Stellar Evolution Flashcards
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
A hot star will emit most its visible light at the _____________ frequencies of visible light.
highest (blue)
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)
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!!
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.
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!)
The Sun is a yellow star. What colour would a lower surface temperature star be?
red
The Sun is a yellow star. What colour would a higher surface temperature star be?
blue
Stars initially form from a cloud of dust and gas called a….
nebula
Which process releases energy in stars?
A. Combustion
B. Nuclear fission
C. Nuclear fusion
C. Nuclear Fusion
This occurs in the core of a star which is at more than 15 million Kelvin.
