Transcript Stars
1 of 26 © Boardworks Ltd 2009 2 of 26 © Boardworks Ltd 2009 The Universe The Universe consists of all the matter and the energy that exists. It is believed to be around 14 billion years old, and at least 93 billion light years across. The Universe is believed to have originated in the Big Bang. It is changing all the time, both expanding in size, and changing in composition. It contains billions of galaxies, each containing billions of stars. Even the darkest region of space reveals countless galaxies. 3 of 26 © Boardworks Ltd 2009 Our galaxy – the Milky Way Our solar system lies in the Orion arm of the spiral galaxy called the Milky Way. In the night sky, all of the bright stars and most of the dim ones lie close to us in the same arm of the spiral. There are billions of stars in the Milky Way, with potentially billions of planets in orbit around them. 4 of 26 A computer generated image of the Milky Way. © Boardworks Ltd 2009 How is a star formed? 5 of 26 © Boardworks Ltd 2009 How is a planet formed? 6 of 26 © Boardworks Ltd 2009 The formation of the solar system 7 of 26 © Boardworks Ltd 2009 8 of 26 © Boardworks Ltd 2009 Pressure and temperature The gas in an aerosol is at room temperature and at a high pressure. When released, the gas is at a much lower pressure, and feels relatively cold. When pressure decreases, temperature decreases. Why does it feel colder when you climb a mountain? The upper atmosphere has lower air pressure. 9 of 26 © Boardworks Ltd 2009 Protostar pressure 10 of 26 © Boardworks Ltd 2009 Finding stability When the temperature in the core of a protostar reaches roughly 14 million Kelvin, nuclear fusion begins and a stable star is born. The star now enters its stable phase. A star is stable when its size remains constant over time. All stars have a stable period in their lives, the length of which is determined by their mass. The Sun is halfway though its nine billion year stable phase. 11 of 26 © Boardworks Ltd 2009 What makes a star stable? Inside a star, the energy released by fusion produces an outward acting force. This causes star expansion. explosive force of fusion However, the star’s huge mass means that gravity is acting in the opposite direction, forcing particles towards the core. gravitational force 332,948 Earth masses If these two forces are equal, then the star will not change its size. It is said to be stable. 12 of 26 © Boardworks Ltd 2009 Stable star structure 13 of 26 © Boardworks Ltd 2009 14 of 26 © Boardworks Ltd 2009 The death of a star 15 of 26 © Boardworks Ltd 2009 The end of stability A star’s stable phase ends when most of its hydrogen has been consumed by fusion. The reduction in fusion causes the core to cool. This lowers the pressure causing the star to collapse upon itself under its own gravity. As the outer layers contract, they heat up. This triggers the fusion of the remaining hydrogen. The increased energy output in the outer layers causes them to expand. The star increases massively in size, becoming a red giant. 16 of 26 © Boardworks Ltd 2009 What happens in the core? The core continues to contract. This causes it to reach new extremes of temperature (over 100 million Kelvin) and pressure. This gives helium atoms enough energy to fuse. Thus heavier atoms, such as carbon and oxygen, are produced. In the largest stars elements as heavy as iron can be produced. However such large stars will suffer a different fate to the Sun. 17 of 26 © Boardworks Ltd 2009 Red supergiants 18 of 26 © Boardworks Ltd 2009 Making large atoms Hydrogen is the simplest element, containing a single proton in its nucleus, and a lone orbiting electron. When deuterium and tritium atoms, both hydrogen isotopes, fuse together inside a star, helium is produced. Heavier elements are produced when a star becomes a red giant. Only a supernova can produce elements heavier than iron, such as silver, gold and uranium. tritium deuterium 19 of 26 helium carbon © Boardworks Ltd 2009 Making large atoms 20 of 26 © Boardworks Ltd 2009 In the beginning… The Universe is widely believed to have started with the Big Bang. This colossal explosion brought all matter into existence, in the form of subatomic particles. It was not until the first stars formed that any matter more complex than hydrogen existed. As these early stars progressed through their life cycles, they introduced increasingly complex elements into the Universe. 21 of 26 © Boardworks Ltd 2009 The changing universe 22 of 26 © Boardworks Ltd 2009 23 of 26 © Boardworks Ltd 2009 Glossary 24 of 26 © Boardworks Ltd 2009 Anagrams 25 of 26 © Boardworks Ltd 2009 Multiple-choice quiz 26 of 26 © Boardworks Ltd 2009