Stellar Evolution

Mass:

the most important factor in determining the life of a star.

Gravity & Internal heat:

balance that determines evolutionary stage of a star's life.

H-R diagram:

useful to map evolution of star's life

Inhibitors to cloud collapse:

heat, rotation, and magnetism

Triggers to cloud collapse:

nearby supernova explosion and clouds colliding

Cloud Fragmentation:

reason why young stars form in clusters.

Proplyd:

proto-planetary disk.

Why must we use IR to view early star formation?

protostars emit mot of their light in the IR and IR can be seen more easity through dusty clouds.

T Tauri Star:

a proto star.

Progress of star formation using nebula types:

dark, emission, reflection, bare.

When does a proto star become a star?

when it begins fusion in its core and stabilizes.

Where do high mass stars end up on the main sequence?

upper left.

Where do low mass stars end up on the main sequence?

lower right.

Do stars evolve on the main sequence?

no.

Why are most stars found on the Main Sequence of an H-R diagram?

it's the longest part of a star's life.

What is happening on the main sequence?

H to He fusion in the core.

High mass stars:

core processes and interior layers differentiate.

Low mass stars:

basically the same as the sun.

Why do massive stars live shorter lives?

they are hotter and burn fuel faster.

CNO cycle:

new fusion cycle for high mass stars; 4H->1He.

How does convection effect main sequence stars?

acts as a giant mixer with H from outer layers and H in the core; replenishes H fuel in core.

What happens to the core and envelope of a star when H fusion stops?

core contracts and becomes denser and hotter, while pushes on the envelope causes it to expand.

What happens on the sub-giant branch?

expansion diffuses surface heat and star appears cooler.

Red-giant branch:

collapsing He core, expanding envelope.

Horizontal branch:

helium to carbon fusion in the core, stable envelope

Asymptotic giant branch

collapsing carbon core, expanding envelope

Electron degenracy pressure

powerful pressure produced by repulsion of closely packed electrons.

Planetary nebula

outer layers that have exploded off a star.

White dwarf

very hot star with a dense and small core

Black dwarf

invisible star

The inside of a high mass star just before a supernova?

nothing but neutrons

Why can't a star fuse past iron normally?

iron fusions absorb energy

Progression of a supernova:

-rapid collapse
-expansion
-neutrons collide in center, bounce
-bounce creates a huge explosion

How do we get elements stronger than iron?

supernova

Stellar nucleosynthesis:

formation of elements in the stars

Why do we have more even # elements than odd?

predominant fusion processes adds 2 to the atomic #

Instability strip:

on H-R diagram where oscillation occurs and there is just the right amount of heat and pressure

What causes variability for Cepheids and RR Lyrae type stars?

mass

Why are Cepheids and RR Lyrae type stars useful?

very bright and you can see them from far away.

How can we use star clusters to prove stellar evolution theories?

measure temperature and luminosity of stars and compare on a graph.

How can we use star clusters to determine age?

most stars in clusters are same age, but evolve differently.

Algol paradox:

situation where a giant star has less mass than a main sequence star.

How was the algol paradox resolved?

binary systems stars which pull materials off the more massive star and becoming more massive itself.

What is so useful about observations of Herbig-Haro objects and T Tauri stars?

evidence for star formation by collapse of nebula

What defines the beginning of a stars life on the main sequence?

fusion

What causes variability in the brightness of stars in the instability strip?

pulsation

Main sequence turn off point:

used to determine age of star clusters.