Life Cycle of Stars Revision Questions

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  • Created by: Lizzy Day
  • Created on: 26-06-16 19:50
What are spectral classes?
Stars are classified into groups called spectral classes. The spectral class of a star depends on the relative strength of certain absorption lines. There are seven main spectral classes; O, B, A, F, G, K and M.
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What are the properties of the spectral class 'O'?
colour- blue, temperature - 25,000 -50,000K, absorption lines - the strongest are He+ and He absorptions, since these need a really high temp. They have weak H lines too.
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What are the properties of the spectral class 'B'?
colour-blue, temperature- 11,000 - 25000K, absorption lines - these spectra show strong Helium atom and hydrogen absorptions
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What are the properties of the spectral class 'A'?
colour- blue/white, temperature - 7,500 - 11,000K, absorption lines- visible spectra are governed by very strong Hydrogen Balmer lines, but there are also some metal ion absorptions.
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What are the properties of the spectral class 'F'?
colour - white, temperature- 6,000-7,500K, absorption lines - these spectra have strong metal ion absorptions
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What are the properties of the spectral class 'G'?
colour- yellow/white, temperature - 5,000-6,000K, absorption lines - both metal ion and metal atom absorptions
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What are the properties of the spectral class 'K'?
colour - orange, temperatre - 3,500-5,000K, absorption lines - mostly from neutral metal atoms
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What are the properties of the spectral class 'M'?
colour - red, temperature -
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What does the Hertzsprung-Russel diagram show?
The diagram is really important for studying how stars evolve. A graph of absolute magnitude vs temperature/spectral class for stars became known as this.
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What does the diagonal band show in the diagram?
The long, diagonal band is called the main sequence. Main sequence stars are in their long-lived stable phase where they are fusing hydrogen into helium. The sun is a main sequence star.
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What does the top right area show in the dragram?
Stars that have a high luminosity and a relatively low temperature must have a huge surface area because of Stefan's law. These stars are called red giants
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What does the bottom left area show in the diagram?
Stars that have low luminosity but a high temperature must be small (Stefan's law). These stars are called white dwars.
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How do stars first form?
All stars are born in a cloud of dust and gas, most of which was left when previous stars blew themselves apart in supernovae. The dense clumps of the cloud contract under the force of gravity.
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What are protostars?
When the dense clumps get dense enough, the cloud fragments into regions called protostars, that continue to contract and heat up.
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How does a star become a main sequence star?
Eventually, the temp at the centre of the protostar reaches a few million degrees, and hydrogen nuclei start to fuse together to from helium. This releases an enormous amount of energy and creates enough pressure to stop the gravitational collapse
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What is core hydrogen burning?
Stars spend most of their lives as main sequence stars. The pressure produced from hydrogen fusion in their core balances the gravitational force trying to compress them.
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How does a star become a red giant?
When the hydrogen in the core runs out, nuclear fusion stops, and with it the outward pressure stops. The core contracts and heats up under the weight of the star, the outer layers expand and cool.
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What is shell hydrogen burning?
The material surrounding the core still has plenty of hydrogen. The heat from the contracting core raises the temperature of this material enough for the hydrogen to fuse.
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What is core helium burning?
The core continues to contract, until, eventually, it gets hot enough and dense enough for helium to fuse into carbon and oxygen. This is called core helium burning. This releases a huge amount of energy, which pushes out the outer layers of the star
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What is shell helium burning?
When the helium runs out, the carbon-oxygen core contracts again and heats the shell around it so that helium can fuse in this region.
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What happens to low-mass stars?
The C-O core won't get hot enough for any further fusion and so it continues to contract under its own weight. Once the core has shrunk, electrons exert pressure to stop it collapsing any more.
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How is a planetary nebula formed?
The helium shell becomes more and more unstable as the core contracts. The star pulsates and ejects its outer layers into space as a planetary nebula, leaving behind the dense core.
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How is a white dwarf formed?
The star is a very hot, dense solid called a white dwarf, which will simply cool down and fade away.
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What happens to high-mass stars?
High-mass stars have a shorter life and a more exciting death than a lower-mass star. Even though stars with a large mass have alot of fuel, they use it up more quickly and don't spend as long as main-sequence stars.
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What happens in the red-giant stage?
When high mass stars are red-giants, the 'core burning to shell burning' process can contribute beyond the fusion of He, building up layers in an onion-like structure.
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How is a white dwarf formed?
In high mass stars, when the core of the star runs out of fuel, it starts to contract- forming a white dwarf core. But, if the star is massive enough, electron degeneracy can't stop the core contracting.
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How is a supernova formed?
In high mass stars, if the core continues to contract, the outer layers of the star fall in and rebound off the core, setting up huge shockwaves. These shockwaves cause the star to explode cataclysmically in a supernova
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How is a neutron star formed?
As the core of a massive star contracts, the electrons in the core material et squashes onto the atomic nuclei and combine with protons to form neutrons and neutrinos. The core suddenly collapses to become a neutron star.
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What are some of the properties of neutron stars?
Neutron stars are incredibly dense. They're very small, typically about 20km across, and they can rotate very fast.
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What happens if the core of the star is more than 3 solar masses?
The core will contract until neutrons are formed, but now the gravitational force on the core is greater, the neutrons can't withstand this gravitational force. Nothing stops it completely collapsing.
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How is a black hole formed?
When a massive star collapses into an infinitely dense point, a region around it has such a strong gravitational field that it becomes a black hole - an object whose escape velocity is greater than the speed of light, l. Not even light can escape.
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Card 2

Front

What are the properties of the spectral class 'O'?

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colour- blue, temperature - 25,000 -50,000K, absorption lines - the strongest are He+ and He absorptions, since these need a really high temp. They have weak H lines too.

Card 3

Front

What are the properties of the spectral class 'B'?

Back

Preview of the front of card 3

Card 4

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What are the properties of the spectral class 'A'?

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Card 5

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What are the properties of the spectral class 'F'?

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