Pulsar timekeepers measure up to atomic clocks

Keeping time: using an array of pulsars to look for gravitational waves

An international team of astronomers has come up with a new way of keeping track of time by observing a collection of pulsars – rapidly rotating stars that emit radio pulses at very regular intervals. Although the ultimate goal of the research is to use pulsar timing to detect gravitational waves, the group has shown that the pulsar-based timescale can also be used to reveal inconsistencies in timescales based on atomic clocks.

Pulsars are neutron stars that rotate at very high speeds and appear to emit radio pulses at extremely regular intervals. The pulses are actually all we see of a radio beam that is focused by the star's magnetic field and swept around like a lighthouse beacon. Using a radio telescope, astronomers can measure the arrival times of successive pulses to a precision of 100 ns over a measurement time of about an hour. While this level of precision is significantly less than that offered by an atomic clock, pulsars could in principle be used to create timescales that are stable for decades, centuries or longer. This could be useful for identifying fluctuations in Earth-based timekeepers such as atomic or optical clocks, which normally do not operate over such long periods.
The team, which is led by George Hobbs at CSIRO Astronomy and Space Sciences in Australia, looked at data from the Parkes Pulsar Timing Array (PPTA) project. Using the Parkes radio telescope in Australia, the project aims to use a set of about 20 pulsars in different parts of the Milky Way to detect gravitational waves. The idea is that when a gravitational wave passes through our galaxy, its presence warps space/time such that the millisecond gaps between the pulses arriving from various pulsars are affected in a very specific way.

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 http://arxiv.org/abs/1208.3560
 http://physicsworld.com/cws/article/news/2012/aug/24/pulsar-timekeepers-measure-up-to-atomic-clocks