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24 Space

Great globes of intensely hot gas called stars pour light

and heat into space. A star is born in a vast. NEBULA

of gas and dust and may shine steadily for billions of

years. All the stars except the Sun lie so far away that

their light takes years to reach us.

HOW DO STARS PRODUCE THEIR ENERGY?

Energy is produced in a star’s centre, or core, where

pressures are enormous and temperatures reach

15 million °C (27 million °F). This causes nuclear

fusion – the nuclei of hydrogen atoms collide and fuse

(join) together to form helium. These reactions release

vast amounts of energy, which makes the star shine.

ARE ALL THE STARS THE SAME?

Stars can be very different from each other – in colour,

brightness, temperature, size, and mass. For example,

hot blue-white stars can reach 30,000°C (54,000°F) at

their surface, 10 times hotter than the coolest stars. A

supergiant star can be a billion km (600 million miles)

across, but a neutron star is only the size of a city.

A nebula is a huge cloud of gas and dust found in the space

between the stars. Some nebulas glow. Others are dark – we can

see them only when they are silhouetted against stars or bright

clouds. New stars are born inside dark nebulas.

DO OTHER STARS HAVE PLANETS AROUND THEM?

Since 1995, astronomers have found many planets

circling other stars. These extrasolar planets are mostly

too faint to see but we can detect them by the effects

they have on the motion or brightness of their star.

HOW DO NEBULAS GLOW?

Many nebulas shine. Some shine by reflecting the

light from nearby stars. Others create their own light –

their gas particles glow when they are energized

(given energy) by radiation from nearby stars.

WHAT ARE NEBULAS MADE OF?

Nebulas contain all the ingredients needed to form

stars and planets, including atoms of hydrogen,

oxygen, and nitrogen, and graphite, a form of carbon.

They also contain water and many other molecules.

2 SUPERNOVA 1987A

In 1987, astronomers witnessed

the brightest supernova (star

explosion) of the century. It was

the death of a blue supergiant

star in a nearby galaxy. This

picture is a computer simulation

of what happened to the core

about three minutes after it

collapsed. Matter is rippling

through the core’s outer shell

(pale orange), creating violent

turbulence.

THE CAT’S-EYE NEBULA 3

This mass of glowing gas is a

planetary nebula. It is made up of

layers of gas given off by the star

at the centre, which is dying. The

star is tiny and very hot, and is

known as a white dwarf. A typical

white dwarf has the mass of the

Sun squeezed into a body the

size of Earth, and a temperature

of over 10,000°C (18,000°F).

4 STAR CLUSTER

In the constellation Hercules

is this cluster of hundreds of

thousands of stars packed close

together. Known as M13, it is a

globular cluster. Globular clusters

are found orbiting the centre of

our galaxy. Looser, open clusters

of hundreds of stars are found in

the galaxy’s spiral arms.

NEBULAS

STARS

Stars

Exploding star

originally had a

mass 20 times the

mass of the Sun

Collapsing iron

core sends out

massive shockwaves

Outer layers

of the star are

blasted out

into space