A speeding, superdense neutron star somehow got a powerful “kick” that is propelling it completely out of our Milky Way Galaxy into the cold vastness of intergalactic space. Its discovery is puzzling astronomers who used the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope to directly measure the fastest speed yet found in a neutron star.
The neutron star is the remnant of a massive star born in the constellation Cygnus that exploded about two and a half million years ago in a titanic explosion known as a supernova. Ultra- precise VLBA measurements of its distance and motion show that it is on course to inevitably leave our galaxy.
“We know that supernova explosions can give a kick to the resulting neutron star, but the tremendous speed of this object pushes the limits of our current understanding,” said Shami Chatterjee, of the National Radio Astronomy Observatory (NRAO) and the Harvard-Smithsonian Center for Astrophysics. “This discovery is very difficult for the latest models of supernova core collapse to explain,” he added.
Chatterjee and his colleagues used the VLBA to study the pulsar B1508+55, about 7,700 light-years from Earth. With the ultrasharp radio “vision” of the continent-wide VLBA, they were able to precisely measure both the distance and the speed of the pulsar, a spinning neutron star emitting powerful beams of radio waves. Plotting its motion backward pointed to a birthplace among groups of giant stars in the constellation Cygnus — stars so massive that they inevitably explode as supernovae.
“This is the first direct measurement of a neutron star’s speed that exceeds 1,000 kilometers per second,” said Walter Brisken, an NRAO astronomer. “Most earlier estimates of neutron-star speeds depended on educated guesses about their distances. With this one, we have a precise, direct measurement of the distance, so we can measure the speed directly,” Brisken said. The VLBA measurements show the pulsar moving at nearly 1,100 kilometers (more than 670 miles) per second — about 150 times faster than an orbiting Space Shuttle. At this speed, it could travel from London to New York in five seconds.