A neutron star is the collapsed core of a large (10–29 solar masses) star. Neutron stars are the smallest and densest stars known to exist Though neutron stars typically have a radius on the order of 10 kilometres (6.2 mi), they can have masses of about twice that of the Sun. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past the white dwarf star density to that of atomic nuclei. Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons, which are subatomic particles with no net electrical charge and with slightly larger mass than protons. They are supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli exclusion principle. If the remnant has too great a density, something which occurs in excess of an upper limit of the size of neutron stars at 2–3 solar masses, it will continue collapsing to form a black hole.
Neutron stars that can be observed are very hot and typically have a surface temperature around 600000 K. They are so dense that a normal-sized matchbox containing neutron-star material would have a mass of approximately 3 billion tonnes, or a 0.5 cubic kilometre chunk of the Earth (a cube with edges of about 800 metres). Their magnetic fields are between 108 and 1015 times as strong as that of the Earth. The gravitational field at the neutron star’s surface is about 2×1011 times that of the Earth.
( little bit of maths )
The Earth’s radius is 3960 miles, whereas the neutron star’s radius is 6 miles. Divide 3960 by 6 to get 660. Then square 660 to obtain 435,600. Multiply 435,600 times 666,000 to find out that you’d weigh about 290,109,600,000 times more on a neutron star having twice the Sun’s mass but a radius of 6 miles.
( my weight is 128 kg right now so 128kg x 290,109,600,000 = 37,134,028,800,000 kg )
As the star’s core collapses, its rotation rate increases as a result of conservation of angular momentum, hence newly formed neutron stars rotate at up to several hundred times per second. Some neutron stars emit beams of electromagnetic radiation that make them detectable as pulsars. Indeed, the discovery of pulsars by Jocelyn Bell Burnell in 1967 was the first observational suggestion that neutron stars exist. The radiation from pulsars is thought to be primarily emitted from regions near their magnetic poles. If the magnetic poles do not coincide with the rotational axis of the neutron star, the emission beam will sweep the sky, and when seen from a distance, if the observer is somewhere in the path of the beam, it will appear as pulses of radiation coming from a fixed point in space (the so-called “lighthouse effect”). The fastest-spinning neutron star known is PSR J1748-2446ad, rotating at a rate of 716 times a second or 43,000 revolutions per minute, giving a linear speed at the surface on the order of 0.24 c (i.e. nearly a quarter the speed of light).
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