Professor James Lattimer
Department of Physics and Astronomy
7:30 pm Room 001 ESS Building
Friday, February 1, 2013

The Discovery of Superfluidity in the Core of a Neutron Star

X-ray emission from the neutron star remnant of the 1680 supernova explosion in the constellation of Cassiopeia was the "first light" observed with the Chandra X-ray Telescope in 1999. This neutron star is now at the center of an expanding plasma known as Cas A. The analysis of 2000-2010 data from Cas A revealed that the neutron star is cooling more than 15 times faster than originally expected. A team composed of researchers, all of whom had close ties to Stony Brook, showed that this rapid cooling could be explained by to the onset, less than 30 years earlier, of neutron superfluidity in the star's core. (A competing team of Russians also suggested this explanation.) A superfluid is a novel state of matter, with bizarre properties, in which particles weakly pair with each other. In terrestrial matter, superfluids usually form only within tens of degrees of absolute zero, but in a neutron star interior, they are expected to form below about a half billion degrees Kelvin. In the case of neutrons, which are fermions, the pairs, called Cooper pairs, are bosons. As the internal temperature falls below the superfluid critical temperature, Cooper pairs form and then break due to thermal fluctuations. The continued formation and breaking of Cooper pairs drives neutrino emissions that cool the star. It is expected that the observed enhanced cooling will continue for about 100 more years, but within about 30 years we should observe a noticeable change in the cooling rate. This is the first time that the surface temperature of a neutron star that is not a source of X-ray bursts has been observed to change in real time, and the first solid evidence of superfluidity in a neutron star's deep interior.

James Lattimer, a professor of Physics and Astronomy at Stony Brook University, has a long-standing interest in neutron stars, including their structure, composition, formation and evolution. He is a Fellow of the American Physical Society. Also a ferroequinologist, he enjoys observing with his $10 Dobsonian telescope on Camano Island.