Stars – Birth and Death
Mullard Radio Astronomy Observatory
Stars – Birth and Death
Throughout our Galaxy, new generations of stars are continually being born and old generations are dying. Radio telescopes allow us to observe the very earliest and latest stages of a star’s life: these observations help us understand how the Sun, Earth and planets formed, and how they will die.
Violent processes accompany both the birth and death of stars. During the formation phase, in which a cold cloud of molecular gas collapses due to gravity, fast jets of gas can often be seen being ejected from the forming star at the centre of the cloud. In the picture on the right there are faint twin jets of molecular gas moving away from the young star; on the scale of this picture this star, marked by the white cross, is no larger than a pinhead. These narrow jets move away from the star at about 100 kilometres per second; further out, they interact with the surrounding cloud and expand to produce the two bright lobes of emission seen in the picture. Over the next million years or so, this activity will die down and the young star producing these jets will come to resemble our own Sun, and may even have planets of its own.
The picture above was made using the James Clerk Maxwell Telescope (shown left), an instrument with which the staff of the Observatory have a very close link. It is a radio telescope with a very precise surface, allowing it to operate at wavelengths of about 1 mm. At these wavelengths, the earth’s atmosphere is not particularly transparent and it is necessary to observe from high altitudes: this telescope is located at 4200 m on Mauna Kea, in Hawaii.
Supernovae
At the ends of their lives, many stars undergo a violent death: when the supply of nuclear fuel runs out in a massive star, the whole star can explode in a few seconds in an event called a supernova. The optical light from the star brightens for a month or so; but at radio wavelengths we can observe the aftermath of the explosion for up to ten thousand years. The material is ejected at up to 10,000 kilometres per second and produces strong radio waves as it expands into the space around the star. The image on the right is a Ryle Telescope radio map of just such a supernova which exploded 300 years ago. At the centre of a supernova, the remains of the star can collapse to form a compact, dense object called a neutron star which spins rapidly on its axis and emits pulses of radio waves as it spins. Such pulsars were first discovered by Jocelyn Bell and Tony Hewish at the Observatory, in 1967.
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