Neutron Star Wind Observations Challenge Space Physics Models

The X-Ray Imaging and Spectroscopy Mission, known as XRISM, has made a groundbreaking discovery regarding the winds emitted from a neutron star system called GX13+1. Observations from February 25, 2024, revealed that the outflow from this neutron star is unusually dense, contradicting existing models of how these cosmic winds form and interact with their environments.

Matteo Guainazzi, ESA XRISM project scientist, expressed the significance of this finding, stating, 'When we first saw the wealth of details in the data, we felt we were witnessing a game-changing result.' The neutron star GX13+1, a remnant of a once larger star, produces intense X-ray emissions due to an accretion disk composed of superheated material spiraling inward.

This disk can launch powerful outflows, influencing the surrounding space. The team focused on GX13+1 because its characteristics are thought to resemble those of supermassive black holes, which are known to produce similar outflows.

Astronomers use the term 'feedback' to describe the interaction of these winds with star formation, as they can compress molecular clouds leading to star birth or disperse them, halting star formation altogether.

The research team was particularly interested in GX13+1 as it unexpectedly brightened and reached or surpassed the Eddington limit just before their observations. This limit describes a threshold where the radiation pressure from infalling material can counteract further accretion onto the compact object.

The Resolve instrument on XRISM recorded GX13+1 during this dramatic phase, capturing unprecedented details of the outflow. Chris Done, lead researcher from Durham University, noted that the wind generated during this event was thicker than previously observed, despite its speed being relatively slow compared to winds near supermassive black holes.

While the wind from GX13+1 travels at about one million kilometers per hour, winds from supermassive black holes can reach speeds of 20 to 30 percent of light speed. This slow, dense wind challenges scientists' understanding, as earlier observations showed fast, clumpy winds from supermassive black holes at the Eddington limit.

The research team proposes that the temperature of the accretion disks around these objects could explain the differences in outflow characteristics. They suggest that the cooler disks surrounding supermassive black holes emit ultraviolet radiation, which interacts differently with matter compared to the X-ray emissions from neutron star systems.

If validated, this theory could reshape our understanding of energy and matter exchanges in extreme cosmic environments and their implications for galaxy evolution. The XRISM mission, launched on September 7, 2023, represents a collaboration between the Japan Aerospace Exploration Agency, NASA, and ESA, featuring advanced instruments designed to capture high-resolution X-ray data.