Astrophysics of Neutron Stars and Supernova Remnants

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The proposed work is basic research with the goals of (A) learning about the fundamental nature of matter, using neutron stars, and of (B) understanding the life-cycle of matter, using supernova remnants. A neutron star is an extremely dense object created when a massive star explodes. Its density is higher than an atomic nucleus (100 trillion times the density of water), higher than anywhere else in the universe. Its mass is similar to that of our sun (1 million times as massive as the Earth). A supernova remnant is the hot (million degree) gas heated by the explosion of a star (a supernova). The gas shoots out into the space between the stars at about a million miles per hour. For neutron stars, this work will measure mass and radius values. The mass and radius depend on the density and pressure of nuclear matter, thus these measurements are crucial and will be used to understand the physics of nuclear matter (Lattimer and Prakash, 2016, Physics Reports, 621, 127). My work takes two approaches. 1) Observations of X-ray binary systems will be modeled. My multi-decade study of Hercules X-1 has yielded system geometry and properties, and mass-to-radius ratio for the neutron star. The next step is to measure system inclination, which will yield mass and radius for the neutron star. 2) X-ray pulse shapes of millisecond pulsars will be modeled to obtain mass and radius values: this will be done in collaboration with international experts.For supernova remnants (SNRs), this work will determine supernova (SN) explosion energies, ages, birthrates and the nature of the surrounding gas before the explosion. This is accomplished by i) determining distances to SNRs, and ii) modelling multi-wavelength observations of SNRs. Determining distances is a technical problem for which I am a world expert in collaboration with Dr. Tian of Beijing Astronomical Observatory. Modelling SNR is my other focus. The hot gas, which is the main part of a SNR, emits X-rays. I use models of X-ray emission to tell us the properties of SNR. SNRs are long-lived compared to SN (about 50,000 yr compared to 1 month), so SN explosions can be well studied using SNRs. With a sufficient number of SNRs, general properties of SN explosions will be determined. The explosion shock determines how most elements in our Galaxy, and on Earth, are created. The explosion energy determines the motions of the gas in our Galaxy, and how this gas can form new stars. Studying SNRs is the best way to learn about SN and their effects on the nature of our Galaxy, including how new stars form, and the properties and elemental composition of the gas between the stars.The benefits to Canada include enhancement of Canada's reputation in fundamental science, and training graduate students to be the next-generation problem solvers. For astrophysics, the understanding neutron stars and supernova remnants improves our understanding of massive stars, which have effects on all scales in our universe.