N O T T H O S E T Y P E S O F S TA R S !

LIFE CYCLE OF STARS

WHAT IS A STAR?

• Star = ball of plasma undergoing nuclear fusion.• Stars give off large

amounts of energy in the form of electromagnetic radiation. • An x-ray image of

the sun.

THE FIRST STEP!

• Stars are formed in a Nebula. • A Nebula is a very large cloud of gas and dust in space.

Orion Nebula

PROTOSTARS

• Dense areas of gas in the nebula collect due to gravity.• The dense areas of

gas take on a definite shape called protostars.

PROTOSTAR

• As gas is added, the pressure in its core increases.• Causing the gas molecules to move

faster, increasing friction.• Causing heat to be generated, increasing

core temperature leading to fusion.

NUCLEAR FUSION

• Nuclear Fusion: process by which two nuclei combine to form a heavier element.• New stars initially

will fuse hydrogen nuclei to form helium.

MAIN SEQUENCE STARS

• Results when protostar starts fusion• They fuse hydrogen to form helium, releasing enormous amounts of energy.• It takes about 10 billion years to consume all the hydrogen in a Main Sequence star.• The sun is a main sequence star!

RED GIANTS

• Collapsing outer layers cause core to heat up.• Fusion of helium into carbon begins.• Outer shell expands from 1 to at least 40

million miles across. ( 10 to 100 times larger than the Sun)• Red Giants last for about 100 million

years.

DYING A SLOW DEATH – MASS MATTERS

Red Giant

Mass < 3 x sun

White Dwarf

Black Dwarf

Mass > 3x sun

Red Super Giant

Super Nova

Neutron Star

Black Hole

WHITE DWARFS

• Fusion stops• The core is now very

dense and very hot. (A tablespoon full would weigh 5 tons!)• The core begins to

cool.• A white dwarf is

about 8,000 miles in diameter.

BLACK DWARFS

Eventually white dwarf cools to point where it emits no visible light

A black dwarf will continue to generate gravity and low energy transmissions (radio waves).

RED SUPER GIANTS

• If the mass of a star is 3 times sun or greater, the Red Giant will become a Red Supergiant.• Fuses carbon to iron.• The star will expand to be between 10 and

1000 times larger than our sun.

RED SUPER GIANTS

SUPERNOVA

• When a Supergiant fuses all of the Carbon into Iron, there is no more fuel left to consume.• The Core of the supergiant will then

collapse in less than a second, causing a massive explosion called a supernova.• A massive shockwave is produced that blows

away the outer layers of the star.• Supernova shine brighter then whole galaxies for

a few years.

SUPERNOVA

NEUTRON STAR

• Leftover core of super nova• If it has a mass of

less than 3 solar masses, then the core becomes a neutron star.

• 6 miles in diameter!

BLACK HOLES

• If the mass of the surviving core is greater than 3 solar masses, then a black hole forms.• A black hole is a core so dense and massive it will generate so much gravity that not even light can escape it.