The millisecond pulsar PSR J0437-4715 rotates 174 times per second but much of its characteristics have remained a mystery. Now, thanks to almost 30 years of observations from Murriyang, CSIRO’s Parkes radio telescope, we know its mass. And that’s the key to knowing so much more. In a series of three papers accepted for publication in Astrophysical Journal Letters, a global group of scientists describe how Murriyang together with NICER (Neutron Star Interior Composition ExploreR) have accurately measured the mass and radius of this nearby neutron star. NICER, NASA’s X-ray telescope on the International Space Station, studies neutron star interiors by detecting and mapping X-ray emission from million-degree hot spots on the surface of the star. Lead author Daniel Reardon has been observing this neutron star since he was a student ten years ago. “There were researchers studying the same pulsar with Murriyang for twenty years before me. It’s important that we have long-term data on the star to get accurate information,” he said. Radio data from Murriyang provided the mass of the pulsar, 1.4 solar masses. With the mass confirmed, the NICER team could then calculate an equatorial radius for the pulsar of 11.4 km from their data. This helps build a picture of the matter making up a neutron star. Neutron stars are some of the best laboratories for gaining new insights into fundamental nuclear physics, in conditions unobtainable on Earth. The image above shows an artist’s impression showing a companion white-dwarf star orbiting a pulsar. The dense companion warps the fabric of spacetime, compressing it, and delaying the pulses coming from the pulsar. (Image credit: Carl Knox/OzGrav)