This is the life cycle of stars:
What is a star and how are they classified?
Stars do not have a solid surface as they are a sphere of hot glowing gas. The brightness of stars comes from the fusion reactions that occur at the core. Hydrogen fusing into helium produces energy through light. The temperature on the surface of a star can range from 30 000 degrees to 300 000 degrees. The core of a star is approximately 15 million degrees Celsius. Stars can range form thousands to millions of kilometres across. Stars appear to twinkle, this is due to the atmosphere moving around us.
There are many things that are involved in the classification of stars including; brightness, size, colour and temperature. The colour of a star is related to its temperature.
Red -Approx 3000 degrees Celsius
Yellow -Approx 5500 degrees Celsius
White -Approx 10 000 degrees Celsius
Blue -Approx 30 000 degrees Celsius
Stars are classified into groups due to there size. The biggest and hottest stars are called super-giants. Big stars are called giants. Our sun in an average size and is classed as a main sequence star. White dwarfs are the smallest and least bright of all stars.
There are many things that are involved in the classification of stars including; brightness, size, colour and temperature. The colour of a star is related to its temperature.
Red -Approx 3000 degrees Celsius
Yellow -Approx 5500 degrees Celsius
White -Approx 10 000 degrees Celsius
Blue -Approx 30 000 degrees Celsius
Stars are classified into groups due to there size. The biggest and hottest stars are called super-giants. Big stars are called giants. Our sun in an average size and is classed as a main sequence star. White dwarfs are the smallest and least bright of all stars.
Life Cycle of Stars
There are two paths that a star can follow in its life. They are shown in the diagram below:
Stellar Nebula
A Stellar Nebular is basically a cloud of gas and dust. It is primarily made up of silicone atoms as well as hydrogen and helium. There are two types of Stellar Nebula. The first is made up of material from the beginning of the universe. Soon after the birth of the universe atoms were created and they formed into clouds. The second type is made by supernovas of exploding stars. Supernovas are cooling and will eventually for an average or massive star.
Protostar (average star massive star)
Protostars are composed of hydrogen and helium gases and dust. The size can range from 5 000 to 8 000 kilometres in diameter. Protostars do not appear to be as bright as other stars. They also appear to be cloudy or dusty. Eventually protostars will turn into a normal star such as a red giant or a red supergiant. Hydrogen to helium fusion will only begin when the temperature reaches 10 million degrees
Red Giant
Red giants convert hydrogen into helium. This creates energy which is released as light. After billions of years the centre of the red giant will run out of protons for fusing hydrogen into helium. As it runs out of fuel it will begin to cool and contract. The outer layers of the star fall inwards due to gravity and will begin to heat up. The layer around the core becomes hot enough to fuse protons into helium. This outer layer is then called the helium fusion shell. Now that the star has gained a new source of energy it is hotter than it was in its normal life. This heat causes the outer layers of the star to swell.
Red supergiant
The radius of a red supergiant is 200 to 800 times larger than the radius of the sun. Red supergiants convert hydrogen into helium which creates a huge amount of energy. This energy is released as energy and makes them very bright. It is composed of a large amount of carbon. The outside is cooler at approximately 3500K. Eventually a supergiants energy for fusion reactions will run out. There will be no force resisting the inward push of gravity which will eventually cause the star to collapse and explode outwards in a supernova.
Supernova
During the short interval of a supernova explosion more light is emitted than a sun does in a lifetime. This light is brighter than a galaxy of 100 billion stars. Many elements that are found in our bodies were forged in a supernova. If a star was only a few times bigger than our sun its core would shrink down to a tiny neutron star after exploding in a supernova. If a star was many times bigger than our sun its core would shrink down to a black hole
White Dwarf
Dwarfs stars are in the last stage of a stars lifecycle. Approximately 94% of stars end their life as a white dwarf. White dwarfs are usually around the same size as our earth. At first they are very hot and have large amounts of energy. As this energy builds up the white dwarf cools down and becomes a black dwarf. White dwarfs are made up of waste products of the nuclear fusions. These waste products are mostly carbon and oxygen.
Neutron Star
Neutron stars are approximately 20 kilometres in diameter and 1.4 times our Suns mass. After they have finished burning their fuel they undergo a supernova explosion. Neutron stars consist of tightly packed neutrons, hence the name ‘neutron’ star.
Black Holes
Black holes are the cold remains of former stars. They are so dense that no matter, not even light, can escape its gravitational pull. Black holes are the last evolutionary stage of stars that were 10 to 15 times the size of our sun. A black hole with the same mass as our sun would have the same gravitational pull. Any matter such as planets and light would have to pass extremely close to the black hole in order to get sucked in.Black holes are usually small in size. A black hole that is the same size as our sun usually has a three kilometre radius. Some galaxies, even our milky way galaxy, may have an extremely large black hole in the centre. Black holes can not be directly observed as they are to small, dark and distant.
Black holes are virtually invisible as no light can escape them.when they were first hypothesised they were called "invisible stars". Black holes can can be found by observing its effect on the stars and gasses around it. We can infer the presence of a black hole due to the heat and motion of the circulating matter.
Black holes are virtually invisible as no light can escape them.when they were first hypothesised they were called "invisible stars". Black holes can can be found by observing its effect on the stars and gasses around it. We can infer the presence of a black hole due to the heat and motion of the circulating matter.
Hertz-Sprung Russel diagram
A Hertz-sprung Russel diagram allows us to plot temperature, luminosity and temperature of stars. The general relationship between the temperature and star brightness is the hotter the star is the brighter it is. This relationship is more likely seen in main sequence stars than red giants or white dwarfs. Another relationship that can be seen in a Hertz-sprung Russel diagram is between colour
and temperature, again this relationship is seen more often in main sequence stars. The coldest stars are red in colour and the hottest are blue. Our sun is a main sequence star and is relatively low on the diagram, having a temperature of 5,300°C (therefor being yellow) and having a brightness of 1. A star classified as class B is blue in colour and has a temperature that is higher than 7,500°C.
Below is an example of a Hertz-sprung Russel diagram.
and temperature, again this relationship is seen more often in main sequence stars. The coldest stars are red in colour and the hottest are blue. Our sun is a main sequence star and is relatively low on the diagram, having a temperature of 5,300°C (therefor being yellow) and having a brightness of 1. A star classified as class B is blue in colour and has a temperature that is higher than 7,500°C.
Below is an example of a Hertz-sprung Russel diagram.
Bibliography:
EnchantedLearning.com 2010,'Life Cycle of Stars', Viewed 2 November 2012 http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/
Musium victoria n.d,'Black Holes journey into the unknown', viewed 21 November 2012, http://museumvictoria.com.au/planetarium/whatson/black-holes/
N.A 2009,'Life Cycle of a Star', Viewed 2 November 2012 http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Lifecycle_of_a_Star.html
NASA N.A,'The Stellar Nebular-Where a star is born', Viewed 7 November 2012
http://people.duke.edu/~teb/stars/nebula.html
National Geographic Society 1996,'Neutron Stars', viewed 18 November 2012 http://science.nationalgeographic.com.au/science/space/solar-system/neutron-stars/
National Geographic Society 1996,'White Dwarfs', viewed 18 November 2012
http://science.nationalgeograpic.com/science/space/universe/white-dwarfs-article/html
History of the universe 2006,'Red Giant', viewed 14 November 2012 http://www.historyoftheuniverse.com/starold.html
Science daily 1995,'Red supergiant star', viewed 14 November 2012
http://www.sciencedaily.com/articles/r/red_supergiant.htm
Musium victoria n.d,'Black Holes journey into the unknown', viewed 21 November 2012, http://museumvictoria.com.au/planetarium/whatson/black-holes/
N.A 2009,'Life Cycle of a Star', Viewed 2 November 2012 http://www.nasa.gov/audience/foreducators/topnav/materials/listbytype/Lifecycle_of_a_Star.html
NASA N.A,'The Stellar Nebular-Where a star is born', Viewed 7 November 2012
http://people.duke.edu/~teb/stars/nebula.html
National Geographic Society 1996,'Neutron Stars', viewed 18 November 2012 http://science.nationalgeographic.com.au/science/space/solar-system/neutron-stars/
National Geographic Society 1996,'White Dwarfs', viewed 18 November 2012
http://science.nationalgeograpic.com/science/space/universe/white-dwarfs-article/html
History of the universe 2006,'Red Giant', viewed 14 November 2012 http://www.historyoftheuniverse.com/starold.html
Science daily 1995,'Red supergiant star', viewed 14 November 2012
http://www.sciencedaily.com/articles/r/red_supergiant.htm