When objects as massive as these collide they create ripples in the fabric of space called gravitational waves. And it is these ripples that the researchers have detected.
The light from this supernova first reached Earth in July 1054 and was witnessed by astronomers in Japan and China.
When the star exploded, it formed a neutron star, which is the dense core of a star that is about the size of a city like Chicago. This became a pulsar, or rapidly spinning neutron star, that is now located in the nebula.
Neutron stars are the smallest in the universe, the remnants of supernovae. Their diameters are comparable to the size of a city like Chicago or Atlanta, but they are incredibly dense, with masses bigger than that of our sun. So think of the sun, compressed into a major city — and then think of two of them violently crashing into each other.