A team using the Very Long Baseline Array's 10 radio telescopes - which span 5,000 miles from Hawaii to the U.S. Virgin Islands - studied fast-spinning neutron star B1508+55, which is located about 7,700 light-years away. The VLBA's ultra-sharp vision in the radio part of the spectrum allowed the astronomers to pinpoint both the distance and the speed of the pulsar - which they calculated to be more than 2.4 million miles per hour.

They then retraced the star's motion back to its birthplace among groups of giant stars in the constellation Cygnus, stars so massive they inevitably explode as supernovae.

Astronomer James Cordes of Cornell University, his former student Shami Chatterjee, now of the Harvard-Smithsonian Center for Astrophysics, and colleagues said they measured the pulsar's distance by detecting the very slight wobble in its position caused by the Earth's motion around the sun. This enabled them to calculate the pulsar's speed by measuring its motion across the sky.

"The motion we measured with the VLBA was about equal to watching a home run ball in Boston's Fenway Park from a seat on the Moon," Chatterjee said. "The pulsar took nearly 22 months to show that much apparent motion (and the) VLBA is the best possible telescope for tracking such tiny apparent motions."

Cordes said the team thinks the pulsar's speed is the result of the implosion of the core of a star that took only a few seconds about 2.5 million years ago. The resulting explosive recoil kicked the remnant so hard it is now leaving the galaxy, like a football sailing far past the goalposts, over the grandstands and out of the stadium.

The VLBA measurements showed the pulsar moving at a speed by which it could travel from London to New York, or more than 3,300 miles, in five seconds - a speed so fast it eventually will escape the Milky Way's gravitational attraction. Since the supernova, the pulsar has moved across about one-third of the night sky as seen from Earth.

"We've thought for some time that supernova explosions can give a kick to the resulting neutron star, but the latest computer models of this process have not produced speeds anywhere near what we see in this object," Chatterjee said. "This means that the models need to be checked, and possibly corrected, to account for our observations," he said, noting that other processes could be at work as well.

"The reason this (observation) is so different is the precision of it," Cordes said. "In astronomy one of the big problems is getting the distance scale. In the past we've identified objects whose velocity we've estimated, but what makes this special is there's no uncertainty in the distance. It's ironclad. There's no wiggle room. It gets rid of any question."

The observations were part of a larger project to use the VLBA to measure the distances and motions of pulsars. "This is the first result of this long-term project, and it's pretty exciting to have something so spectacular come this early," said team member Walter Brisken of the National Radio Astronomy Observatory, which operates the array.

Each of the radio telescopes in the VLBA, which is funded by the National Science Foundation, has a dish 25 meters (82 feet) in diameter and weighs 240 tons. The VLBA provides astronomers with the sharpest vision of any telescope on Earth or in space.

Related Links
National Radio Astronomy Observatory
Very Long Baseline Array

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