RUI: Neutron Star Crusts in Multi-Messenger Astronomy: Probability Distributions of Ground State and Accreted Crusts with Rigorously Quantified Modeling Uncertainty.

East Texas A&M University, Commerce TX

Investigators

Abstract

The densest matter in the universe is contained within neutron stars – an object with the mass of our Sun and the size of a city left behind after a supernova explosion. The properties of this matter remain a mystery and could shed light on the fundamental interactions of nature. A number of cutting edge astronomical observatories coupled with the latest in laboratory experiments on dense matter are gathering data on this most exotic of materials. Our best models predict that the outer layer of the star, about half a mile thick, is a solid (the crust), and the bulk of the star beneath is a liquid. Over the last decade, a huge effort been expended measuring the properties of the star overall. However, a similar effort has not yet been devoted to understanding the properties of the crust of the star, despite its impact on the way neutron stars change their temperature, rotation and magnetic field over time, and give rise to exciting phenomena such as starquakes. The PI will address this imbalance by subjecting the crust to similar state-of-the-art techniques as have been developed for studying the core. The PI will examine the material properties of both the crusts the neutron stars are born with, and those neutron stars end up with after matter from a companion star falls onto their surface. The PI will mentor students from underrepresented groups and give them experience conducting research and developing a wide range of associated skills. The last decade has seen the nuclear astrophysics community focus on extracting the neutron star equation-of-state (EOS) from measurements of the masses and radii of neutron stars by performing statistical analyses on large ensembles of systematically generated EOSs. In part this is a response to a marked increase in the quality of the data with the advent of a number of cutting-edge observatories and experiments including the Laser Interferometric Gravitational-wave Observatory (LIGO), NASA’s Neutron star Interior Composition ExploreR (NICER) on the astronomy side, and the Lead (Pb) Radius Experiment (PREX) and the newly completed Facility for Rare Isotope Beams (FRIB) on the nuclear experimental side. Finding the overall EOS is just one strand of research into the interior properties of the star. Many observed phenomena are a direct result of the neutron star having a solid crust about a kilometer thick. The cooling of neutron stars, rotational anomalies such as pulsar glitches, persistent gravitational waves, magnetic field evolution and starquakes could all bear the signatures of the physics of the neutron star crust. This project will subject the crust to the same statistical scrutiny as the EOS of the star, developing large ensembles of crust models and applying astrophysical and nuclear data to obtain, for the first time, constraints with well characterized uncertainty on the material properties of crusts, and determine how those properties change when a neutron star accretes material from a companion. This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.