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Session 45 - The Structure and Evolution of The Universe - II.
Topical, Oral session, Tuesday, June 09
Presidio,
Neutron stars provide a rich and unique cosmic laboratory for studying fundamental questions in physics and astrophysics, including the effects of superstrong magnetic fields, nuclear deflagration and detonation in dense matter, neutron superfluidity and proton superconductivity, the properties of the nuclear force at high densities, the expected transition to quark matter, and gravitational physics in the strong-field regime. X- and \gamma-radiation that comes from neutron stars is an especially valuable probe of these stars and their environments. Measurements of X-ray emission from the bursting pulsar using the Rossi X-Ray Timing Explorer have overturned cherished beliefs about accretion-powered pulsars and X-ray bursts. Studies with the Rossi Explorer are expected to test the conjecture that the soft \gamma-ray repeaters are neutron stars with magnetic fields \sim10^15 G. The dramatic discovery with the Rossi Explorer that many accreting neutron stars generate very strong, remarkably coherent, high frequency QPOs is making possible quantitative studies of gas dynamics in strongly curved spacetime, nuclear burning in dense matter, and the properties of neutron stars. In particular, precise measurements of the kilohertz QPOs observed in the persistent emission and the high-frequency oscillations observed during X-ray bursts are providing the first ever determinations of the spin frequencies of these stars, restrictions on their masses, radii, and compactness, and important new constraints on the equation of state of dense matter. Compelling evidence of an innermost stable circular orbit around a neutron star would be the first confirmation of a strong-field prediction of general relativity. Given the continuing rapid pace of discoveries using the Rossi Explorer, the prospects for obtaining such evidence appear good. Upcoming and planned NASA missions such as AXAF, GLAST, and Constellation-X will advance these studies in important ways and are likely to produce important new discoveries.
