Session G3: Millisecond Pulsars

Testing Fundamental Physics with Radio Pulsars

Millisecond spin-period radio pulsars provide us with unique astronomical ``laboratories'' for exploring fundamental physics in a variety of ways -- from the physics of matter at super-nuclear density, to experimental tests of gravity, to the possible direct detection of gravitational radiation. In this talk, I will focus on our recent discovery of a two solar mass pulsar, currently the highest well-measured neutron star mass. In addition to several astrophysical implications, this measurement places constraints on theories of neutron star composition via the nuclear matter equation of state (EOS). Neutron stars are composed of the densest known stable form of matter, expected to be at least several times as dense as an atomic nucleus. The EOS of this material, and in particular the maximum stable mass before collapse to a black hole is inevitable, depends on the composition of the star's interior. Our new measurement either rules out or strongly constrains many proposed EOS that include ``exotic'' forms of matter such as hyperons, kaon condensates, or free quarks.   

Millisecond Pulsars at Gamma-Ray Energies: Fermi Detections and Implications

The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the discovery of new populations of radio quiet and millisecond gamma-ray pulsars. The Fermi Large Area Telescope has so far discovered $\sim 20$ new gamma-ray millisecond pulsars (MSPs) by both folding at periods of known radio MSPs or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with $\sim 30$ new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. Many of the newly discovered MSPs may be suitable for addition to the collection of very stable MSPs used for gravitational wave detection. Detection of such a large number of MSPs was surprising, given that most have relatively low spin-down luminosity and surface field strength. I will discuss their properties and the implications for pulsar particle acceleration and emission, as well as their potential contribution to gamma-ray backgrounds and Galactic cosmic rays.