Weird neutron star is part of an unusual star system

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A pulsar whose behaviour could not easily be explained turns out to be part of an unusual dual system. This is the conclusion of research by Emma van der Wateren, who will be defending her PhD thesis at Radboud University on 10 June.

A pulsar is a neutron star that flashes with great regularity. "Neutron stars are really strange, compact spheres," explains astronomer Emma van der Wateren. "In terms of diameter, they are about the size of Utrecht - approximately 20 kilometres - with a mass 1.5 times that of the sun. So they are very small, but very heavy." The pulsar emits a beacon of light from two sides and is rotating. "That is why they are sometimes called the lighthouses of the universe. They are very reliable and thanks to those flashing beacons, you can measure if something is happening between that pulsar and Earth, like a gravitational wave."

Gigantic explosion

One of the research studies Van der Wateren conducted as part of her PhD was about a weird pulsar, discovered with LOFAR, the radio telescope in Drenthe. "This pulsar produced weird data and had a strange irregularity that could not be easily explained." The astronomer looked at the data and found that the pulsar in question is part of a double system, in which two stars - one of which is the pulsar - orbit each other. The two objects take decades to complete a single orbit, one of the longest orbital periods ever found for a pulsar. The companion star is an ordinary star of about 3.6 times the mass of the sun, which is a relatively low mass for such a system. "This is really remarkable, because it doesn’t make sense that these objects would still be in a dual system." A pulsar is created in a supernova explosion, which is so gigantic that you would expect these stars to fly far apart in the process. But that is not what happened in this case.

Van der Wateren: "The odds of this happening are really small, but we have shown that it is possible. In most cases, the stars will fly apart, but if you have just the right configuration, where the companion of the pulsar gets a push from the explosion in the right way, it can happen."

In the Radboud Science Snacks podcast, Emma van der Wateren explains in detail what a neutron star is and how we can use these stars to better understand the universe.