What happens after a star explodes? Does all the matter just disappear in the depths of space? Is there any remnant let behind to remind us that such an amazing structure had existed? Well, lucky for us there is something left from a star after it ends it life.
After a supernova, what remains from a massive star is what is called a neutron star. A neutron star is a spherical-like object with the radius of about 20 km and is held together by neutron degeneracy. That is the process in which the star becomes so dense in such a small amount of space that the atoms get so close to each other that they are almost touching, but since each neutron must have its own state, they almost repel each other which produces enough pressure to counteract with gravity, therefore preventing a possible black hole. What is so spectacular about this formation is, is that compared to 695,500 km radius of our Sun, this fairly small object has the mass of over 1.44 solar masses! Think about it, picture the mass of our Sun in something as small 12 miles! That means if you take a teaspoon full of a neutron star, it will way around a billion tons!
1.44 solar masses, also called Chandresekhar limit, is the line that determines if it a neutron star will develop or not. If the stellar mass is less than 1.44 solar masses, then there would not be enough mass to produce a neutron star but rather the star would be held by electron degeneracy. If the solar mass is 1.44 to 2 solar masses then the star will become a neutron star. However, if the solar mass is any bigger than 2 to 3 solar masses, there would be too much gravity pulling the star inward that not even neutron degeneracy will not be able to stop the collapse, making a black hole.
With a surface temperature of around 50,000 K, a neutron star has a crust made out of iron and electrons that is only 100 meters thick and with an atmosphere of about a couple of centimeters, yet because of it's high density, it has 10^11 times more gravity and stronger magnetic field than the Earth.
Pulsars are basically rotating neutron stars. Rotating at a speed of about 1000 rotations per second, particles are literally being ripped apart and shot out into space at around the speed of light which actually produces beams of light. So as the pulsar rotates, the light produced by the jet also rotates. This is why we call it a pulsar because on Earth, the star seems to be pulsing light. Pulsars emit X-rays and there have been some cases in which pulsars have been in a binary system in which 2 pulsars are orbiting around a common center of mass. There are about 40 binary pulsars found.
The closest pulsar to Earth is the star Calvera in the constellation Ursa Minor and is around 250 to 1,000 light years from us.
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