White Dwarfs Revealed in Gaia’s Candidate Compact Object Binaries

Abstract

Discovery and characterization of black holes (BHs), neutron stars (NSs), and white dwarfs (WDs) with detached luminous companions (LCs) in wide orbits are exciting because they are important test beds for dark remnant (DR) formation physics as well as binary stellar evolution models. Recently, 187 candidates have been identified from Gaia’s non-single star catalog as wide orbit (P orb/day > 45), detached binaries hosting DRs. We identify UV counterparts for 49 of these sources in the archival GALEX data. Modeling the observed spectral energy distribution (SED) spanning from the FUV-NUV to IR for these sources and stellar evolution models, we constrain the LC properties including mass, bolometric luminosity, and effective temperature for these 49 sources. Using the LC masses, and the astrometric mass function constrained by Gaia, we constrain the DR masses for these sources. We find that nine have masses clearly in the NS or BH mass range. Fifteen sources exhibit significant NUV excess and four show excess both in the FUV and NUV. The simplest explanation for these excess UV fluxes is that the DRs in these sources are WDs. Using SED modeling we constrain the effective temperature and bolometric luminosity for these 15 sources. Our estimated DR masses for all of these 15 sources are lower than the Chandrasekhar mass limit for WDs. Interestingly, five of these sources had been wrongly identified as NSs in the literature.

Modeling and Calibration of Gaia, Hipparcos, and Tycho-2 Astrometric Data for the Detection of Dark Companions

“…The techniques developed for exoplanet detection can also be applied in the search for dark companions such as black holes (e.g., El-Badry et al 2023), neutron stars (e.g., Shahaf et al 2023), white dwarfs (e.g., Ganguly et al 2023), and brown dwarfs (e.g., Feng et al 2022). Detecting these dark companions opens a new window to understanding the formation and evolution of massive stars and binaries (Heger et al 2003) and to test whether there is a 2-5 M e mass gap (Kreidberg et al 2012;Lam et al 2022;Ye & Fishbach 2022) between neutron stars and black holes.…”