Researchers Disprove Pulsar Glitch Theory
December 18, 2012

Researchers Disprove Pulsar Glitch Theory

Lee Rannals for — Your Universe Online

Researchers reported in the journal Physical Review Letters that they have found a "glitch" in a 40-year-old theory explaining the periodic speeding up or "glitching" of pulsars.

Pulsars emit a rotating beam of electromagnetic radiation, which can be detected by powerful telescopes once it sweeps past the Earth.

The cosmic objects, which are highly magnetized rotating neutron stars formed from the remains of supernovae, rotate at extremely stable speeds. Despite the stability, the pulsars still occasionally speed up in brief events described as "glitches."

One theory suggests that these events come up as a rapidly spinning superfluid within the star that transfers rotational energy to the star's crust. However, University of Southampton researchers used a mathematical model to disprove this theory.

They found that the amount of superfluid in the crust cannot explain the changes in angular momentum required to account for the glitches.

"Imagine the pulsar as a bowl of soup, with the bowl spinning at one speed and the soup spinning faster," Professor Nils Andersson said in a statement. "Friction between the surface of the bowl and its contents, the soup, will cause the bowl to speed up. The more soup there is, the faster the bowl will be made to rotate."

He said that this analogy helps to describe the concept behind the accepted theory of why pulsars suddenly increase speed.

"However, our research shows that these pulsar glitches are too large to be explained in this way," Andersson said. "The amount of superfluid, or 'soup', available in the crust of a pulsar is too small to cause the kind of friction needed to create this effect."

The researchers said an important ingredient is the effective neutron mass in the superfluid, which might be very large, according to a paper reported in the same journal by Nicholas Chamel of the Free University of Brussels.

In the previous paper by Chamel, he arrived at a similar conclusion to the Southampton team, saying that the crust superfluid is not enough to explain the data.

The team used their calculations, along with data from radio telescopes and results from nuclear physics theory, to challenge the pulsar glitch theory.