Compact Binaries and the Origin of Millisecond Pulsars

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Neutron stars are formed when a massive star reaches the end of its life: the outer layers of the star are ejected in a violent explosion (a supernova) but the core of the star collapses to form a small, dense remnant. When neutron stars are formed, they are spinning rapidly – if the neutron star is isolated it will gradually spin down. However, neutron stars that are in a binary system with another star can be “spun up” if material from the companion star is deposited onto the neutron star surface. Neutron stars that have been “spun up” by a companion can rotate hundreds of times per second and are known as millisecond pulsars. Although many millisecond pulsars have been identified, the evolution of these systems, and how they fit within the family of other binaries, is not well understood. A team from Michigan State University (MSU) will undertake a survey of unidentified high energy sources that are likely to contain millisecond pulsars using the 4.3m Southern Astrophysical Research (SOAR) telescope. The goal of the survey is to find new millisecond pulsars, especially those with companions that may be in process of “spinning up” the pulsar. The Principal Investigator (PI) will expand a program at Michigan State University designed to give first year undergraduates from underrepresented groups the opportunity to participate in summer research. In addition, he will continue a pilot program to provide hands-on activities near the tailgating area for MSU football games. The goal of this program is to engage a wider range of people than is typically reached by traditional observatory nights.Observations with the NASA Fermi Gamma Ray telescope has shown that many millisecond pulsars are bright gamma-ray sources. More than a thousand Fermi gamma-ray sources remain unassociated with known sources, and many of these are undiscovered millisecond pulsars. The team will continue a program to target unidentified Fermi sources with the SOAR telescope. They will use low resolution optical spectroscopy to separate galactic from extragalactic sources and follow up candidate compact binaries with high cadence photometry to search for variability. Follow-up radio and X-ray observations will be used to confirm that a candidate source is indeed a millisecond pulsar. The SOAR observations have proven effective at not only classifying unassociated Fermi but also providing measurements of the orbital properties of gamma-ray emitting binaries: periods, inclinations, distances, and component masses. A major goal of the program is to find “transitional” sources: a low mass binary that transition to a rotation powered state.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.