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Below is an illustration of a neutron star accreting matter from a red giant star. The red giant (on the upper right) is expanding and dumping material onto the neutron star. This material forms a disk and then finally falls to the neutron star surface with a dramatic emission of X-rays, over ten thousand times more luminous than our sun! Neutron stars are the remnants of massive stars which have exhausted their nuclear fuel. They are unbelievably compact, with masses greater than our sun within a diameter of merely 20 kilometers. This is equivalent to a density of packing every person in the world into the volume of a sugar cube! For more amazing information about neutron stars check out this link.
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