Pulsars

SPACE

“ Pulsars are believed to form when supernovas compress the core of a massive star”

Secrets of pulsars

Find out everything you need to know about these amazing pulsing stars

From our perspective a pulsar is reminiscent of a lighthouse’s beam, with fl ashes of radiation viewed from Earth as the emission is pointed our way. These highly magnetised stars were fi rst discovered in 1967 as astronomers searched for a source for these regular pulsing lights from space that had no other explanation. Determined to be rotating neutron stars, pulsars are believed to form when supernovas compress the core of a massive star. They have the same angular momentum as the original star, but since they are much smaller, pulsars rotate at high speeds – some at hundreds of times a second! They emit beams of radiation along their magnetic axis, which is not the same as the rotational axis. For every rotation of the pulsar, the beam is seen once or twice (depending on its alignment with Earth), making it appear to fl ash. As its electromagnetic power is emitted, the pulsar’s rotation slows down and eventually stops pulsing. This seems to occur anywhere between 10-100 million years after the formation of the star.

One of the nearest pulsars to Earth is also one of the oldest to be detected with X-rays. An

isolated pulsar – meaning that it is not in a binary star or other system – PSR J0108-1431 is estimated to be about 200 million years old and about 770 light years away. Due to its age, J0108 is also one of the faintest, and spins only a little faster than one revolution per second. Pulsars have many different applications. Millisecond pulsars can rival the accuracy of atomic clocks, and may be used to detect gravitational waves that pass Earth. Pulsars have also been used to create maps that could be used in space. Such maps were included on the Pioneer and Voyager spacecrafts.

What happens when neutron stars collide?

1. Neutron stars have greater mass than the Sun, contained in spheres that are less than 29km (18mi) across. A collision between them lasts just 35 thousandths of a second.

4. Next, the new structure develops a black hole at its centre, surrounded by super-heated plasma. The black hole continues to draw in any material that ventures too close. 2. As you’d expect, mergers between these stars are chaotic. The merged magnetic fi elds that are created are a trillion times greater than that of our Sun.

5. The matter and the magnetic fi elds (shown here in the image in white) begin to organise. The matter takes on the formation of a high-energy plasma jet. 3. The stars become one swirling, dense and incredibly hot cloud of matter. Huge amounts of energy are released during this process, so much so that it’s visible from Earth.

6. The jet-like magnetic fi eld produces very short gamma-ray bursts – some of the brightest events in the universe. Satellites record these bursts almost every single day.

Crab Nebula in focus

The Crab Nebula, located in the Taurus constellation, contains the Crab Pulsar at its centre. Discovered in 1968, this pulsar is a very young neutron star about 20 kilometres (12.4 miles) across. It emits gamma rays through to radio waves, with a spin rate of about 30 times per second. It was the fi rst pulsar discovered to be the result of a supernova remnant. The nebula is very bright in X-rays and, with the exception of the pulsar, it’s considered to be very regular in spectrum and density. This means it’s often used as a calibration source in X-ray astronomy.