Written by Neha Karl

A star with magnetic fields and beams coming out of it.

An artist’s impression of a pulsar giving off radio emissions.

Image: CSIRO

When your car runs out of fuel, it stops. But when a massive star runs out of fuel – it doesn’t just stop – it explodes!

An exploding star is called a supernova. The big blast can leave behind a pulsar, which is a kind of neutron star. A pulsar spins very fast and sends energy to Earth, in the form of radio waves. As the pulsar beam passes repeatedly over the Earth, like the spotlight of a lighthouse, the pulsar appears to be blinking.

A pulsar is sometimes known as the ‘clock’ of the universe. Just as the Earth spins on its axis every 24 hours, a pulsar spins at a constant speed. Scientists measure the speed of a pulsar by how often Earth receives a ‘pulse’ of radio waves.

With the help of CSIRO’s Parkes telescope, and another telescope in South Africa, a group of researchers noticed that one pulsar was spinning slower than usual. The pulsar is located in the constellation of Puppis and is estimated to be 37 000 light-years from Earth. One possible explanation for the decrease in speed is that a large rocky object – such as an asteroid – hit the pulsar. Scientists estimate that the asteroid weighed a billion tonnes and could have been created when the star exploded!

CSIRO’s Dr Ryan Shannon suggests that the pulsar may have reacted to the collision by zapping the asteroid, causing it to vaporise. The vaporised particles that are left behind are electrically charged. These particles cause the pulsar to spin more slowly, changing the shape of the radio waves received by Earth.

It has been said that time heals all wounds. The ‘clock’ of the universe is expected to return to its original spinning speed once those pesky particles pass!

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