The universe is estimated to contain around 10^22 to 10^24 neutron stars.
This description provides an overview of the estimated number of neutron stars in the universe. Neutron stars are incredibly dense objects, with a mass of around 1.4 times that of the sun, and a radius of around 10 km. They are formed when a massive star runs out of fuel
A neutron star is the gravitationally collapsed core of a massive supergiant star. It results from the supernova explosion of a massive star—combined with gravitational collapse—that compresses the core past white dwarf star density to that of atomic nuclei. Surpassed only by black holes, neutron stars are the second-smallest- and second-densest-known class of stellar objects. Neutron stars have a radius on the order of 10 kilometers and a mass of about 1.4 solar masses (M☉). Stars that collapse into neutron stars typically have an initial total mass between 10 and 25 M☉ or possibly more for those that are especially rich in elements heavier than hydrogen and helium.