Neutron stars are the unimaginably dense corpses of what were once much more massive stars that died while being ripped apart in a supernova explosion. Their average density is typically more than one billion tons per teaspoonful, even denser than the nucleus of an atom that is composed of protons and neutrons. Because these densities can never be reproduced on the Earth, these objects are great extraterrestrial laboratories for the study of how matter and exotic particles behave under extreme conditions.

Their existence was predicted in 1934 just one year after the discovery of the neutron, but it took another 30 years before the first neutron star was actually observed. Since that time, nearly all of the neutron stars that have had their masses accurately measured fall in a narrow range centered approximately on 1.4 times the mass of the Sun. Last October a group of astronomers using the Green Bank Radio Telescope found a neutron star that has a mass of nearly twice that of the Sun. The measurement of the mass is extremely precise because the neutron star is actually a pulsar (PSR J1614-2230) that spins on its axis at 317 times per second with clock-like regularity. What makes this discovery so remarkable is that the existence of a very massive neutron star allows astrophysicists to rule out a wide variety of theoretical models that claim that the neutron star could be composed of exotic subatomic particles such as hyperons or condensates of kaons.

One of the big questions that arises is “how does Nature produce these very massive neutron stars?” Are they born that way or did they grow because they gravitationally strip mass from a nearby star? One of the clues to the origin of this pulsar is that it is not alone. It is found in a very close 9-day binary orbit with another dead star known as a white dwarf. According to Professor Lorne Nelson (Bishop’s University) and his colleagues at MIT, Oxford, and UCSB, the neutron star was likely spun up to become a fast-rotating (millisecond) pulsar as a result of the neutron star having cannibalized its stellar companion many millions of years ago, leaving behind a dead core composed mostly of carbon and oxygen. According to Nelson, “Although it is common to find a high fraction of stars in binary systems, it is rare for them to be close enough so that one star can strip off mass from its companion star. But when this happens, it is spectacular.”

In order to understand how this binary formed, their strategy was to compute a grid of theoretical models that would describe how binary systems evolve over the entire lifetime of the Universe. Thanks to the incredible number-crunching power of supercomputers, Nelson and his collaborators were able to calculate the evolution of more than 40,000 plausible starting cases for the binary and determine which ones were relevant. As they describe at this week’s CASCA meeting in Ontario, Canada, they found several cases where the neutron star could grow significantly in mass at the expense of its companion, but as Nelson says, “It isn’t easy for Nature to make such high-mass neutron stars, and this probably explains why they are so rare.”

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The team would like to acknowledge the computing time granted and support provided by the Reseau quebecois de calcul de haute performance (RQCHP) and Compute Canada.

The University of Western Ontario is proudly hosting the 2011 CASCA conference May 30 to June 2, 2011, in London, Ontario, to celebrate Canadian astronomical and astrophysical research: http://www.casca2011.com/index.html

The Canadian Astronomical Society (http://www.casca.ca) was founded in 1971 and incorporated in 1983 as a society of professional astronomers. The society is devoted to the promotion and advancement of knowledge of the universe through research and education. Membership is open to persons with a professional involvement with these goals in astronomy and the related sciences. The main activities of the Society are its annual scientific meetings, the planning and realization of scientific projects, the support of the scientific activities of its members, and the dissemination of related information among members and other interested persons. The Society supports committees on Optical and Infrared Astronomy, Radio Astronomy, Space Astronomy, Theoretical Astronomy, Education, Heritage, Canadian Grad Students, and Awards. Cassiopeia, the quarterly newsletter of the Society, is published at equinoxes and solstices.

Press Contacts:
Leslie Sage
CASCA Press Officer
+1 (301) 675-8957 (cell)
cascapressofficer@gmail.com

Dave McBride
Public Relations Manager
Bishop’s University
(819) 822-9600 x2762
dmcbride@ubishops.ca

Science Contact:
Lorne Nelson
Department of Physics
Bishop’s University
(819) 822-9600 x2372
lnelson@ubishops.ca