Why ‘cosmic clocks’ are not perfect

WASHINGTON - Scientists have taken a major step towards solving a 30-year-old puzzle: why the “cosmic clocks” called pulsars aren’t perfect.

CSIRO astronomer George Hobbs and colleagues in the UK, Germany and Canada, conducted the study by observing 366 pulsars collected over several decades with the 76-m radio telescope at the Jodrell Bank Observatory.

“We now have a more fundamental understanding of how pulsars work. We’ve shown that many pulsar characteristics are linked, because they have one underlying cause,” said Hobbs.

Armed with this understanding, astronomers will find it easier to compensate for errors in their pulsar “clocks” when they use them as tools - for instance, in trying to detect gravitational waves, which is something Hobbs is doing with CSIRO’s Parkes radio telescope.

The astronomers found that a pulsar’s magnetosphere switches back and forth between two different states.

“We don’t know exactly what happens,” said Hobbs.

“But one idea is that from time to time there is a surge of charged particles-electrons, for instance-whirling through the magnetosphere. Such a surge could apply the brakes a bit to the pulsar spin, and also affect the pulsar’s radio beam.”

The change in a pulsar’s magnetosphere shows up both in the shape of the radio pulses recorded on Earth and the pattern of the pulses’ arrival times.

“Pulsars are very stable timekeepers, but not perfect,” said lead author of the study, Dr Andrew Lyne.

“They have what we call ‘pulsar timing noise’, where the spin rate appears to wander around all over the place. This had baffled people for decades,” he added.

One of the aims of the study was to find an effective way to filter out this ‘timing noise’.

“We worked out how to do this, and along the way we were prompted to think hard about the nature of the timing noise,” said Hobbs.

The key advance was noticing that when the pulsar timing changed, so did the shape of the radio pulse.

“This ran against accepted thinking. Everyone had said they were unrelated. But we’ve shown they are,” said Hobbs.

Now astronomers can compensate for ‘timing noise’ by looking at the pulse shape change to spot when the pulsar magnetosphere has changed its state: this will show when the pulsar spin rate has also changed. (ANI)