The Life Cycle of Stars
What is a star and how are they classified?
Stars do not have a solid surface, being 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°C to 300 000°C. The core of a star is approximately 15 million degrees Celsius. Stars can range from thousands to millions of kilometres across. Stars appear to twinkle; this is due to the atmosphere moving around us.
There are many things that apply to the classification of stars; brightness, size, colour and temperature. The colour of a star is related to its temperature.
Red - approx. 3000°C
Yellow - approx. 5500°C
White - approx. 10 000°C
Blue - approx. 30 000°C
Stars are classed into different groups due to their size. The biggest and hottest stars are called Supergiants. Big stars are called giants. Our sun is an average sized star and is classed as a Main Sequence star. White dwarfs are the smallest and least bright of all the stars.
range from 30 000°C to 300 000°C. The core of a star is approximately 15 million degrees Celsius. Stars can range from thousands to millions of kilometres across. Stars appear to twinkle; this is due to the atmosphere moving around us.
There are many things that apply to the classification of stars; brightness, size, colour and temperature. The colour of a star is related to its temperature.
Red - approx. 3000°C
Yellow - approx. 5500°C
White - approx. 10 000°C
Blue - approx. 30 000°C
Stars are classed into different groups due to their size. The biggest and hottest stars are called Supergiants. Big stars are called giants. Our sun is an average sized star and is classed as a Main Sequence star. White dwarfs are the smallest and least bright of all the stars.
Life Cycle of Stars
There are two paths that a star can follow through its ‘life’. They are shown in the diagram below:
Stellular Nebula
A stellular nebular is basically a cloud of gas and dust. It is made up primarily of silicon atoms as well as hydrogen and helium. There are two types of stellular nebular. 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 the supernovas of exploding stars. Supernovas are cooling and will eventually form a new average or massive star.
A stellular nebular is basically a cloud of gas and dust. It is made up primarily of silicon atoms as well as hydrogen and helium. There are two types of stellular nebular. 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 the supernovas of exploding stars. Supernovas are cooling and will eventually form a new average or massive star.
Protostar (average star and massive star)
Protostars are composed of hydrogen and helium gases and dust. Their size can range from 5 000 to 8 000 kilometres in diameter. Protostars are not as bright as other stars and appear cloudy or dusty. Eventually protostars will turn into a normal star such as a red giant or red supergiant. Hydrogen to helium fusion will only begin when the temperature reaches 10 million degrees Celsius.
Protostars are composed of hydrogen and helium gases and dust. Their size can range from 5 000 to 8 000 kilometres in diameter. Protostars are not as bright as other stars and appear cloudy or dusty. Eventually protostars will turn into a normal star such as a red giant or red supergiant. Hydrogen to helium fusion will only begin when the temperature reaches 10 million degrees Celsius.
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 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 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 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 our Sun. Red supergiants convert hydrogen into helium which creates large amounts 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 cause the star to collapse and explode outwards in a supernova.
The radius of a red supergiant is 200 to 800 times larger than the radius of our Sun. Red supergiants convert hydrogen into helium which creates large amounts 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 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
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.
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.
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 as our sun. Any matter, such as light and planets, must pass extremely close to a black hole in order to get pulled in. Black holes are usually small in size. A black hole with the same mass as our sun usually has a 3 kilometre radius. Some galaxies, even our own Milky Way galaxy, may have an extremely large black hole at the centre. Black holes cannot be directly observed as they are small, distant and dark.
Black holes are virtually invisible as no light can escape them. When they were first hypothesised they were called “invisible stars”. Black holes can be found by observing its effect of 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 be found by observing its effect of 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.
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 For This Page
EnchantedLearning.com 2010,‘Star Types’, viewed 28 August 2012, <http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml>
Seagrave, W 2012, ‘Red Giant’,viewed 3 September 2012,
<http://historyoftheuniverse.com/index.php?p=redgiant.htm>
Schidtke, K 2012, Stars, teacher notes, Mercy College, Mackay, 2 August.
Steinberg, D, N.A. ‘No Escape: The Truth About Black Holes’, viewed 29 August 2012,
<http://amazing-space.stsci.edu/resources/explorations/blackholes/teacher/sciencebackground.html>
N.A. 2006, ‘Nebulae and Stellar Birth’, viewed 29 August 2012,
<http://burro.astr.cwru.edu/stu/stars_birth.html>
N.A. 2012, ‘Exploding Stars’, viewed 29 August 2012, <http://www.windows2universe.org/the_universe/supernova.html>
Oppenheimer B, Kneebone P 2001, ‘Frequently Asked Questions Regarding Galactic Halo Dark Matter’, viewed 28 August
2012, <http://research.amnh.org/~bro/WD/faq.html>
N.A. N.A. ‘Neutron Stars and Black Holes’, viewed 28 August 2012, <https://www.courses.psu.edu/astro/astro010_pjm25/neutronblack10.html>
N.A. 2012, ‘Black Holes’, viewed 28 August 2012,
<http://science.nationalgeographic.com/science/space/universe/black-holes-article/>
Seagrave, W 2012, ‘Red Giant’,viewed 3 September 2012,
<http://historyoftheuniverse.com/index.php?p=redgiant.htm>
Schidtke, K 2012, Stars, teacher notes, Mercy College, Mackay, 2 August.
Steinberg, D, N.A. ‘No Escape: The Truth About Black Holes’, viewed 29 August 2012,
<http://amazing-space.stsci.edu/resources/explorations/blackholes/teacher/sciencebackground.html>
N.A. 2006, ‘Nebulae and Stellar Birth’, viewed 29 August 2012,
<http://burro.astr.cwru.edu/stu/stars_birth.html>
N.A. 2012, ‘Exploding Stars’, viewed 29 August 2012, <http://www.windows2universe.org/the_universe/supernova.html>
Oppenheimer B, Kneebone P 2001, ‘Frequently Asked Questions Regarding Galactic Halo Dark Matter’, viewed 28 August
2012, <http://research.amnh.org/~bro/WD/faq.html>
N.A. N.A. ‘Neutron Stars and Black Holes’, viewed 28 August 2012, <https://www.courses.psu.edu/astro/astro010_pjm25/neutronblack10.html>
N.A. 2012, ‘Black Holes’, viewed 28 August 2012,
<http://science.nationalgeographic.com/science/space/universe/black-holes-article/>