NEUTRON STARS AND PULSARS
HOW THEY FORM
HOW WE DETECT THEM
Q & A PAGES
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.
X-raysAstronomers 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. Although x-rays don't penetrate our atmosphere, astronomers use satellites to observe x-ray sources in the sky.
Rotating starsMany 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.
Gravity lensesAstronomers use a technique called gravity lensing to search for black holes and neutron stars. When a very massive object passes between a star and the earth, the object acts like a lens and focuses light rays from the star on the Earth. This causes the star to brighten.
How can a black hole or a neutron star act like a lens? The answer comes from Albert Einstein, who proved in 1919 that light follows in the path of the bent time and space which is warped due to the gravitational force of a massive object. Einstein predicted that a star positioned behind the sun would be visible during a total eclipse. The Sun bent the light rays coming from the star and made it appear next to the sun.