Unit 5 - Astrophysics - Classification of Stars Flashcards
Define ‘Apparant Magnitude’.
The brightness of a star as seen from Earth.
Define ‘Absolute Magnitude’.
The brightness of star if it were at a distance of 10 parsecs from the observer
How do you determine the ratio of brightnesses between adjacent star classes.
What is the relationship between apparent and absolute magnitude?
Describe for Class O star:
Temperature.
Colour.
Prominent absorbtion lines.
25,000-50,000K
Blue
ionised and neutral Helium and weak hydrogen
Describe for Class B star:
Temperature.
Colour.
Prominent absorbtion lines.
11,000-25,000K
Blue/White
Neutral helium and moderate hydrogen.
Describe for Class A star:
Temperature.
Colour.
Prominent absorbtion lines.
7,500 - 11,000K
White with blue tinge
Strong hydrogen and ionised metals
Describe for Class F star:
Temperature.
Colour.
Prominent absorbtion lines.
6,000-7,500K
White
Ionised metal and weak hydrogen
Describe for Class G star:
Temperature.
Colour.
Prominent absorbtion lines.
5,000K-6,000K
Yellow/White
Neutral and ionsied metal, weak hydrogen
Describe for Class K star:
Temperature.
Colour.
Prominent absorbtion lines.
3,500-5,000K
Orange
Neutral metals
Describe for Class M star:
Temperature.
Colour.
Prominent absorbtion lines.
2,000-3,500
Red
molecules/neutral metals/Titanium oxide
What class of star is the sun in?
Class G
Define a black body.
A black body is a body that completely absorbs all wavelengths of electromagnetic radiation that fall upon it and reflects and transmits none.
Draw a black body curve for three different temperatures: P,Q,R where P>Q>R
What is Wien’s Displacement Law
That the product of the maximum wavelength and the temperature is constant.
What is Stefan’s Law?
The energy emitted per second by a black body is given by:
Draw a Hertzsprung - Russel diagram.
What is the lifecycle of a star with similar mass to the Sun
When the hydrogen runs out, the star collapses causing rapid temperature rise and helium fusion begins which causes the star to expand to a huge size whilst cooling - a red giant.
When the star is mainly carbon it collapses again to form a white dwarf.
What is the Chandrasekhar limit?
The maxiumum possible mass that a white dwarf can have without collapsing under its own weight to become a neutron star or black hole.
Define a neutron star.
The left over remains from a supernova
What is a black hole?
A concentration of matter which has a gravitational field strong enough to curve space-time around itself so not even light can escape.
A place where the escape velocity is greater than the speed of light.
What is the Schwarzchild radius?
The distance from the centre of a black hole where the escape velocity is equal to the speed of light.
Define the event horizon.
An imaginary surface around a black hole where the escape velocity is equal to the speed of light.
How will the Sun change when it evolves into a red giant?
(Three marks)
When hydrogen in the core runs out gravitational forces overwhelm radiation pressure and the star initially collapses.
This collapse causes a rapid rise in core temperature and helium fusion begins.
The gas/radiation pressure now overwhelm gravity and the star expands to a huge size cooling as it does so.
Explain how a white dwarf is formed and describe what a white dwarf is.
Once fusion stops gravity overwhelms gas pressure and the star collapses to a very small, very dense and very hot white dwarf made mainly of carbon.
No more fusion takes place and the star gradually cools.
In what conditions is a black hole formed?
If a neutron star left after a supernova is greater than three times the mass of the Sun then it will continue to collapse under gravity to a singularity and form a black hole.
