Considering that people often have trouble finding their keys in their own homes, it's hardly surprising that astronomers sometimes have difficulty locating objects situated thousands of light-years away from Earth. A pulsar dubbed PSR B0656+14 has proved to be one such elusive object. Now a report published in the August 20 issue of the journal Astrophysical Journal Letters provides the most accurate distance measurement yet for the pulsar and in so doing may help resolve a mystery about cosmic rays.

Previous research had suggested that PSR B0656+14 resided 2,500 light-years away, but the distance was measured only indirectly. Walter Brisken of the National Radio Astronomy Observatory and his colleagues used the Very Long Baseline Array of telescopes, which stretches from Hawaii to the U.S. Virgin Islands, to take a more detailed look at PSR B0656+14 between 2000 and 2002. Making a direct measurement, they found that the pulsar is closer than previously thought and sits next to the so-called Monogem Ring, a circular supernova remnant. "Our measurements showed that the pulsar is about 950 light-years from Earth, essentially the same distance as the supernova remnant," says team member Steve Thorsett of the University of California at Santa Cruz. "That means that the two almost certainly were created by the same supernova blast."

The improved coordinates could explain a recently detected surplus of cosmic rays--subatomic particles and atomic nuclei accelerated to close to the speed of light--whose origin was unknown. Brisken notes that "our measurement now puts PSR B0656+14 and the Monogem Ring at exactly the right place and at exactly the right age to be the source of this excess of cosmic rays."