What is a black hole?
A black hole is an area in space where the force of gravity is so strong that even light cannot escape from it. Black holes are created when a burned-out star collapses. Eventually it shrinks into a tiny sphere of material. The gravity of this material is so powerful that it pulls in everything around it. Even light it is sucked into the black hole. Nothing that goes into a black hole ever comes out. We cannot see black holes. We can sometimes identify them from the radio waves given off as a star is drawn into a black hole.
How far away are stars?
The nearest star to the Earth is our own Sun, which is 152 million km away. After the Sun, the closest stars are Proxima Centauri and Barnard’s Star. The farthest stars in our Galaxy are 80,000 light-years away. Other galaxies, each one containing millions of stars, are much more distant.
Why do stars twinkle?
Most stars burn steadily and if we could see them from space they would not be twinkling at all. As the light from a star passes through the Earth’s atmosphere, it is bent by changes in the air temperature. This makes the light appear to flicker. Because of this effect astronomical observatories are situated on mountain-tops. Higher up, the air is thinner and is less likely to cause this twinkling effect.
Neutron stars
When massive stars explode violently it can lead to a supernova. If the core survives it may become a neutron star. The rapid collapse of the outer part of the star leads to temperatures of over 1,000 million degree Celsius and leaves the core with an average diameter of just 20 km. However, the star still has a mass of up to three times that of our Sun making it incredibly dense. One teaspoonful of neutron star weighs over three billion tonnes!