What is Neutron star?
[[File:PIA18848-PSRB1509-58-ChandraXRay-WiseIR-20141023.jpg|thumb|right|280px|Radiation from the [[pulsar]] [[PSR B1509-58]], a rapidly spinning neutron star, makes nearby gas glow in [[X-ray]]s (gold, from [[Chandra X-ray Observatory|Chandra]]) and illuminates the rest of the [[nebula]], here seen in [[infrared]] (blue and red, from [[Wide-field Infrared Survey Explorer|WISE]])]] [[File:Neutron star cross section-en.svg|thumb|250px|A model that shows what a neutron star would look like on the inside section.]] A '''neutron star''' is a very small and [[dense]] star made almost completely of [[neutrons]]. They are [[compact star|small stars]] with a [[radius]] of about 11{{ndash}}11.5 [[kilometres]]. They have a [[mass]] of about twice that of the [[Sun]]. They are the smallest and densest stars known to exist in the [[Universe]].<ref>{{cite book |title=Compact stars: nuclear physics, particle physics and general relativity |edition=illustrated |last=Glendenning, Norman K. 2012 |date=6 December 2012 |publisher=Springer |isbn=978-1-4684-0491-3 |page=1 |url=https://books.google.com/books?id=cCDlBwAAQBAJ}} [https://books.google.com/books?id=cCDlBwAAQBAJ&pg=PA1 Extract of page 1]</ref> They are what is left of a huge star which exploded as a [[supernova]]. The [[density]] of the star is like that of the [[nucleus (physics)|nucleus]] of an [[atom]]. They have strong [[magnetic field]]s, between 10<sup>8</sup> and 10<sup>15</sup> times as strong as that of [[Earth]]. The [[gravitational field]] at the neutron star's surface is about 2×10<sup>11</sup> times stronger than on Earth. To imagine how dense a neutron star is, take all of the mass of our [[sun]] (which has a [[diameter]] of {{convert|1392000|km|mi}}) and push it down into a size that would fit into a ball with a {{convert|19|km|mi}} diameter. Another way to understand the density is this: one teaspoon of matter from the neutron star would weigh 6 billion tons. Neutron stars spin very fast, from 0.001 second up to 30 seconds to turn. They come in different