Observing a Cosmic Feeding Frenzy
Astronomers have leveraged the capabilities of the XRISM (X-ray Imaging and Spectroscopy Mission) spacecraft to conduct a detailed study of a neutron star as it consumes stellar winds from a massive hypergiant companion. This celestial interaction, located in the BP Crucis system roughly 13,000 light-years away, provides a rare look at how extreme stellar remnants acquire material.
The Nature of Neutron Stars
Neutron stars represent some of the most compact and extreme objects in the universe. Created after the collapse of massive stars, they pack the mass of one to two suns into a sphere only about 12 miles (20 kilometers) in diameter. The density is so intense that a single teaspoon of this material would possess a mass equivalent to approximately 10 million tons. Some of these objects, known as pulsars, rotate at extraordinary speeds—up to 700 times per second—while emitting powerful beams of radiation.
Analyzing the BP Crucis System
The system under investigation involves a pulsar named GX 301-2 and its donor star, Wray 977, a blue hypergiant approximately 40 times the mass of our sun. Due to its immense heat, the hypergiant constantly sheds a stream of ionized gas, or plasma. The neutron star, which orbits the hypergiant every 42 days and rotates on its axis every 11 minutes, moves through this plasma stream, triggering intense X-ray flares.
In February 2025, researchers focused the XRISM's Resolve instrument on the system for 16 hours to observe the aftermath of these flaring events. The data revealed that the plasma stream moves at roughly 335,000 miles per hour (540,000 kilometers per hour), exceeding the speed of an F-16 fighter jet by a factor of 200.
The Mechanics of Accretion
According to the research team, the process functions in distinct stages:
- Disk Formation: As the neutron star enters the stellar stream, its gravity draws plasma toward itself, establishing a dense, swirling disk of matter around the remnant. This material heats up as it funnels onto the star, generating X-rays.
- Disk Fragmentation: Upon reaching the densest part of the plasma river, the disk loses the necessary angular momentum to persist and begins to break apart.
- Direct Impact: With the disk disrupted, the plasma strikes the neutron star's surface directly, causing the most significant X-ray flares observed in the system.
Regarding the significance of these findings, Nazma Islam of the Manipal Center for Natural Sciences noted: «We could see how the dense stream of plasma acts very close to the neutron star.»
Brian Williams, NASA’s project scientist for the mission, highlighted the importance of the technology used: «The BP Crucis system is an ideal laboratory for studying wind-fed pulsar accretion, and XRISM's sensitive, high-resolution Resolve spectrometer is an ideal instrument for advancing our understanding of the processes involved.»
The findings were formally detailed in the journal Science Advances.