A population of neutron star candidates in wide orbits from Gaia astrometry

• DOI: 10.33232/001c.121261
• Publication Date: 2024-07-15T08:34:42Z
• Authors: Kareem El-Badry; Hans-Walter Rix; David W. Latham; Sahar Shahaf; Tsevi Mazeh; Allyson Bieryla; Lars A. Buchhave; René Andrae; Natsuko Yamaguchi; Howard Isaacson; Andrew W. Howard; Alessandro Savino; Ilya V. Ilyin
• Keywords: Astrometry; Star (game theory)

We report discovery and spectroscopic follow-up of 21 astrometric binaries containing solar-type stars dark companions with masses near 1.4 $M_{\odot}$. The simplest interpretation is that the are dormant neutron (NSs), though ultramassive white dwarfs (WDs) tight WD+WD cannot be fully excluded. selected targets from Gaia DR3 binary solutions in which luminous star on main sequence dynamically-implied mass unseen companion (a) more than $1.25\,M_{\odot}$ (b) too high to any non-degenerate or close binary. obtained multi-epoch radial velocities (RVs) over a period 700 days, spanning majority orbits' dynamic range RV. RVs broadly validate significantly tighten constraints masses. Several systems have unambiguously above Chandrasekhar limit, while rest between 1.25 orbits eccentric at fixed those typical WD + MS binaries, perhaps due natal kicks. Metal-poor overrepresented sample: 3 out objects (14%) [Fe/H]$\sim-1.5$ halo orbits, compared $\sim$0.5% parent sample. metal-poor all strongly enhanced lithium. formation history these puzzling: it unclear both how escaped merger dramatic orbital shrinkage when NS progenitors were red supergiants, they remained bound NSs formed. has now discovered black holes (BHs) 9 $M_{\odot}$, $1.4\,M_{\odot}$. lack intermediate-mass this sample striking, supporting existence BH/NS bimodality 4 orders magnitude period.