Researchers discover one of the most massive neutron stars

Using a pioneering method, researchers from the Astronomy and Astrophysics Group of the UPC and the Canary Islands Institute of Astrophysics (IAC) have found a neutron star of about 2.3 solar masses—one of the most massive ever detected. The study was published on the 23rd of May in the Astrophysical Journal and opens a new path of knowledge in many fields of astrophysics and nuclear physics.

Neutron stars (often called pulsars) are stellar remnants that have reached the end of their evolutionary life: they result from the death of a star of between 10 and 30 solar masses. Despite their small size (about 20 kilometres in diameter), neutron stars have more mass than the sun, so they are extremely dense.

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Credit: G. Pérez-Díaz/IAC

The massive pulsar in the binary system PSR J2215+5135, illustrated in the figure, heats up the inner face of its companion star.

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PSR J2215+5135: Orbital period: 4.14 hours Spin period: 2.61 milliseconds Distance from Earth: about 10.000 light-years The inner face of the companion star, strongly irradiated by the pulsar, is heated up to about 8100 degrees Kelvin. As a consequence, hydrogen absorption lines dominate the visible spectrum of the hot side of the star. The outer face of the companion star is shielded from the pulsar wind, and remains at about 5700 degrees Kelvin.

As a consequence, magnesium absorption lines are stronger on its cold side. This allowed astronomers to measure the velocity of both sides of the companion, finding one of the most massive neutron stars known to date: about 2.3 times heavier than the Sun!