Story of a star’s lifetime told to Honiton U3A members.
PUBLISHED: 16:00 12 May 2015
Dr. Peter Williams was the guest speaker for the April meeting.
The April speaker for the Honiton Univesity of the Third Age’s meeting was Dr. Peter Williams whose talk was entitled Stars and the Universe – Birth, Life and Death of a Star.
He began by illustrating to his audience what can be found in the universe other than stars. This includes planets, asteroids, comets, gas and dust.
It is from the latter two that stars are formed, writes Val Frood.
With the aid of diagrams and excellent photographs taken from telescopes around the world using conventional and infrared cameras, he described how a star begins it’s ‘life’ as just a cloud of gas composed mainly of hydrogen and small amounts of helium and dust. By its own gravity it compresses becoming hotter until at its centre it becomes hot enough (ten million degrees C) to start nuclear reactions which turns the hydrogen to helium.
This creates vast amounts of energy and as a result it shines and so a star is ‘born’.
He then went on to explain that the ‘life’ of a star depends entirely on its mass or weight.
The heavier the star the shorter its life as the nuclear reactions run faster in greater mass stars thus the nuclear fuel is used more rapidly resulting in the supply of hydrogen becoming exhausted.
How a star dies, again depends on its mass. Stars can ‘die’ in three different ways – a small star, having run out of fuel, expands to become a Red Giant then shrinks to become a white dwarf and eventually fades away completely.
Larger stars collapse in on themselves and the force of this huge pressure forces the star to explode as a Supernova.
Finally, if there is enough mass and the Supernova is powerful enough, the core can be compressed to the point that normal space can no longer support it and it compresses to a dimensionless point in space – a black hole!
Dr Williams concluded by emphasising that the time scales used in his talk were, of course, enormous – billions of years. So it was reassuring to learn from him that our own star – the sun, still has an expected life of at least another five billion years.
June Brown thanked Dr Williams on behalf of the Honiton U3A for his very interesting and informative talk.