XRISM Captures Unprecedented View of Cygnus X-3’s Gas Dynamics.

Cygnus X-3 is a high-mass binary system with a likely black hole and a hot Wolf-Rayet star. This artist’s concept depicts two gas components: a massive stellar wind from the star and a turbulent structure near the orbiting companion, potentially a wake. The black hole’s gravity captures some of the wind into an accretion disk, while jets of particles, moving near light speed, are emitted during outbursts.

 

The Japan-led XRISM (X-ray Imaging and Spectroscopy Mission) observatory has captured the most detailed portrait yet of gases flowing within Cygnus X-3, one of the most studied and enigmatic sources in the X-ray sky. This groundbreaking observation could provide crucial insights into the behavior of one of the universe’s most unusual binary systems.

Cygnus X-3 consists of a rare type of high-mass star—a Wolf-Rayet star—paired with a compact object, likely a black hole. “The nature of the massive star is one factor that makes Cygnus X-3 so intriguing,” explained Ralf Ballhausen, a postdoctoral associate at the University of Maryland and NASA’s Goddard Space Flight Center. “It’s a Wolf-Rayet star, which has evolved to the point where powerful stellar winds strip gas from its surface and drive it outward. The compact object interacts with this gas, heating it up and producing X-rays.”

A paper detailing the findings, led by Ballhausen, will appear in an upcoming edition of The Astrophysical Journal.

Cygnus X-3 has long been a target for X-ray telescopes, with its unique characteristics making it an ideal subject for XRISM’s cutting-edge capabilities. “For XRISM, Cygnus X-3 is a Goldilocks target—its brightness is ‘just right’ for the energy range where XRISM is especially sensitive,” said co-author Timothy Kallman, an astrophysicist at NASA Goddard. “It has been studied by every X-ray satellite ever flown, making it a rite of passage for new missions.”

XRISM, a collaboration between the Japan Aerospace Exploration Agency (JAXA) and NASA with contributions from the European Space Agency (ESA), features a microcalorimeter spectrometer called Resolve, which made this latest breakthrough possible.

In March 2024, Resolve observed Cygnus X-3 for 18 hours, capturing a high-resolution spectrum that allowed astronomers to examine the complex gas dynamics at play in the system. The data revealed a detailed picture of the outflowing gas from the hot Wolf-Rayet star, its interaction with the compact companion, and a turbulent region that could represent the wake produced by the companion as it orbits the gas stream. This binary system is so close that the two objects complete an orbit in just 4.8 hours.

XRISM’s Resolve instrument has captured the most detailed X-ray spectrum of Cygnus X-3 yet, revealing peaks from X-rays emitted by ionized gases and valleys where gases absorb X-rays. The spectrum, ranging from 2 to 8 keV, shows features from elements like sulfur, argon, and calcium, as well as detailed iron K-shell transitions. These high-resolution details, visible for the first time, will help astronomers refine their understanding of the system’s dynamics.

While Cygnus X-3 lies about 32,000 light-years away in the constellation Cygnus, its visibility is obscured by thick dust clouds in our galaxy’s plane. However, it has been observed across various wavelengths, including radio, infrared, gamma-ray, and X-ray light.

The gas in the system is ionized by X-rays from the compact companion, emitting and absorbing X-rays in ways that have been difficult to interpret. XRISM’s high-resolution spectrum revealed complex features that provide new clues about the system’s dynamics. For instance, the Doppler effect causes absorption valleys to shift to higher energies, indicating gas moving toward Earth at speeds of up to 930,000 mph (1.5 million kph), while emission peaks shift to lower energies, indicating gas moving away at slower speeds.

The detailed spectrum also revealed an unusual imbalance between absorption valleys and emission peaks. The team concluded that the dynamics of the stellar wind allow the moving gas to absorb a wider range of X-ray energies emitted by the companion. This analysis was made possible by XRISM’s ability to capture the system’s behavior across several orbits.

“A key to acquiring this detail was XRISM’s ability to monitor the system over the course of several orbits,” said Brian Williams, NASA’s project scientist for XRISM. “There’s still much to explore in this spectrum, and ultimately, we hope this data will help us determine if Cygnus X-3’s compact object is indeed a black hole.”

The findings could significantly advance our understanding of the physics governing these extreme environments. With XRISM’s high-resolution data, astronomers are one step closer to solving the mysteries of this fascinating binary system.