About 14 other supernova remnants are scattered throughout our galaxy, and occur in other galaxies, too. In 1885, a supernova in the nearby Andromeda galaxy briefly doubled that galaxy's brightness. More than 700 have been recorded in other galaxies . The force of gravity causes electrons and protons to coalesce and form neutrons. In the absence of electrical forces and electron degeneracy pressure, the core collapses to a state of dense neutron matter .
Neutron stars are truly remarkable objects.
The matter is the densest in the observable universe. For decades, astrophysicists talked about neutron stars, but, no known observational technique could detect them , and no one could prove they existed. But in November 1967, a 4.5-acre array of radio telescopes in England detected a strange new type of radio source in the sky. These pulsing radio sources came to be called pulsars . The mysterious pulsars turned out to be the long-sought neutron stars.