Schematic view of a spinning star called a pulsar, which beams out rays of light like a lighthouse. Pulsars provide the most precise natural cosmic clocks known to date.
Credit: M. Kramer, MPIfR
Rapidly spinning stars that pulse over time could be used as the universes's most accurate clocks, thanks to a new discovery that helps explain how they rotate.
Astronomers have long hoped to use these stars, called pulsars, as time-keepers but slight irregularities in their spinning rates have so far prevented those plans. But a new understanding could enable scientists to compensate for it.
Pulsars are created when stars collapse and become so dense that protons and electrons squish together to become neutrons. After the star's mass is condensed into a small volume, conservation of angular momentum causes the pulsar to rotate extremely rapidly ? up to hundreds of revolutions per second.
Pulsars emit a steady ray of light that sweeps around like a lighthouse beam as they rotate ? thus, their light appears to pulse on and off as the beam crosses our line of sight.
This pulsing is almost perfectly steady ? but not quite. Slight variations in the observed puling rate have been unexplained, until now.
Timing the cosmos
A team led by astronomer Andrew Lyne of the University of Manchester in the United Kingdom used data from Lovell telescope at the university's Jodrell Bank Observatory to find that the deviations arise because the pulsars are slowly spinning down, and they are doing so at two different rates. The pulsars seem to switch between these spin-down rates abruptly and unpredictably.
Detailed measurements of a pulsar's light at any particular time should indicate what its slowdown rate is, and allow astronomers to calculate and apply a correction. That should greatly improve pulsars' usefulness as cosmic clocks.
"Mankind?s best clocks all need corrections, perhaps for the effects of changing temperature, atmospheric pressure, humidity or local magnetic field," Lyne said in a statement. "Here, we have found a potential means of correcting an astrophysical clock."
Ripples in space-time
Scientists hope that pulsar clocks can be applied to the question of gravitational waves. Einstein's theory of general relativity suggests that powerful events such as the merging of two supermassive black holes will create ripples in space-time that spread out through the universe.
These waves have never before been detected, but pulsars may be the key to finding them.
For example, if a gravitational wave passed through a pulsar, it would cause the pulsing rate to change. If these changes could be measured very accurately, scientists may be able to prove the existence of gravitational waves.
"Many observatories around the world are attempting to use pulsars in order to detect the gravitational waves that are expected to be created by supermassive binary black holes in the universe," said co-researcher Ingrid Stairs of the University of British Columbia. "With our new technique we may be able to reveal the gravitational wave signals that are currently hidden because of the irregularities in the pulsar rotation."
The researchers detailed their findings in a paper published online June 24 in the journal Science.
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