The gravitational collapse of huge clouds of gas and dust that are found mainly in the spiral arms of galaxies, forming protostars.
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What is an example of an emission nebula and what causes this nebula to glow?
The Orion Nebula, which emits light by fluorescence when the glowing gas contained in the nebula is excited by newly-formed stars.
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How do protostars become main sequence stars?
They rise in temperature and eventually reach 15 million K, a temperature high enough for the nuclear fusion of hydrogen nuclei to helium. The outward pressure from the radiation generated in the star's core halts any further collapse of the star.
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How long are main sequence phases for large-mass and low-mass stars?
100 million years for large-mass stars and 1 million million years for low-mass stars.
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What is the Sun's estimated main sequence lifetime and how far through is it?
The Sun is about halfway through it's 10,000 million year main sequence lifetime.
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How are red giants and supergiants formed?
When the hydrogen which fuels a star's core runs out, the outward radiation pressure disappears and the star collapses under gravity. The star's temperature rises and further nuclear reactions occur, causing the star to expand and cool.
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How is a planetary nebula formed?
With further hydrogen depletion and contraction, the temperature at the centre of a red giant can rise to as hot as 100 million K; this is hot enough for helium nuclei to fuse to form carbon. This causes the red giant to lose its outer layers.
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What are the properties of a white dwarf and how do they form?
White dwarfs form when the inner part of the red giant (left behind in the formation of the planetary nebula) collapses. They are highly dense and eventually cool to form red, brown and eventually black dwarfs.
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What is a supernova?
A violent explosion occurring at the outer part of a supergiant's core, blowing away its outer layers at speeds of up to 5000km/s.
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What is a supernova remnant?
The remaining dense core left after a supernova, which can be either a neutron star or black hole.
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What are neutron stars?
Highly dense (a mass greater than the Sun's contained in a sphere 20km wide) that cause such strong gravitational effects that they are able to rotate very rapidly on their axes.
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What are pulsars?
Regular, short 'pulses' of intense radio waves emitted by rotating neutron stars.
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Why is electromagnetic radiation unable to escape a black hole?
Because a black hole is highly dense and has a strong gravitational pull.
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How can black holes be detected?
X-rays emitted by gas molecules entering the black hole.
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How was sunlight first split into its component colours and by who?
Isaac Newton using a glass prism.
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What equipment is used by modern astronomers to split sunlight into its component colours?
Diffraction grating.
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Describe a stellar spectrum.
A series of dark spectral lines (caused by atoms, ions and molecules in the outer regions of the star absorbing particular light wavelengths) superimposed on a continuous coloured background.
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What can be deduced from a stellar spectrum?
The star's chemical composition (each chemical element has its won unique set of spectral line wavelengths), temperature (which in turn determines its colour) and possible radial velocity (using the Doppler Effect).
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What is a star's spectral type dependent upon?
The relative numbers and wavelengths of its spectral lines.
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How are spectral types classified in the Harvard scheme?
Using the letters O, B, A, F, G, K and M, followed by a number from 0 to 9. O-type stars are the hottest while M-type stars are the coolest.
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What information is most commonly plotted on a Hertzsprung-Russell (H-R) diagram?
The star's luminosity (the amount of energy emitted by the star in a given time) against spectral type/'surface' temperature.
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Other cards in this set
Card 2
Front
What is an example of an emission nebula and what causes this nebula to glow?
Back
The Orion Nebula, which emits light by fluorescence when the glowing gas contained in the nebula is excited by newly-formed stars.
Card 3
Front
How do protostars become main sequence stars?
Back
Card 4
Front
How long are main sequence phases for large-mass and low-mass stars?
Back
Card 5
Front
What is the Sun's estimated main sequence lifetime and how far through is it?
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