New measurement for the stellar mass black hole in Cygnus X-1

Abstract

<p indent=0mm>The study on stellar mass black holes is an important issue in astrophysics. Over the past decades, astronomers have confirmed some stellar mass black holes and determined their physical properties via the observations of the X-ray binaries and the gravitational waves emitted from the mergers of binary black holes. Recently, a research team re-measured the precise distance of Cygnus X-1 (an X-ray binary) and subsequently derived the values of the mass, spin, and other properties of the black hole V1357 Cyg in Cygnus X-1. The results show that the mass of Cygnus X-1 is (21.2 ± 2.2) <italic>M</italic>_⊙, indicating that V1357 is the most massive stellar mass black hole in X-ray binaries, thus challenging the existing models of massive stellar binary evolution. The future precise measurements of similar black holes in X-ray binaries would further deepen our understanding of the stellar evolution models as well as the physical properties of stellar mass black holes.