Binary star systems, where two stars orbit one another while exchanging matter and influencing each other gravitationally, hold the key to unraveling cosmic mysteries. Among these, Cygnus X-3 stands out as an extraordinary and exotic example. Located 32,000 light-years away in the Cygnus constellation, this system comprises a massive Wolf-Rayet star and a black hole candidate (either a black hole or a neutron star, the former being more likely).
The Wolf-Rayet star in Cygnus X-3 ejects vast amounts of gas―equivalent to several Earth masses annually―while orbiting its black hole companion at an astonishingly close distance, completing a single orbit in less than five hours. This intense proximity creates a dynamic and turbulent environment. Gas falling into the black hole releases immense energy in X-rays―equivalent to several to ten days’ worth of the Sun’s energy in just one second. The emitted X-rays ionize the surrounding gas, forming what scientists call “photoionized plasma”.
In March 2024, the X-ray Imaging and Spectroscopy Mission (XRISM) observed Cygnus X-3 during a period of enhanced X-ray activity. XRISM’s cutting-edge spectrometer, Resolve, captured highly detailed data, revealing the movement of stellar winds and gas within the binary system. The data showed that the plasma near the black hole candidate moves at several hundred kilometers per second, demonstrating intense photoionization near the X-ray source.
Looking ahead, Cygnus X-3 is expected to undergo dramatic evolution: the Wolf-Rayet star will likely explode in a supernova, forming another black hole to create a binary black hole system, a known source of gravitational waves. XRISM’s observations promise to shed light on the formation and future evolution of this extraordinary cosmic pair, advancing our understanding of binary star dynamics and black hole physics.
These results will appear as XRISM Collaboration “The XRISM/Resolve view of the Fe K region of Cyg X-3” in the Astrophysical Journal Letters.
