The weight of the largest diamond ever found on Earth was 3106 carats or 621 grams. However, outside our planet, according to astrophysicists, you can find and the diamonds are bigger — about a hundred times septillion. They are orbiting pulsars, or rotating neutron stars.
Neutron stars are cosmic bodies, consisting mainly of neutron nucleus (a neutron is a heavy elementary particle with no electrical charge). The average density of matter forming the star, many times greater than the density of an atomic nucleus, so the radius is only 10-20 kilometers, their mass is comparable to the mass of the Sun. In turn, pulsars, according to modern scientific ideas about them, are rotating neutron stars, the magnetic field which is inclined to the axis of rotation.
Although the first in the history of exoplanets (planets outside the Solar system) which was able to detect the astronomers, was found orbiting a pulsar (it is called PSR 1257+12), still the nature of such celestial bodies remains largely not understood, since a supernova explosion prior to the advent of neutron stars, was supposed to destroy or discard all the surrounding objects of similar size.
The researchers suggested that the heavenly bodies orbiting pulsars could be “fragments” of white dwarfs — stars, like our Sun, located at the final stage of its development. Based on this assumption, scientists have created a computer model and came to the conclusion that the likelihood of such a scenario is quite high. When this planet formed in this manner will consist mainly of carbon, and powerful gravity of the pulsar will provide enough pressure to make a diamond of unimaginable size.
Until that research is not published in any refereed scientific publications, however, it can be found on the website of preprints arXiv.org.