Detecting Stripped Stars While Searching for Quiescent Black Holes

TL;DR

This paper discusses the challenge of identifying quiescent black holes in binary systems, highlighting the importance of recognizing stripped stars that can mimic black hole companions in spectroscopic surveys.

Contribution

It emphasizes the need to distinguish stripped stars from true black hole companions to improve detection accuracy in large spectroscopic studies.

Findings

Stripped stars can mimic black hole companions in binary systems.

Some B-type stars are actually stripped stars, not black hole hosts.

Recognizing stripped stars is crucial for accurate black hole detection.

Abstract

While the number of stellar-mass black holes detected in X-rays or as gravitational wave sources is steadily increasing, the known population remains orders of magnitude smaller than predicted by stellar evolution theory. A significant fraction of stellar-mass black holes is expected to hide in X-ray-quiet binaries where they are paired with a "normal" star. Although a handful of such quiescent black hole candidates have been proposed, the majority have been challenged by follow-up investigations. A confusion that emerged recently concerns binary systems that appear to contain a normal B-type star with an unseen companion, believed to be a black hole. On closer inspection, some of these seemingly normal B-type stars instead turn out to be stars stripped of most of their mass through an interaction with their binary companion, which in at least two cases is a rapidly rotating star rather than a compact object. These contaminants in the search for quiescent black holes are themselves extremely interesting objects as they represent a rare phase of binary evolution, and should be given special attention when searching for binaries hosting black holes in large spectroscopic studies.