Eventually, the massive iron core succumbs to gravity and it collapses to form a neutron star. The outer layers of the star fall in and bounce off the neutron core which creates a shock wave that blows the outer layer outward. This is the supernova explosion. Stars Black holes and neutron stars don't give off light, so we can't just look for them. However, astronomers can find black holes and neutron stars by observing the gravitational effects on other objects nearby.
Astronomers can discover some black holes and neutron stars because they are sources of x-rays.
The intense gravity from a black hole or a neutron star will pull in dust particles from a surrounding cloud of dust or a nearby star. As the particles speed up and heat up, they emit x-rays. So the x-rays don't come directly from the black hole or neutron star, but from its effect on the dust around it. Rotating stars Many stars rotate around each other, much as the planets orbit our Sun. When astronomers see a star circling around something, but they cannot see what that something is, they suspect a black hole or a neutron star.