Ultracompact binaries: Gravitational wave sources and supernova Ia progenitors

Texas Tech University, Lubbock TX

Investigators

Abstract

Studies of Ultra-compact binaries (UCBs), consisting of an extremely close pair of white dwarf (WD), neutron star (NS), and/or helium stars, are key to a better understanding of late-stage binary star evolution as well as alternate pathways to Type Ia supernovae (SN), the latter representing our best "standard candle" for determining the extra-galactic distance scale and the ultimate fate of the universe (e.g., cosmic acceleration). Galactic UCBs will also be routinely detected by the next generation of gravity wave telescopes like ESA/NASA's Laser Interferometer Space Antenna (LISA). A research team at Texas Tech University will analyze a fast cadence survey of the Galactic Plane in both hemispheres to identify a uniform sample of several-hundred new UCBs. The research will support a Ph.D. candidate. The principal investigator will also establish a program to bring research experience to underserved and rural elementary, middle, and high-school students plus teacher-training. UCBs can be detected through their light-curves, which show variations on timescales as short as <30-min due to eclipses or tidal deformation of the close components. The NSF-funded Zwicky Transient Facility (ZTF) and the BlackGEM array are the next generation optical time-domain surveys covering both hemispheres. This research will combine data from both with other large-scale surveys, such as eROSITA, PanSTARRS, Gaia, and SDSS-V to compile a uniform sample of Galactic plane UCBs. This project expects to find and characterize a few hundred new UCBs and anticipates the determination of accurate system parameter for a few tens of systems. The large sample will be used to challenge common envelope and binary evolution theories (e.g., predicted vs. observed orbital period and component mass distributions) and calculate empirical SN Ia rates for various pathways. They expect to triple the number of known LISA-detectable sources and increase the number of known SN Ia progenitors by at least an order of magnitude. UCBs are expected to dominate the sources detectable by LISA and will thus create a stochastic foreground gravitational wave signal. Characterizing the Galactic UCB population will be important in the near term for finding optimal design and data analysis methods for LISA to confidently detect other gravitational wave sources (e.g., binary blackhole or white dwarf mergers) hidden in this “noise”. This project thus advances the goals of the NSF Windows on the Universe Big Idea. 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.