A rare binary star system has been discovered for the first time, consisting of a neutron star and a helium star that become partially eclipsed every few hours. This unique observation could provide valuable insights into the evolution of binary star systems.

While most stars in our galaxy exist in pairs, the formation and development of these binary systems remain poorly understood. Current theories suggest that when two stars orbit each other, one may expand to the point where its atmosphere envelops the other star. This phase of mass transfer causes the stars' orbit to shrink over approximately 1000 years, leading to either a merger or the ejection of the envelope.

In the case where one star is a neutron star, the envelope-ejection scenario is expected to result in a helium star and a rapidly spinning neutron star known as a millisecond pulsar. The helium star can periodically eclipse the pulsar, blocking its radio pulses from reaching Earth. While similar systems have been observed in dwarf galaxies, this is the first such binary system discovered in the Milky Way.

The pulsar, named PSR J1928+1815, was identified using the FAST radio Telescope during a survey of the Galactic Plane Pulsar Snapshot. Observations revealed a spin period of 10.55 ms, indicating recent acceleration due to mass accretion from its companion. Over four and a half years, researchers monitored the system at radio frequencies and determined an eccentricity of less than 3 × 10−5, indicating a nearly circular orbit with a short period of 3.6 hours.

The study also found an unusually high spin period derivative for a millisecond pulsar, indicating rapid energy loss as the pulsar slows down. This discovery supports long-standing theories of binary star evolution, shedding light on mass exchange, orbital shrinkage, and the ejection of shared envelopes. The system is expected to merge into a gravitational wave source in the future.

This groundbreaking observation provides a unique opportunity for astronomers to study the accretion and cooling processes of neutron stars, offering valuable insights into the evolution of compact star systems.

Source: Physics World