A Lack of Mass-Gap Compact Object Binaries in APOGEE

TL;DR

This study searches the APOGEE dataset for binary systems with potential compact object companions, finding none that likely host mass-gap neutron stars or black holes, thus highlighting the scarcity of such systems.

Contribution

The paper introduces a method to estimate companion masses in large stellar datasets and applies it to identify potential mass-gap compact objects, finding none.

Findings

No strong candidates for mass-gap NS or BH companions found.

Large binary sample identified with estimated companion masses.

Method demonstrates how to infer unseen companion masses from radial velocity data.

Abstract

Depending principally on mass, the compact object remnant left behind after a star's life may be a white dwarf (WD), neutron star (NS), or black hole (BH). While we have large samples of each of these remnants, we lack knowledge of the exact conditions separating these outcomes. The boundary between low-mass BHs and massive NSs is particularly poorly understood, as few objects between 2-5 $M_\odot$ are known. To probe this regime, we search the APOGEE DR17 dataset of 657,000 unique stars for binary systems with one stellar component that exhibit large radial velocity shifts over multiple observations. We identify 4751 likely binary systems, and estimate a minimum mass for each system's "invisible companion" under the assumption of tidal synchronization. Two systems have companion masses $\gtrsim$ 2 $M_\odot$, although we conclude that neither are good candidates for possessing a mass-gap NS or BH companions.