Pulsars as Fantastic Objects and Probes

Pulsars are fantastic objects, which show the extreme states of matters and plasma physics not understood yet. Pulsars can be used as probes for the detection of interstellar medium and even the gravitational waves. Here I review the basic facts of pulsars which should attract students to choose pulsar studies as their future projects. Pulsars are sending us pulses – we can receive these pulses in radio bands. A small number of pulsars also emit high energy radiation in optical and X-ray or even γ-ray bands. Here let me discuss the radio pulsars, and leave the high energy emission and its explanation to Prof. Qiao in this volume. After the first pulsar discovered by Hewish et al. [1] in 1968, it was soon realized that they are rotating neutron stars [2, 3] with a diameter of only 20 km but extremely high density (10 15 g cm −3) and extremely strong magnetic fields (10 8 to 10 14 G). Because of revealing of this new state of matter in the universe, the pulsar discovery was awarded the Nobel Prize in 1974 in physics. Pulsars take birth in supernova explosion, which is evident from the young pulsars and supernova remnants associations [4]. For example, the Vela pulsar is located in the center of Vela nebula, the Crab pulsar is acting as the heart of Crab nebula. Pulsars get high velocity (a few 100 km s −1) [5, 6] in the explosion so that pulsars are running away quickly from their birthplace, even about half pulsars have escaped from our Galaxy in last 100 Myr [7]. The broadband radio emission of pulsars leaves from the emission region almost simultaneously. However, after these signals pass through the inter-stellar medium (ISM), the radio waves at a lower frequency, ν 1 , in GHz, come later than these at a higher frequency ν 2 , with a time delay of