The Birth of Stars

Astronomers have pieced together the story of how stars form by observing the many different stars that can be seen from Earth. Stars change throughout their life and eventually die.

A star’s birthplace

New stars form within vas clouds of gas and dust, called nebulae. Some nebulae are bright and some are dark. Dark nebulae are made mostly of dust and so they blot out the light of stars behind them. They look like dark patches of starless sky.

 Most nebulae can only be seen through a telescope, but you can see the nebula M42, with binoculars. It lies in Orion. There is another nebula dark nebula, called the Horse’s Head Nebula is silhouetted against a bright nebula. The Horse’s Head also lies in the constellation Orion. You need a powerful telescope to see this nebula.

 Another bright Nebula is the Trifid Nebula. The gases in it are so hot that they make the surrounding gas clouds glow in beautiful shades. Hydrogen glows pink, while oxygen glows green-blue. You need a good telescope to see it.

Starting Off

Before stars begin to form in a nebula, the clouds of gases and dust swirl around and around. They then form into clumps which grow larger and larger.

Cloud Collapse

Eventually, something causes the clouds to collapse. Some astronomers think that this might happen when the clouds pass through the arms of a spiral galaxy. Some suggest that the shock waves from an exploding star might start the collapse.

Shining star

 As the cloud collapses, the temperature rises inside. After tens of thousands of years of collapse, a hot core forms. The core gets hotter and hotter until nuclear reactions begin inside, making the clump of gases start to shine. The new star has been born. Most new stars are hot and bright, but some are cooler and dimmer.

Our Sun

At first, most new stars burn very brightly. They appear either blue or white. This state continues for millions of years.

 As they get older, they settle down and shine less brightly but more steadily, like our Sun. The Sun is only halfway through its lifespan of around 10,000 million years.