China's FAST Telescope Finds a Millisecond Pulsar in an Almost Perfectly Circular Orbit, a Rare Window Into Binary Evolution
PSR J1810-0623 spins 220 times a second and circles a white dwarf every 15.4 days on an orbit with an eccentricity of just 0.000015, one of the roundest pulsar binaries known.
Overview
Astronomers using China’s Five-hundred-meter Aperture Spherical radio Telescope (FAST) have discovered a millisecond pulsar locked in an almost perfectly circular orbit around a white dwarf, a configuration so rare that it offers a fresh testing ground for theories of how binary star systems evolve. The pulsar, designated PSR J1810-0623, has a rotation period of just 4.55 milliseconds, meaning it spins about 220 times every second, according to a Science China Press release distributed via EurekAlert. The discovery was published in the journal Science China Physics, Mechanics & Astronomy.
What We Know
The defining feature of the system is the near-perfect roundness of its orbit. The pulsar and its companion circle their common center of mass every 15.4 days, and the eccentricity of that orbit is only about 0.000015 — “an orbit so close to circular that its elliptical shape is almost undetectable,” the release states. That makes it rounder than almost any comparable system known, even beating the celebrated PSR J1614-2230, as Universe Today reported.
The companion star has a mass of about 0.64 times that of the Sun and is likely a carbon-oxygen white dwarf, per the release. FAST, described by Universe Today as “the largest single dish radio telescope on Earth, a vast bowl nestled into a natural hollow in the hills of southwest China,” tracked the system through precise observations spanning six and a half years.
Those observations revealed that the pulsar has undergone an extremely thorough recycling process. Most millisecond pulsars are not born spinning so fast; they are accelerated over time as a companion star feeds them material. As the release describes it, “material from the companion star falls onto the neutron star, transferring angular momentum and causing it to spin faster.” Universe Today likened the mechanism to “spinning a bicycle wheel by feeding a belt onto its rim,” noting that PSR J1810-0623 “has been recycled with remarkable thoroughness.”
The pulsar was likely born in what the release calls a “moderate-mass X-ray binary system,” where the companion continuously transferred material over vast stretches of time. A sign of the system’s age is the pulsar’s surface magnetic field, which the release says “has also decayed to only about 100 million Gauss” — weak by neutron-star standards.
Beyond charting the binary’s history, the team used the polarization properties of the pulsar’s radio signals to measure magnetic field information along the line of sight, the release notes, adding data points useful for mapping the structure of the Milky Way’s magnetic field.
Why It Matters
This kind of formation pathway is uncommon in the Milky Way, which is precisely what makes the system valuable. The release frames PSR J1810-0623 as “providing a new observational benchmark for testing binary evolution theories.” Because its orbit is so clean and its parameters so well constrained, astronomers can use the system, as Universe Today puts it, “as a natural laboratory to weigh the neutron star, test theories of how binaries evolve, and even probe gravity itself.”
What We Don’t Know
The companion’s identification as a carbon-oxygen white dwarf rests on observational calculations of its mass rather than a direct optical detection, and the release describes it only as the “likely” nature of the star. The full research team beyond the listed expert contact, Jie Zhang of the School of Arts and Sciences at Shanghai Dianji University, is not enumerated in the public materials, and the underlying paper carries technical details — precise timing measurements, mass functions, and the dispersion and rotation measures behind the magnetic-field mapping — that lie beyond what the press summaries report.