Probing Extreme Physics Through Analysis of Neutron Star Surface Emission

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Neutron stars present some of the most extreme physical conditions in the universe - conditions which cannot be studied through laboratory experiments here on Earth. Here Dr. Bhattacharyya and collaborators will focus on three specific problems which can only be addressed by studying neutron stars: (1) understanding the super-dense cold matter in neutron star cores, which may contain exotic matter (e.g., meson condensates, deconfined quarks, etc.). This has been an unsolved problem of fundamental physics for more than 35 years, and can be resolved only by accurate measurements of the mass, radius and spin period of a neutron star. (2) Performing strong-field tests of the predictions of general relativity. (3) Understanding how thermonuclear flames spread on neutron star surfaces during type I X-ray bursts, which will also provide unique opportunities to probe the behavior of magnetized atmospheres under extreme conditions. These studies will have significant impact on various fields, including nuclear physics, magnetohydrodynamics, and general relativity. In the first two years, the team will carry out: an exhaustive analysis of type I burst data from the Rossi X-ray Timing Explorer (RXTE) satellite, and the simultaneous fitting of the observed fast timing features and broad-band spectra with the rigorous models already developed by the team (this will constrain properties of neutron stars); a careful analysis of data from Chandra and X-ray Multi-Mirror-Newton satellites to determine the chemical composition of the fuel and other aspects of the type I bursts, and to search for spectral lines from neutron star surfaces (both will be useful for constraining stellar parameters); detailed theoretical study of the shapes of surface spectral lines for prescribing a realistic way to detect the frame-dragging predicted by general relativity, and estimation of the capabilities of future X-ray satellites for this detection; and finding significant time evolution of various burst properties for each type I burst in the RXTE data archive (this will aid in the understanding of flame spreading). In the third year, the team will focus on: the modeling of persistent pulsation light curves from accreting millisecond pulsars (this will involve general relativistic ray tracing in a scattering corona, and will constrain neutron star parameters); and simulation of flame spreading including the effects of magnetic fields, in order to model the RXTE data. These projects may yield a breakthrough in the behavior of matter in extreme conditions.It is expected that this research will have an impact on several fields of physics. It has strong potential to establish collaborations among different disciplines and institutions. The team will disseminate the scientific results through publications in journals and presentations at scientific meetings. The team will also discuss their findings in popular journals, and give public talks at the University of Maryland Observatory and in other forums.