Are There Pre-Main-Sequence/Black Hole X-ray Binaries?

TL;DR

This study investigates whether pre-main-sequence stars can be donors in black hole low-mass X-ray binaries and finds that their properties do not match observed systems, suggesting they are unlikely hosts.

Contribution

The paper provides a detailed evolutionary analysis of pre-main-sequence stars in binaries with black holes, challenging the hypothesis that such stars are the donors in observed BHLMXBs.

Findings

Pre-MS stars generally do not synchronize with the orbit due to slow rotation.

Mass transfer occurs only for stars >1.2 solar masses after nuclear expansion.

Predicted temperatures and periods do not match observed BHLMXBs.

Abstract

A large fraction of black hole low-mass X-ray binaries (BHLMXBs) are in short period orbits, which require strong orbital angular momentum loss during the previous evolutionary stage. Ivanova (2006) put forward the possibility that some of the BHLMXBs may harbour pre-main-sequence (MS) donor stars, in order to explain the Li-overabundances in three BHLMXBs. In this work we investigate the evolution of low-mass pre-MS stars in binaries with a BH companion. We calculate the evolution of the spin and orbital periods, the stellar radius and the Roche-lobe radius during the pre-MS stage with the stellar evolution code MESA. We find that, because of the relatively slow rotation of the pre-MS star after the common envelope evolution and the long turnover time in the pre-MS stars, tidal torque is not always able to synchronize the pre-MS star, so the spin periods are generally longer than the orbital periods. Mass transfer can occur only for stars with mass larger than $\sim 1.2M_\odot$, which experience expansion due to nuclear reaction after the Hayashi contraction phase. The effective temperatures and orbital periods of these systems do not match the observations of BHLMXBs. Our results show that the observed BHLMXBs with lithium overabundances are unlikely to host pre-main sequence donor stars.