Chinese Astronomers Discover Record-Breaking Lightest Binary Neutron Star System with FAST

Par Wu Yuehui, People's Daily

A research team led by Han Jinlin at the National Astronomical Observatories of the Chinese Academy of Sciences has made a significant astronomical breakthrough using the ultra-high sensitivity of China's Five-hundred-meter Aperture Spherical Radio Telescope (FAST).

The team successfully detected pulsar J1856−0039, an exceptionally rare binary neutron star system featuring an ultra-short orbital period and the lowest total mass ever recorded for such a system.

Published recently in Physical Review Letters, the discovery stems from rigorous, precise observations. It offers a stringent test for general relativity while opening new avenues for studying extreme astrophysical phenomena, the nature of gravity, and the cosmic origins of heavy chemical elements.

Neutron stars are intensely dense stellar remnants born from the collapse of massive stars at the end of their life cycles. Because of their remarkably stable and precise rotations, astronomers often refer to them as cosmic clocks.

A binary neutron star system comprises two mutually orbiting neutron stars—a rare celestial configuration resulting from two successive supernova explosions. Over time, these systems emit gravitational waves, causing the two stars to spiral inward and eventually merge.

Scientists consider these systems vital cosmic laboratories. They serve as primary sources of heavy elements like gold and platinum, while offering unique environments to study matter under extreme densities and test the boundaries of general relativity.

As the world's most sensitive single-dish radio telescope, FAST brings unmatched capabilities to pulsar detection. Utilizing an innovative snapshot observing mode developed independently by Han's team, researchers have conducted a systematic, large-scale survey along the Galactic plane, uncovering approximately 900 new pulsars to date. Follow-up precision monitoring subsequently led to the identification of pulsar J1856-0039.

Data reveals that the system maintains an orbital period of just 2.36 hours, placing it among the tightest orbits ever observed in a binary neutron star system. This extreme proximity means the two stellar remnants orbit in a highly compact configuration, maximizing observable relativistic effects.

Furthermore, the system establishes a new benchmark for the lowest total mass recorded in a binary neutron star configuration. With a combined mass equivalent to just 2.488 solar masses, it is the lightest system of its kind discovered to date.

The visible pulsar possesses a mass of approximately 1.30 solar masses, while its neutron star companion weighs about 1.19 solar masses. This companion ranks among the lightest neutron stars globally, sitting close to the theoretical minimum mass limit and offering unprecedented insights into supernova physics.

根据 (According to) the team's dynamic modeling, the two neutron stars will inevitably merge in approximately 82 million years, likely forming a more massive single neutron star. This unique evolutionary timeline holds profound implications for understanding the equation of state governing matter inside neutron stars and tracing the cosmic genesis of precious heavy metals.

Han noted that by combining precise mass measurements with long-term monitoring, studies of binary pulsar systems can deliver crucial constraints to answer fundamental questions regarding spacetime gravity and ultra-dense matter.