Pulsars are ultra-dense neutron stars left behind after massive stars explode. They spin at incredible speeds, emitting regular beams of electromagnetic radiation. When these beams sweep past Earth, astronomers detect periodic signals, much like flashes from a lighthouse.
Recently, China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) — has discovered a new pulsar of significant research value, named PSR J1810−0623. This pulsar not only spins extremely fast, but its formation history also appears to record a long and complex "binary evolution story."
PSR J1810−0623 has a rotation period of just 4.55 milliseconds, meaning it spins about 220 times every second. Astronomers believe that the vast majority of millisecond pulsars are not born spinning this fast; rather, they are accelerated through long-term interactions with a companion star: material from the companion star falls onto the neutron star, transferring angular momentum and causing it to spin faster and faster. This process is known as "recycling." Through precise observations spanning six and a half years, the research team found that PSR J1810−0623 has undergone an extremely thorough recycling process. Not only is its rotation speed exceptionally high, but its surface magnetic field has also decayed to only about 100 million Gauss.
PSR J1810−0623 has a companion star, and the two orbit their common center of mass every 15.4 days. Based on observational calculations, this companion star has a mass of about 0.64 times that of the Sun and is likely a carbon-oxygen white dwarf. This clue reveals the origin of PSR J1810−0623: it was likely born in a "moderate-mass X-ray binary system". Over vast stretches of time, the companion star continuously transferred material to the neutron star, not only causing the latter to spin rapidly but also eventually depleting its own outer layers, leaving behind the white dwarf remnant we see today. This formation pathway is uncommon in the Milky Way, making such systems particularly valuable.
What particularly intrigues researchers is that the orbit of this binary system is nearly a perfect circle. The eccentricity of PSR J1810−0623's orbit is only about 0.000015, representing an orbit so close to circular that its elliptical shape is almost undetectable. Generally, long-term, stable mass transfer between binary stars gradually smooths out orbital irregularities, making the orbit increasingly circular. This characteristic is similar to a few known special systems, such as the famous PSR J1614−2230. However, the orbit of PSR J1810−0623 is even rounder, providing a new observational benchmark for testing binary evolution theories.
Beyond revealing binary evolution processes, this newly discovered pulsar can also help scientists study the Milky Way itself. The research team used the polarization properties of its radio signals to measure magnetic field information along the line of sight, thereby providing new data points for mapping the Galactic magnetic field structure.
In the future, as FAST and other radio telescopes continue long-term timing observations, scientists hope to further determine the true mass of this neutron star and even test gravitational theories through more precise orbital measurements. For studying pulsar recycling mechanisms, binary system evolution, and the structure of the Milky Way, PSR J1810−0623 will prove to be an immensely valuable "natural laboratory".
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