Never Say Die
Pulsating dead stars
L-R: Pulsar, A neutron star that emits rapid and periodic pulses of radiation. A diagram of a pulsar showing its rotation axis, its magnetic axis, and its magnetic field
In 1967, a research student named Jocelyn Bell of Mullard Radio Astronomy Laboratory in Cambridge discovered a very mysterious noise coming from the sky. It consisted of very precise, short and rapid pulse of radio waves at regular intervals. She and her team locked down four of such cosmic sources and thought that the extra-terrestrials from a distant alien civilization were sending the Earthlings such systematic signals in an attempt to communicate with them. They were so sure of this explanation that they named these strange sources as LGM 1-4, where LGM stood for Little Green Men. But soon it was realized that these signals were actually coming from rotating neutron stars (the collapsed core of a supernovae, which takes place when the outer region of a star gets blown off in a tremendous explosion). And these neutron stars were emitting pulses of radio waves because of a complicated interaction between their magnetic fields and surrounding matter. The researchers later noticed that the signals coincided with the position of a flashing star located at the centre of the Crab Nebula, the very locale where the remnant of a supernovae that was seen from Earth in 1054 AD. A neutron star has the core of neutrons (the uncharged particles, very similar to proton) around which lies a fluid layer that is itself made up of neutrons, protons and electrons. The rotational power of the original star remains preserved in neutron star. As a result, the neutron star can spin very fast, between 1000 times and to even just once every single second. A neutron star is also very intense given the fact that a star's soriginal magnetic power is also condensed in it. What happens eventually is that, charged particles like protons and electrons are accelerated and get caught up by the neutron star's magnetic field and spin around to emit radio waves in narrow beams at the magnetic poles of the star. And when the rotational axis of such star is not aligned with the axis of the magnetic field, the beam of the radiation sweeps across the sky, delivering short radio waves. So far, hundreds of pulsars have been identified by astronomers worldwide. Crab Pulsar, one that was discovered by Jocelyn Bell, is perhaps the most carefully studied of all the known pulsars discovered so far. One of the most exceptional properties of this particular pulsar is that it emits radiation at all observable wavelengths, from radio wavelengths, through visible light to the highest-energy X-rays. It is believed that the younger the pulsar, the faster is its speed of rotation. Crab pulsar, formed a little over 900 years ago, rotates about 30 times per second whereas Vela pulsar, which is about 10,000 years old and found in a partially dispersed supernova remnant, rotates about 11 times per second. Scientists believe, pulsars will no longer be able to emit its radiation once its rotational rate dies out completely and eventually it'll shut off.
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