Students astonished by stuttering star

Pulsars are super-dense, highly magnetised balls of 'neutron matter' the size of a small city. They form when stars with more than 10 times the mass of our Sun explode as supernovae, leaving behind a compact remnant made of material far denser than ordinary matter. The name pulsar is given to these objects because they spin and emit pulses of radio waves.

Discovered in 1992, PSR J1717-4054 is around 15,000 light years away in the direction of the constellation of Scorpius (the Scorpion).

Early observations showed that its pulses would 'turn off', vanishing for hours at a time.

This intriguing behaviour made it a favourite in the PULSE@Parkes program, in which secondary school students use the Commonwealth Scientific and Industrial Research Organisation (CSIRO) 64-m Parkes radio telescope in eastern Australia to observe pulsars.

Students observed the pulsar 85 times between 2008 and this year.

"When the students looked at it, it was generally on or off. But sometimes, when it was on, it seemed to flicker. This prompted us to observe it for longer and with higher time resolution so that we could see individual pulses," said CSIRO's Dr Matthew Kerr, lead author of the new paper.

"The really weird thing is that it flickers in two different ways -- it has quick blips on and off, skipping one or two pulses, and longer stutters, when ten or more pulses go missing. The stutters are new and there really aren't any models that predict them," he said.

"If this pulsar were a human heart, we'd be recommending a pacemaker."

Thanks to the abundance of data gathered by the students, the pulsar's parameters have been well measured. "It's not obviously abnormal -- it looks like a run-of-the-mill pulsar," Dr Kerr said.

While several pulsars are known to 'null' -- turn on and off -- only two others show such varied behaviour as PSR J1717-4054.

More than 1000 students have taken part in PULSE@Parkes. Today's Monthly Notices paper is the first of many publications that will arise from the program.