Pulsar Timing Arrays
  In the last decade, the use of an ensemble of radio pulsars to constrain the
characteristic strain caused by a stochastic gravitational wave background has
advanced the cause of detection of very low frequency gravitational waves
significantly. This electromagnetic means of gravitational wave detection,
called Pulsar Timing Array(PTA), is reviewed in this article. The principle of
operation of PTA, the current operating PTAs and their status is presented
along-with a discussion of the main challenges in the detection of
gravitational waves using PTA.
