Pulsar caught in evolutionary change

This animation represents the evolutionary process of a pulsar as it swings between X-ray and radio emission. The pulsar (left) is in a binary system with a low-mass star as a companion (right). The two objects orbit around their mutual centre of gravity; for clarity, this motion is not shown in the animation.

At the beginning of the animation, the pulsar spins very fast emitting two narrow beams of radio waves (shown in purple). Over several million years this rotation gradually slows down. Eventually, the gravitational pull of the pulsar starts drawing matter from the companion star. As the pulsar accretes matter via an accretion disc, it gains angular momentum and its rotation becomes extremely rapid again.

During the accretion process, the high density of accreted matter damps out the radio emission and is seen only in X-rays (shown as wide, white beams). When the accretion rate decreases, the pulsar’s magnetosphere expands and pushes matter away. As a consequence, the X-ray emission becomes weaker, while the radio emission intensifies.

The pulsar swings back and forth between the two states several times over several hundreds of millions of years until it final slows down to become a purely radio-emitting pulsar, while its companion star has evolved into a white dwarf.

Read more: Missing link found between X-ray and radio pulsars