What happens in the Cygnus X-3 star system?

New observations made from space and an in-depth analysis of them have allowed us to reveal details of the chaos prevailing in the Cygnus X-3 star system, located about 32,000 light-years from Earth.

The analysis was carried out by a team including Ralf Ballhausen and Timothy Kallman, both from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, United States. The observations were made using the XRISM (X-Ray Imaging and Spectroscopy Mission) astronomical satellite of the Japan Aerospace Exploration Agency (JAXA), a mission that has had the collaboration of NASA and that began with the launch of the ship in 2023.

Cygnus X-3 is a binary system composed of a high-mass star of an unusual type and a compact companion, probably a black hole.

The nature of the massive star is one of the factors that makes Cygnus X-3 so intriguing. It is a Wolf-Rayet type star, a star that has evolved to the point where its outflows called stellar winds are so strong that they tear gas from the surface of the star and expel it outward. The compact object sweeps up and heats some of this gas, causing it to emit X-rays.

In Cygnus X-3, the star and the compact object are so close that they complete a mutual orbit in just 4.8 hours.

Although the thick dust clouds in the central plane of our galaxy obscure the visible band light from Cygnus X-3, this binary system has been studied in radio waves, in the infrared band and in gamma rays, as well as in X-rays. .

The system is immersed in the star’s gas cloud, a cloud that is illuminated and ionized by X-rays from the compact companion. The gas emits and absorbs X-rays, and many of the prominent peaks and valleys in the spectrum incorporate both aspects. Previous attempts to understand the spectrum have encountered anomalies in which many traits appear to be in the wrong place on the spectrum.

The explanation that clarifies these anomalies is that, through the action of the Doppler effect, the rapid movement of the gas displaces these features outside the locations that are usual in comparable spectra. Absorption valleys typically shift toward higher energies, indicating that the gas is moving toward us at speeds of up to 1.5 million kilometers per hour. The emission peaks shift towards lower energies, which indicates that in these cases the gas is moving away from us.

Cygnus X-3 is a high-mass binary star formed by a compact object (probably a black hole) and a Wolf-Rayet star. This artistic recreation shows an interpretation of the system. High-resolution X-ray spectroscopy indicates the existence of two gaseous components. One of them is a strong outflow, or wind, that emanates from the massive star and forms a background. The other is a turbulent structure (perhaps a wind-carved wake) located near the compact companion. As shown here, a black hole’s gravity captures some of the wind in an accretion disk around it, and the disk’s orbital motion sculpts a path (yellow arc) through the gas flow. The companion emits jets of particles moving at near the speed of light, as seen here, that extend above and below the black hole. (Image: NASA’s Goddard Space Flight Center)

Some spectral features of the Cygnus X-3 system show absorption troughs much more intense than the emission peaks. The reason for this imbalance, the team concludes, is that the dynamics of the stellar wind allow the moving gas to absorb a wider range of X-ray energies emitted by the companion. (Fountain: NCYT by Amazings)