STAR TYPES

Anyone looking up at the stars at night could be forgiven for thinking that all stars are fairly similar. But although they might all look the same from down here on Earth, they are strikingly varied. Here are just a few of the different types of stars:

· BINARY STARS

Most of the stars you look at in the sky aren't single points of light like our Sun. On closer inspection through a telescope, you can see that they are two or more stars that live very close together.

Unlike our own Sun, most stars are part of binary or multiple stars systems. If our largest planetary neighbour, Jupiter had been a bit larger then it would have exploded into a stellar companion to the Sun.

Explore the planets with our travel guide to the Solar System

· PROTOSTARS

This is a baby star at the earliest observable stage of formation. Although the star is forming from interstellar gas, it is not yet hot enough for nuclear reactions to start in its core.

· DWARFS

Our Sun is a dwarf star. Throughout their lives, stars go through many phases of expansion and contraction. When they are a normal size for their weight they are called 'dwarfs'.

Brown and black dwarfs are thought to contribute to the missing dark matter that lurks invisibly inside the Universe.

Find out more about the dark matter mystery

· SUPERGIANTS

Giant stars have luminosities reaching 1000 times that of the Sun and are up to 200 times as wide. Again, they can be all sorts of colours according to their temperature.

The largest stars are called supergiants. The biggest ever found is 10 million times as bright as the Sun. If it were in the same position as the Sun it would engulf the Earth and stretch even further beyond.

· SUPERNOVAE

When an old massive star has run out of all its fuel, it collapses amidst a catastrophic explosion called a supernova. This releases so much light that it can outshine a whole galaxy of stars put together.

This leaves behind a cloud of brightly coloured gas, called 'nebula'. In some cases, a neutron star is also left behind. The Crab Nebula is the legacy of a supernova spotted by the ancient Chinese astronomers in 1054 AD and harbours a pulsar (a type of neutron star) at its heart.

· NEUTRON STARS

After exploding as a supernova, a star about twice as big as the Sun would form a neutron star.

They have collapsed so much that their atoms have been crushed, squashing the protons and electrons together until they merge to leave only neutrons.

This makes them very dense. If we could transport a teaspoon of material from a neutron star to Earth, it would weigh as much as a mountain. It also makes them spin at amazing speeds. Some can revolve hundreds of times a second.

· PULSARS

Pulsars are a special kind of neutron star that emit radio waves in regular bursts. They do this by spinning like the beam on the top of a lighthouse. But rather then emitting light, they sweep a beam of radio waves across the Universe as they spin.

Some also emit X-rays. A pulsar has a mass similar to the Sun, but a diameter of only around 10km.

· VARIABLE STARS

Some stars also pulsate. They grow and shrinking in size periodically. These include the strange sounding Cepheid variables, RR Lyrea and Mira star types.

Cepheid variables are particularly interesting to astronomers. Because there is a direct link between their brightness and their pulsation cycle, they can calculate how distant these stars are. So Cepheid variables are used as 'cosmic rulers' to measure the distance from us.

· GAMMA RAY BURSTS

Gamma ray bursts were discovered by chance by military satellites monitoring nuclear testing in the late 1960s.

They are intense bursts of gamma and X-ray radiation that only last for a few seconds. But these bursts are millions of times more powerful than the output of an entire galaxy.

· HYPERNOVAE

One possible explanation for the origin of Gamma ray bursts is that they are the result of extremely large explosions, or a 'hypernova'.

Hypernovae are the death throes of stars up to 20 times larger than our own Sun. Such explosions emit, for just a few seconds, more radiation than everything else in the Universe combined.

Yet despite their destructive power, hypernovae may also be responsible for the creation of stellar nurseries, where new stars (or protostars) are born.

· QUASARS

These are amongst the most distant things ever seen in space, living at the heart of energetic 'active' galaxies billions of light years away from us.

But their light is not produced by normal nuclear reactions like stars. A quasar is powered by the central supermassive black hole, which lies at their centre. Friction from matter spiralling into the black hole produces their brilliant glow.

Explore black holes further