Astrophysics Flashcards
What is the first stage of the life cycle of a Star? [3]
- Solar system was originally a cloud of hydrogen and dust( nebula)
- After time passes, clumping occurs in dense regions due to gravity, and these dense hot regions begin to glow, forming a protostar
- Threshold temperature is reached in dense regions, so hydrogen fusion occurs(10^7C)
What happens in the main sequence stage of a Star? [2]
- The star is stable, as hydrogen fusion releases heat energy which keeps the core hot
- The thermal expansion of gas creates an equal outward pressure to the inward force of gravity, creating hydrostatic equilibrium
What happens to low-mass stars immediately after the Main Sequence stage?
- Eventually fusion in the core starts to die down, so the inward force of gravity exceeds the outward pressure, so the core will collapse and shrink and heat up, causing fusion reactions in the Helium core, pushing the light H-outer layers far out, so the outer surface cools and it becomes a red giant.
What happens long after the Main Sequence stage in a low-mass star? [2]
- The star will eventually become unstable and eject the outer layer of dust and gas, forming a planetary nebula.
- This leads to the core completely collapsing as it is left behind, so the star becomes a white dwarf, which cools to a black dwarf star.
What happens immediately after the Main Sequence stage in a high-mass star?
High-mass stars become red supergiants which produce iron in their core, so Gravitational Pressure> Radiation pressure because iron exerts no pressure on the core. So, eventually the star implodes and forms a supernova in a huge release of energy.
What happens to a high-mass star long after the Main Sequence stage? [2]
- The explosion of the supernova forms nuclei heavier than iron, so an incredibly dense neutron star will form
- With EVEN LARGER mass stars, the neutron star will collapse on its own gravity and form a black hole
What is on the x axis of the Hertzsprung-Russell diagram?[2]
- Temperature in Kelvin
- DECREASES as you go further up the axis, not increases
What is on the y axis of the Hertzsprung-Russell diagram?
Brightness
What do you find on the top right of the Hertzsprung-Russell diagram?
Supergiants
What would you find at the top left going in a diagonal line down on the Hertzsprung-Russell diagram?
Main Sequence Stars
What would you find at the bottom-left of the Hertzsprung-Russell diagram?
White Dwarfs
What would you find at the middle-right of the Hertzsprung-Russell diagram?
Giants
What can sometimes be found on the y axis of the Hertzsprung-Russell diagram?
Absolute Magnitude
What is apparent magnitude?
A measure of the brightness of an object from Earth
What is Absolute Magnitude? What is unique about it?
- A measure of the brightness of an object
- The brighter the star, the SMALLER the magnitude
