When a supernova occurs, it sometimes leaves a neutron star behind. These neutron stars spin extremely rapidly, producing radio waves that are sent out into the universe.

Those radio waves are compared to lighthouses in that they have a very consistent pulse to them, which is where they get the name pulsars.

Eventually, the pulsar slows down because the radiation it emits removes the energy from the system. In some cases, the emission of radio waves will stop altogether, but in other instances, the neutron star will have a main-sequence star near its orbit.

When that happens, the pulsar can pull material from the companion star, which provides it with the needed energy to accelerate the spin once again.

When this happens, it creates a millisecond pulsar (MSP). These have a faster spin than the original pulsar, and they are more reliable. In fact, they have such extremely reliable spin rates that they are often used as an astronomical timing device by astronomers.

So, when the pulsar PSR J1713+0747 experienced a change in its pulse rate, the astronomers were confused to say the least.

Every pulsar has its own unique ‘signature’ that has peaks in polarization and intensity. They occur multiple times per second, which allows astronomers to observe thousands of them, so they can chart the activity and develop what is called the stable integrated profile of that particular pulsar.

Macquarie University PhD student Rami Mandow said:

“Every now and then a few MSPs have shown the integrated profile changing, and it shouldn’t. […] The main peak of the profile has become narrower. The base (the lower quarter) has broadened. The polarization of the peak has also narrowed, while the base polarization broadened as well.”

Astronomers have not been able to figure out how or why there was such a dramatic change. It is orbited by a white dwarf, which is what was left over after the pulsar pulled away that star’s outer layers, allowing it to spin up to its rapid speed.

The astronomers, however, say that the white dwarf is too distant for it to have had this effect.

This change was so unexpected and unexplained that other astronomers have had to stop tracking it. Astronomers often track pulsars as part of their search for gravitational waves. Having this pulsar behaving so unusually means that the data they get from it can’t be used in that effort.

Mandow, however, is still interested in trying to figure out exactly what happened:

“My next project is looking at modelling PSR J1713+0747 so everyone can use the data post 2022.”

Whether he is successful or not, everyone can agree that this is a very unusual pulsar that needs more study. The paper published on the findings so far is available in open access in the Publications of the Astronomical Society of Australia.

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