An international team of scientists say a new  technique could turn pulsars into superbly accurate time-keepers.

A pulsar is the spinning, collapsed core of a massive star that ended in a supernova explosion and was first discovered in 1967.   A pulsar weighs more than our Sun but can be the size of New York City and produces beams of radio waves which sweep around the sky hundreds of times a second. Radio telescopes receive a regular train of pulses as the beam repeatedly crosses the Earth so that the object is observed as a pulsating radio signal.

The clock-like nature of the arrival times of these pulses means that pulsars have been used for the most precise studies of our understanding of the General Relativity theory of gravity. The best pulsars, called millisecond pulsars, are the fastest rotating and keep accurate time to a millionth of a second over a year.  The new work published in Science used the Lovell Telescope and they say it will improve studies of the origins of the Universe, including the search for gravitational  waves.  The discovery of gravitational waves, powerful ripples which have not yet 
been directly observed but were predicted by Einstein, could allow scientists to study violent events such as the merging of super-massive black holes and help understand the Universe shortly after its formation in the Big Bang.

The scientists used decades-long observations from the 76-m Lovell radio telescope at The University of Manchester's Jodrell Bank Observatory to track the radio signals of pulsars.   The extremely stable rotation of these cosmic fly-wheels has previously led to the discovery of the first planets orbiting other stars but this rotational stability is not perfect and slight irregularities in their spin have significantly reduced their usefulness as precision tools.

The team used observations from the Lovell telescope to explain these variations and to  demonstrate a method by which they may be corrected.   

University of Manchester Professor Andrew Lyne explains, "Mankind's best clocks all need corrections,  perhaps for the effects of changing temperature, atmospheric pressure, humidity or local magnetic field.  Here, we have found a potential means of correcting an astrophysical clock."

The rate at which all pulsars spin is known to be decreasing very slowly. What the team has found is that the deviations arise because there are actually two spin-down rates and not one, and that the pulsar switches between them, abruptly and rather unpredictably. 

These changes are associated with a change in the shape of the pulse, or tick, emitted by the pulsar.  Because of this, precision measurements of the pulse shape at any particular time indicate exactly what the slowdown rate is and allow the calculation of a "correction". This significantly improves their properties as clocks.

The results give a completely new insight into the extreme conditions near neutron stars and also offer the potential for improving already very precise experiments in gravitation. 

It is hoped that this new understanding of pulsar spin-down will improve the chances that the fastest spinning pulsars will be used to make the first direct detection of ripples, known as gravitational waves, in the fabric of space-time.   Many observatories around the world are attempting to use pulsars in order to detect the gravitational waves that are expected to be created by super-massive binary black holes in the Universe.  

With the new technique, the scientists may be able to reveal the gravitational wave signals that are currently hidden because of the irregularities in the pulsar rotation.