Supernovae are vital for the chemical evolution of the Universe. Not only are they the end-points in the lives of all massive stars, but they provide the means by which the chemical elements formed in the cores of those stars are dispersed into space, ready to be incorporated into future generations of stars and planets. Every atom of iron in your blood was formed in the heart of an ancient star and thrown into space by a supernova long before the Earth was formed.

The objects left behind by supernova explosions are also interesting in their own right. Typically, a supernova will result in the core of the exploded star collapsing to become a super-dense neutron star. Astronomers know of over a thousand neutron stars scattered throughout the Galaxy, observed as radio pulsars sending out their regular beams of radiation, like interstellar light houses.

Many (perhaps most) stars in the Galaxy though are born in pairs, as components of binary star systems. If the binary survives the supernova explosion of the first star in the pair to evolve, what emerges may be a so-called X-ray binary star.

In these compact binary systems, the neutron star is able to pull material off its less evolved companion, thanks to its immense gravity, as they orbit around each other. That transferred material will crash down onto the neutron star surface, heating up enormously as it does so.

The super-heated plasma is so hot it can emit X-rays which are detected by space-based X-ray telescopes. Hundreds of these X-ray binary stars are observed throughout the Galaxy, and indeed in nearby galaxies too.
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