Astronomers may have discovered a rare type of binary star system, where one star used to orbit inside its partner.
In the new study, astronomers investigated a pulsar known as PSR J1928+1815 located about 455 light-years from Earth. A pulsar is a kind of neutron star, a corpse of a large star that perished in a catastrophic explosion known as a supernova. The gravitational pull of the star's remains would have been strong enough to crush together protons and electrons to form neutrons, meaning a neutron star is mostly made of neutrons. That makes it very (very) dense.
