Lecture 9 - Stellar Evolution Flashcards
(20 cards)
How do stars form?
Stars form from dense clouds of dust and gas. After the Big Bang, most material was hydrogen with a small amount of helium. These elements formed clouds, which collapsed under gravity. The hydrogen eventually fuses into helium, forming a protostar.
What are Bok globules?
Small, dense fragments of gas and dust that form as larger clouds condense. They play a role in star formation.
What is a protoplanetary disk?
disk of gas and dust surrounding a forming star. As nuclear fusion begins, the star emits heat and light, evaporating much of the disk
Do stars form individually or in groups?
A single collapsing gas cloud can fragment, forming many stars at once. Star clusters contain stars of the same age but different masses
What happens when a star exhausts its hydrogen fuel?
Its core collapses, increasing temperature. Hydrogen in surrounding layers begins burning, expanding the star and cooling its surface.
What is the helium flash?
A sudden increase in fusion as helium ignites in the core, stabilizing burning for a time.
How do high-mass stars evolve differently?
They can fuse heavier elements beyond helium. Once iron forms, fusion stops, leading to gravitational collapse.
What happens when fusion stops in a high-mass star?
The core collapses into a neutron star or black hole, and outer layers explode in a supernova.
What are Population I, II, and III stars?
- Pop III: First-generation stars, mostly hydrogen and helium.
- Pop II: Contain metals from Pop III explosions.
- Pop I: Current-generation stars with higher metallicity.
How does an H-R diagram show stellar evolution?
It tracks the lifecycle of stars, showing temperature, luminosity, and age based on stellar properties.
What causes a nebula to collapse and form a star?
Gravity pulls the gas and dust together, causing the cloud to condense. Increased density leads to heating, eventually triggering nuclear fusion.
What is a protostar?
A young star in its early formation phase, before nuclear fusion begins. It continuously collapses and heats up until fusion starts.
How do low-mass stars end their life cycle?
They expand into red giants, shed their outer layers as planetary nebulae, and leave behind a cooling white dwarf.
What happens when a massive star reaches iron in its core?
Iron cannot undergo fusion to produce energy, leading to core collapse and the formation of either a neutron star or a black hole.
What causes a supernova explosion?
When a high-mass star collapses, its core shrinks rapidly, triggering a shockwave that blasts outer layers away.
What is electron degeneracy pressure?
A quantum effect that prevents further gravitational collapse in white dwarfs by resisting compression.
How does neutron degeneracy pressure affect stellar remnants?
It supports neutron stars against gravitational collapse, preventing further shrinkage unless mass exceeds the limit.
Why do high-mass stars have shorter lifespans?
Their higher temperatures allow them to fuse hydrogen more rapidly, burning through their fuel much faster.
What happens in a black hole?
Gravity is so strong that not even light can escape, and all matter collapses into a singularity.
How do population III stars differ from current stars?
They were the first stars, made almost entirely of hydrogen and helium, with no heavy elements.
