Astronomy

Facts about Pulsars



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The life of a pulsar

Once upon a time the universe was thought to be a serene and peaceful place where nothing interesting was happening, unchanged and perfect. That was the time when religion ruled over humans knowledge. Then science happened and with it marvellous things came to life. One of those things was a mysterious object, very small in size with a strong magnetic field that emits X-rays at intervals so precise that at one time it was thought to be a beacon used by some advanced civilisation to guide possible star ships around the galaxy. However this is a far more exciting object than a beacon, it's the remnant of star and it's called pulsar.

Stars comes in all sizes, from brown dwarfs 1/10 the mass of our sun to blue giants as massive as 100.000 suns. A different mass means the star will die in a different way, the smallest one will just become colder and less bright and very slowly disappear from view while the biggest ones will die a lot sooner and in a much more spectacular way. For stars that are bigger than our sun but smaller than 9 solar masses the end will come with a spectacular explosion that will be bright enough to outshine the galaxy they reside in for a few days. However this class of stars are not big enough for the core of the star to disappear as a black hole. While the outer layers of the star will blow up and form a planetary nebula the core, usually made of iron (iron is the last stage of nuclear fusion) will do the exact opposite, it will implode squashing the atoms with such force that a core that was as big as Saturn will be compressed into just few miles while virtually losing no mass at all. Under such forces atoms cannot exist, they are compressed so densely that electromagnetism is no longer the dominant force. The weak force takes over and transform electrons and proton into neutrons and so a neutron star is formed. Because the mass of the star is virtually the same it's gravitational field is also the same, just concentrated into a smaller area. A teaspoon of matter of a neutron star would weight few tonnes while a light beam passing too close to the star will be bent according to relativity forming, when the relative positions are right, the phenomenon known as gravitational lensing. Gravitational lensing occurs when light from a source behind a massive gravitational field is bent and pass around the source of the gravitational field using more than one path. The end result is a number of identical images appearing on 2, sometimes 4 sides of the pulsar.

Pulsar are known to rotate very fast, in the order of thousands of times a minute, this so because the momentum of the star is transferred to the pulsar, the pulsar being so much smaller it has to rotate so much faster to conserve the initialmomentum. However the most important characteristic of a pulsar is the regularity of which it emits X-rays from it's polarregions. It is as reliable as the most advanced nuclear clock and it will continue to work for as long as it exists. Pulsar are one of the tools used by astronomers to calculate the distances between galaxies. Pulsars are one of the most visually stunning and interesting celestial bodies in the universe, however they are also one of the last place you want to go on a vacation to, the strong gravity will rip you to bits while the intense X-ray radiation will cook you in the crispiest way possible.

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More about this author: Roberto Chiodetti

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