life cycle of a star all stars begin the same way: before life as a star nebula a nebula is a cloud...

Life Cycle of a Life Cycle of a StarStar

All Stars Begin the Same All Stars Begin the Same Way:Way:

Before life as a star Nebula

A nebula is a cloud of interstellar dust, hydrogen and helium gas, and plasma

All Stars Begin the Same All Stars Begin the Same Way:Way:

1st Stage of Life – the Protostar

Ball of gas and dust that is pulled together by gravity

Nuclear fusion starts as gas cloud becomes denser and hotter

Nuclear Fusion hydrogen atoms fuse into helium

Creates the intense energy found in stars

The Life Cycle Depends The Life Cycle Depends on Starting Masson Starting Mass

ProtostarMain SequenceWhite DwarfBlack Dwarf

ProtostarMain SequenceRed GiantWhite DwarfBlack Dwarf

ProtostarMain SequenceSuper GiantSupernova

neutron star black hole

Small Mass Medium Mass Large Mass

Main Sequence StageMain Sequence Stage

longest stage

hydrogen fuses into helium which creates enormous amounts of energy (nuclear fusion)

the size of the star does not change much

this is the stage our sun is currently in

“middle age”

Main Sequence StageMain Sequence Stage

Remember, all stars go through a main sequence stage

Large Mass stars = large main sequence stars

Medium Mass stars = medium-sized main sequence stars

Red GiantsRed Giants

Red GiantsRed Giants

This Stage Happens for Medium Mass Stars Onlyoccurs when star begins running out of hydrogen – it starts cooling and expanding at the same timecenter shrinks and atmosphere swells

Red GiantsRed Giants

the end of the red giant stage occurs when the atmosphere of the star becomes so spread out it slowly dissipates

this stage is called “planetary nebula”

Red GiantsRed Giants

planetary nebulawhite dwarf

White DwarfsWhite Dwarfs

White Dwarf small hot star that is the leftover center of an older star

Can shine for billions of years before they extinguish

White DwarfsWhite Dwarfs

SupergiantsSupergiants

Stage That Happens For Large Mass stars only

occurs when star begins running out of hydrogen – it starts cooling and expanding at the same time

center shrinks and atmosphere swells

looks a lot like a red giant, doesn’t it?

SupergiantsSupergiants

the big difference is thesizeand brightness

supergiants are up to 1,000,000 times brighter than the sun

medium star

Jupiter

large mass star

Relative Size of StarsRelative Size of Stars

Giant stars

SupernovaSupernovaSupernova

gigantic explosion in which a massive star collapses

occurs after a massive star uses up its fuel source

supernova

Neutron Star

Neutron Star

A neutron star that spins and sends out beams of radiation is called a pulsar

a star that has collapsed to a point at which all particles are neutrons

Black HoleBlack Hole

Black Hole

an object that is so massive that light cannot escape its gravity

Astronomers can detect black holes by using X-ray telescopes

Neutron Star or Black Neutron Star or Black Hole?Hole?

Black Hole Neutron Star

~ 8 to 15 solar masses > 15 solar masses

SummarySummary

Observe life of a star

Recall:

Comprehend:

Apply:

S T A R

S

S

T

T

A

A

R

R

What is the longest stage for any star?

All stars remain in their Main Sequence stage longer than in any other stage

What are neutron stars made of?

Neutron stars are made of neutrons. A neutron star is so dense that a teaspoonful would weigh 1 billion tons!

What kind of stars form a supernova?

Only large mass stars form supernova.

What kind of stars form red giants?

Medium mass stars like our sun form red giants.

What size of stars will form black holes?

Only stars with 15 solar masses or larger will form black holes.

What kind of stars “skip” the red giant /supergiant phase altogether?

Small mass stars go straight from their main sequence stage to white dwarf

What stages do all stars have in common?

All stars begin as nebula, become protostars and then become main sequence stars.

What kind of stars are smaller than Earth?

Both white dwarfs and neutron stars are smaller than Earth.

What is the one factor that determines the ultimate fate of a star?

The mass of a star determines its fate.

Which main sequence stars are larger than the Earth?

All main sequence stars are larger than Earth.

Why won’t our sun ever become a black hole?

Our sun will never become a black hole because it does not have enough mass.

How many times larger would our sun have to be to supernova?

It takes a star that is at least 8 solar masses to be massive enough to supernova, so our sun would have to be at least 8 times as large.

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