The Mass of the Black Hole in the X-ray Binary M33 X-7 and the Evolutionary Status of M33 X-7 and IC 10 X-1

TL;DR

This study determines the mass of the black hole in M33 X-7 using radial-velocity analysis, shows such massive black holes can form in binaries, and explores their evolutionary paths and gravitational wave emissions.

Contribution

It provides the first detailed mass estimate of the black hole in M33 X-7 and models the evolutionary tracks of similar binary systems, highlighting their potential for gravitational wave detection.

Findings

Black hole in M33 X-7 has a mass of approximately 15.55 solar masses.

Massive black holes (≥15 solar masses) can form in binary systems.

Such systems are rare, with about one expected in M33.

Abstract

We have analyzed the observed radial-velocity curve for the X-ray binary M33 X-7 in a Roche model. We have analyzed the dependence between the component masses and the degree of filling of the optical star's Roche lobe to obtain the ratio of the masses of the optical star and compact object. For the most probable mass of the optical star, $m_v=70M_{\odot}$, the mass of the compact object is $m_x=15.55\pm3.20 M_{\odot}$. It has been shown that black holes with masses of $m_x=15M_{\odot}$ and even higher can form in binaries. We present characteristic evolutionary tracks for binary systems passing through an evolutionary stage with properties similar to M33 X-7 - type objects. According to population-synthesis analyses, such binaries should be present in galaxies with masses of at least $10^{11}M_{\odot}$. The present number of such systems in M33 should be of the order of unity. We have also studied the evolutionary status of the X-ray binary IC 10 X-1 with a Wolf-Rayet component, which may contain a massive black hole. The final stages of the evolution of the M33 X-7 and IC 10 X-1 systems should be accompanied by the radiation of gravitational waves.