Pulsars

Pulsars are rotating derivatives of neutron stars, with pulses of radiation being emitted on two of its opposite ends. When a neutron star has a fast enough speed of rotation and strong enough magnetic field, it becomes a pulsar.

 From the earth, when seen through radio telescopes, they appear to flicker. 

Why?

The emitting radiation beam is not aligned to its axis, as you can see in the thumbnail. When the beams come towards the line of sight of the telescope, a light pulse is visible. When they move away, the light turns off. Hence, the flicker effect. This effect helps us to know how fast the pulsar is spinning. 

Now, why are pulsars important?

Pulsars are used to study extreme states of matter, search for exoplanets and measure distances. Also, Einstein's theory of gravitational waves was confirmed in 2017, 100 years after he proposed it, using a binary pulsar.