using the 5-meter Hale telescope atop Mount Palomar in California, the researchers discovered the star at the leading edge of an elongated blob of brightly glowing gas. This bright head trails off into a faintly glowing "body" of varying width, suggesting a guitar shape.

"The length of the nebula that we see now corresponds to how far the pulsar has moved in 300 years," Cordes says. The sudden increase in brightness shows where the pulsar apparently entered a region with a significantly higher gas density

"Our observations provide some insights into the likelihood of finding shocks around other pulsars and the use of nebulae to find high-velocity neutron stars either not acting as pulsars or with their radiation beamed away from the Earth," the researchers note.