14 Stellar Evolution Flashcards
Why is it difficult to classifying stars by their brightness?
The brightness they appear from Earth also depends on their distance from the Earth.
The closer the star, the brighter it appears.
What is the name of the long stable period a star enters when the outward pressure caused by thermal expansion balances the force of gravity pulling everything inward.
The main sequence
Describe the absolute magnitude scale.
-10 0 +10
Stellar evolution for a small mass star is…
Nebula –> Protostar –> Main sequence star –> Red giant –> white dwarf
What evolutionary stages does a large mass star go through?
Large mass star
Nebula –> Protostar –> Main sequence star –> Red super giant –> Supernova –> Neutron star
Stellar evolution for a low mass star is…
Nebula –> Protostar –> Main sequence star –> Red giant –> white dwarf
What evolutionary stages does a very large mass star go through?
Very large mass star
Nebula –> Protostar –> Main sequence star –> Red super giant –> Supernova –> Black hole
Where are the cool and dim stars found on the HR diagram?
Bottom right
Which of the following is not formed after a supernova?
A. a neutron star
B. a black hole
C. a red super giant
C. a red super giant.
On the Hertzsprung-Russell diagram, white dwarfs group together because they have…
A ..negative absolute magnitudes and high temperatures
B .. negative absolute magnitudes and low temperatures
C .. positive absolute magnitudes and high temperature
C .. positive absolute magnitude and high temperatures
White dwarfs are dim and hot!
NOTE: Confusingly, the low absolute magnitude, the brighter the star ( -4 is brighter than +5)
The absolute magnitude of a star is..
A. how bright the star would appear if it was at a standard distance from Earth
B. the brightest the star could appear to an observer
C. how bright the star appears from Earth
A. how bright the stat would appear if it was at a standadrd distance from Earth.
This allows us to compare the brightness of stars without worrying about their relative distances from Earth.
A hot star will emit most its visible light at the _____________ frequencies of visible light.
highest (blue)
Locate the white dwarf in the HR diagram below.
D
white dwarf stars are dim and cool
Eventually a star runs out of hydrogen in it core. The force of gravity inward is larger than the pressure of thermal expansion outward.
The star is compressed, until it is dense and hot enough that the energy (and so the pressure) created makes the outer layers of the star expand.
What is the name of this stage?
red giant (small mass star)
red supergiant (large mass star)
Where are the hot and dim stars found on the HR diagram?
Bottom left
A cool star will emit most its visible light at the _____________ frequencies of visible light.
lowest (orange and red)
The colour of a star is related to the star’s ____________ _____________
surface temperature
The force of gravity pulls the dust and gas together to form a protostar. The temperature rises as the star gets denser and more particles collide with each other.
What occurs when the temperature gets hot enough (around 15 million K)
Hydrogen nuclei undergo nuclear fusion to form helium nuclei.
This gives out huge amounts of energy!!
Which of the following will eventually become a supernova?
A stars with a similar mass to the Sun
B stars with a large mass than the Sun
C stars with a smaller mass than the Sun
B. stars with a larger mass than the Sun
Absolute magnitude is a measure of how bright a given star would appear to be if it were…
a fixed distance from the Earth.
True or False
’ A star that emits blue light will have a higher surface temperature than a star that emits red light’
True
True or false
‘Our Sun is a yellow star and has a core temperature of around 5000K’
False- our Sun has a surface temperature of 5000K.
Its core temperature will be about 15 million K and therefore fusion can occur in its core.
In a main sequence star, the outward pressure produced by nuclear fusion balances the force of gravity.
What causes this phase in the star’s life cycle to end?
The supply of hydrogen in the stars core, which is the fuel for nuclear fusion
Fusion ends when hydrogen runs out, meaning that the outward pressure no longer balances the gravitational force.
Where are the cool and bright stars found on the HR diagram?
Top right
Locate the red giants and red super giants in the HR diagram below.
C- red super giants - brighter than….
B- red giants
How does the time a star spends on the main sequence vary with the mass of a star?
The more massive a star, the shorter the time it spends on the main sequence. (they burn hotter and faster!)
