Stellar evolution Flashcards
Understand the life cycle of low-mass and massive stars.
Out of which elements are stars initially formed?
Hydrogen(78%) and Helium (21% of the material in the universe)
What’s a star’s first stage?
By an accreting collection of Hydrogen and Helium gas, the first stage is called a “protostar.”
What’s the last stage of a star called?
It could either be a white dwarf, neutron star or black hole.
What does the difference in binding energy of the nuclei of a star suggest?
The process releases energy, often as electromagnetic radiation, to heat the star.
What holds up a star’s structure against gravitational collapse?
The pressure from the vibration of its particles and the electromagnetic radiation trying to escape.
The constant battle between these two drive the evolution of a star.
What determines the possible lifecycle a star will follow?
The initial mass of a star.
Out of the multiple possible life cycles for stars, what are the 2 paths that they are usually grouped into?
Life cycles for low-mass stars (like our sun) and that of “massive stars,” which have at least 4 times the mass of our sun.
Why have we not seen any black dwarfs?
Because this stage is theoretical. It takes a white dwarf longer than the current age of the universe to cool this much. So there has not yet been time for these to develop.
How much of a mass do low-mass stars accrete?
About the mass of our sun.
What are the features of a l-m star when it undergoes nuclear fusion?
The fusion of Hydrogen converts it to Helium.
The star is at this point in a stable stage of life, in which radiation pressure and gravity are in equilibrium.
The star remains in this state for billions of years.
What happens in a l-m star when it runs low on fuel?
It expands slightly, after having produced so much energy.
What happens as a result of the expansion of a l-m star?
Causes temperature to fall, the star becomes a red giant.
What does the l-m star do once most of the Hydrogen fuel is used?
It starts fusing Helium nuclei. This causes an explosion that throws some material from the star out into space, forming a planetary nebula.
What happens in the l-m star when fuel runs out?
The outward pressure from fusion is defeated by gravity. The star is then caused to contract resulting in an increase in heat. It becomes a white dwarf.
How does a l-m star die?
As time passes, it dies when it loses its energy. It passes through the red dwarf stage to become a black dwarf.
