Formation pathways and survival of wide NS+MS binaries

Determine the evolutionary pathways and physical processes that allow binaries consisting of a solar-type main-sequence star and a dark companion with mass near 1.4 solar masses, as identified by Gaia DR3 astrometric solutions and radial-velocity follow-up, to avoid merger or dramatic orbital shrinkage during the red-supergiant phase of the neutron-star progenitor and to remain bound after neutron-star formation despite supernova mass loss and natal kicks.

Background

The paper reports 21 astrometric binaries with solar-type primaries and dark companions with masses near 1.4 solar masses, consistent with dormant neutron stars. Their orbits are wide (periods roughly 100–1000 days) and often eccentric, and the systems show properties suggestive of survival through both a red-supergiant phase and a supernova event.

The authors highlight that standard binary evolution would tend to lead to merger or strong orbital shrinkage during the red-supergiant phase and to binary disruption during the supernova due to mass loss and natal kicks. Understanding how these systems avoided both outcomes is central to explaining their formation history.

References

The formation history of these objects is puzzling: it is unclear both how the binaries escaped a merger or dramatic orbital shrinkage when the NS progenitors were red supergiants, and how they remained bound when the NSs formed.

— A population of neutron star candidates in wide orbits from Gaia astrometry  (2405.00089 - El-Badry et al., 2024) in Abstract

Whether such systems exist remains an open observational question. And if they do, would they be able to be detected with currently available observatories?

— Quiescent and Interacting Compact Remnant Binary Populations in the Space Telescope Era  (2608.27792 - Eastep et al., 28 Aug 2026) in Section 3.1, “Pre-interaction”