Like us, pulsars slow down as they age

U. SOUTHAMPTON (UK) — The spin of a pulsar slows down as it gets older and scientists have now developed a mathematical model to predict how the process develops in individual stars.

A pulsar is a highly magnetized rotating neutron star that forms from the remains of a supernova—an explosion which happens after a massive star runs out of nuclear fuel. A pulsar emits a rotating beam of electromagnetic radiation, rather like that of a lighthouse that can be detected by powerful telescopes when it points towards and sweeps past the Earth.

Pulsars rotate at very stable speeds, but as they emit radiation and lose energy, they begin to lose speed.


“A pulsar’s spin rate can be a very precise measurement of time which rivals the best atomic clocks, but in the end it will slow down,” says Professor Nils Andersson from the University of Southampton.

“Until now, the nature of this slowing hasn’t been well understood, despite 40 years of research. However, our model will open the door on this process—extending our knowledge of how pulsars’ operate and helping to predict how they will behave in the future.”

As a hot pulsar cools, its interior increasingly begins to turn superfluid—a state of matter which behaves like a fluid, but without a fluid’s friction or “viscosity.” It is this change of state which gradually affects the way that the star’s rotation slows down.

“The effect on the star’s rotation is like a figure skater extending their arms to slow their spin,” says Andersson’s colleague Wynn Ho. “Our model can explain the observed behavior of young pulsars, such as the 958-year-old pulsar in the Crab Nebula, which spins at 33 times a second.”

Published in Nature Physics, the findings have important implications for the next generation of radio telescopes being developed by large international collaborations, like the Square Kilometre Array (SKA) and the Low Frequency Array (LOFAR), of which Southampton is a UK partner university. The discovery and monitoring of many more pulsars is one of the key scientific goals of these projects.

Andersson and Ho’s mathematical model can be used in conjunction with these observations to predict how a pulsar’s rotation will change over time and allow scientists to peer inside these stars and explore their exotic composition.

“Our results provide a new method of linking the study of distant astronomical objects to laboratory work on Earth in both high-energy and low-temperature physics,” Andersson says. “It is an exciting example of interdisciplinary science.”

The research was supported by the Science and Technology Facilities Council.

Source: University of Southampton