Pulsar Timing

One of the endpoints for the evolution of massive stars (those at least ten times more massive than our Sun) is a neutron star. These extremely dense, rapidly rotating stars often contain as much as one solar mass worth of material spinning up to a few hundred times per second but with a radius of only 10 – 20 km.

Some neutron stars belong to a group known as pulsars which exhibit regular radio wave emission which we detect with each rotation of the object.

Figure 1: Variations in the period of PSR1257+12. 
Credit: D. Frail, A. Wolszczan (Nature Journal)

This regularity of radio emission helps astronomers; any deviation from this pattern might be attributable to the movement of this pulsar in an orbit with an exoplanet (see Figure 1). These systems of course may not be the most appropriate to search for life; they are highly magnetic objects and the planet would have had to have survived the process whereby the originally massive star became a pulsar by means of a supernova.

This method is extremely sensitive, allowing us to detect planets with as low a mass as 10% that of the Earth. Sadly, pulsars are fairly rare in our Galaxy and we might not expect such exotic environments to harbour too many planets.

However, this method gave us our first known exoplanet system. As detected by Aleksander Wolszczan and Dale Frail in 1992, we first learnt of exoplanets around PSR1257+12.

Go back to the main detection methods page.