Life Cycle of Stars

New Solar System

Life Cycle of Stars

Fetus (Stellar Nebula Stage)

• Nebulae are huge

clouds of gas and dust

(singular: nebula)

• Stars form in nebulae

by the force of gravity

• Nebular gas and dust

are from an exploded

star.

Fetus -- Proto-Star Stage

• Hydrogen and

helium are the main

gases in stars.

• The proto-star

begins to spin and

glow - temperature

increases.

Birth - Maturity of Stars --

Main Sequence Stage

• Fusion occurs – hydrogen atoms are fused into helium, giving off tremendous energy.

• The force of gravity is in equilibrium (balanced) with the energy from fusion.

• Most stars will spend 90% of their life cycle as main sequence stars

Maturity - Main Sequence

Hot, Bright

Hot, Dim

Cool, Bright

Cool, Dim

Maturity - Main Sequence

• Hertzsprung-Russell (H-R) Diagram

plots the surface temperature of stars

against their luminosity

– Luminosity = the total amount of energy a

star gives off each second

– Hottest stars are brightest

– Coolest stars are dimmest

– Most stars reside in the main sequence

• A diagonal pattern from lower right to upper left

H – R Diagram

Where would

dying stars plot

on the diagram?

Point A

Point B

Where would

stable stars plot

on the diagram?

Point C

Where would

dead stars plot

on the diagram?

Mid-life Crisis -- Red Giant / Red Supergiant Stage

• Hydrogen in the core is

used up

• The star fuses heavier

elements, like carbon.

• Star becomes unstable

as the forces of fusion

and gravity are no

longer equal.

• Cooler in temperature.

Hydrogen-to-helium fusion stops

Old Age -- Supernova and Planetary Nebula

• Massive Stars go Supernova:

• Helium is fused into Iron

• Sun-like stars become

Planetary nebulae:

• Fusion of elements up to

carbon occurs in the core.

• Outer layers lift off

Death : Average Stars --

White Dwarf Stage

Average Sun-Sized Stars

• All fuel is used up.

• Red Giant collapses into a

white dwarf as gravity wins

over fusion.

• Dim, faint star with high

temperature.

• Sun-like star becomes white

dwarf made of carbon.

• Black Dwarf – no energy –

cools – turns black

A diamond weighing 10

billion trillion trillion carats

is at the heart of a dead

white dwarf star

nicknamed Lucy.

It’s 50 ly from us, in the

constellation Centaurus.

Death: Massive Stars -- Supernova Stage

• Massive stars, much larger than our sun,

have a different life cycle.

• Giants and super giants will explode as a supernova.

• Some massive stars collapse to form black-holes or become a neutron star.

• Black holes occur with VERY massive stars – Strong gravity, all matter trapped

• Neutron stars – all elements join – Removing all space, making incredibly dense

star

The Milky Way…look alike

Closest

Galaxy

to us?

Milky

Way

Hubble Space Telescope

Named after Edwin Hubble

Pictures of Supernovae

Hubble Photos

Visible Light

Infrared Light

Stars can be grouped into

Constellations.

• Ancient civilizations never grouped planets

with stars because planets are constantly in

motion, whereas stars are in a fixed position

and pattern.

Polaris – the North Star

Andromeda Galaxy