No signature of the orbital motion of a putative 70 solar mass black hole in LB-1

TL;DR

This study reanalyzes the LB-1 system and finds no evidence for a 70 solar mass black hole, suggesting previous mass estimates were based on stellar motion, not the black hole itself.

Contribution

It demonstrates that earlier claims of a massive black hole in LB-1 were based on misinterpreted stellar orbital motion, resolving tension with stellar evolution models.

Findings

No signature of the proposed massive black hole in LB-1.

Previous mass estimates were due to stellar motion, not the black hole.

The data does not support the existence of a 70 solar mass black hole.

Abstract

Liu et al. (2019) recently reported the detection of a 68 [+11/-13] solar mass (Msun) black hole (BH) paired with an 8.2 [+0.9/-1.2] Msun B-type sub-giant star in the 78.9-day spectroscopic binary system LB-1. Such a black hole is over twice as massive as any other known stellar-mass black hole with non-compact companions2 and its mass approaches those that result from BH-BH coalescences that are detected by gravitational wave interferometers. Its presence in a solar-like metallicity environment challenges conventional theories of massive binary evolution, stellar winds and core-collapse supernovae, so that more exotic scenarios seem to be needed to explain the existence and properties of LB-1. Here, we show that the observational diagnostics used to derive the BH mass results from the orbital motion of the B-type star, not that of the BH. As a consequence, no evidence for a massive BH remains in the data, therefore solving the existing tension with formation models of such a massive BH at solar metallicity and with theories of massive star evolution in general.