The Hyperfast Pulsar B1508+55

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. [...] The VLBA measurements show the pulsar moving at nearly 1100 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.

Click on the image above for a larger version of the illustration (by Bill Saxton, NRAO/AUI/NSF) showing the path of the pulsar since its birth.

The Science

• The final published version (PDF, 81KB) of the paper: 2005 ApJ 630, L61 (1 Sep 2005 issue).
  Also available on astro-ph.

  Abstract: The highest velocity neutron stars establish stringent constraints on natal kicks, asymmetries in supernova core collapse, and the evolution of close binary systems. Here we present the first results of a long-term pulsar astrometry program using the VLBA. We measure a proper motion and parallax for the pulsar B1508+55, leading to model-independent estimates of its distance (2.37+0.23-0.20 kpc) and transverse velocity (1083+103-90 km/s), the highest velocity directly measured for a neutron star. We trace the pulsar back from its present Galactic latitude of 52.3 degrees to a birth site in the Galactic plane near the Cyg OB associations, and find that it will inevitably escape the Galaxy. Binary disruption alone is insufficient to impart the required birth velocity, and a natal kick is indicated. A composite scenario including a large kick along with binary disruption can plausibly account for the high velocity.

• A poster (353K, PDF) presented at "A Life with Stars", Amsterdam, 22-26 August 2005. Note that this is formatted for letter paper, and needs to be magnified 4x for the normal poster size.

B1508+55 in the news

• The press release text, also archived at NRAO, at the CfA and at Jodrell Bank (UK version).
• Scientific American ran a blurb.
• The New Scientist did a short article.
• So did Space.com (also appearing on Yahoo! News).
• And it appeared on the Royal Astronomical Society's news page, and in the Spotlight on Science at the Smithsonian.
• Astronomy Magazine wrote up some intriguing speculation that B1508+55 may be a quark star, but they cited their source --- Arzoumanian, Cordes, & Chernoff (2002), as interpreted by Bombaci & Popov (2004) --- so all is forgiven.
• Sky and Telescope reviewed it (to appear in the December 2005? issue), as did Astronomy Now magazine in the U.K.
• The Bad Astronomy blog wrote a very nice piece about it.
• Several places ran the press release: PhysOrg.com, Universe Today, Spaceflight Now, Red Nova.
• And not to forget the Socorro El Defensor Chieftain.
• Some foreign language press too: Stern, ScienceTicker, Hispamp3, Espacial.com.
• The Calcutta Telegraph picked up the story.
• It even made the front page of Slashdot! Wow!

Shami Chatterjee Contact Information Last Modified: 15 Nov 2005