Star Life Cycle: From Protostar to Black Hole, Study Guides, Projects, Research of Astrophysics

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ƒ^ What^ percentage

of^ stars^ you

can^ see^ in

the

nighttime

sky^ are^ located

in^ our^ solar

system?^ ƒ^ 0%^ ƒ^ 100%^ ƒ^ 0.0000000001%^ ƒ^ 50%

ƒ^ All^ stars^ follow^ a^ very

specific^ life

cycle.

ƒ^ All^ stars^ begin^ in^ the

same^ way. ƒ^ The^ size^

of^ the^ star^

determines

how^ the^ star

will

“die.” ƒ All^ stars^ begin

their^ lives^ in^ a^ stellar^

nebula^ as^ cool

clouds^ of^ gas

and^ dust. ƒ^ Once^ the

cloud^ of^ gas

and^ dust^ begins

collapsing in

on^ itself,^ it^

becomes^ a

protostar.

ƒ^ The next stage of a star’s life is called

Main

Sequence ƒ Main sequence stars are stars, like our Sun, that fusehydrogen atoms together to make helium atoms intheir cores. ƒ Since stars have a limited supply of hydrogen in theircores, they have a limited lifetime as main sequencestars. ƒ The amount of mass and the luminosity, or brightnessof stars, determines the length of their lives.

ƒ^ Stars^ the

size^ of^ our

sun^ or^ smaller

become^ red

giants. ƒ As^ hydrogen

in^ the^ core

is^ consumed,

the^ core^ of

the^ star^ loses

gravity. ƒ^ Eventually,

the^ outer^ parts

of^ the^ star

expand^ away

from^ the^ core

and^ its^ decreased

gravity.

ƒ^ Red^ giants

eventually

become^ planetary

nebula

where^ the^ outer

layers^ of^ the

star^ are^ blown

away

leaving^ only

the^ hot,^ dense

core

ƒ^ After^ becoming

a^ planetary

nebula,^ the

remains^ of

the^ core^ of

the^ star^ become

a^ white^ dwarf. ƒ^ A^ white^ dwarf

is^ a^ star^ that

has^ exhausted

most^ or

all^ of^ its^ nuclear

fuel^ and^ has

collapsed^ to

a^ very

small^ size;^

such^ a^ star is^ near^ its^ final

stage^ of^ life.

ƒ^ White^ dwarfs

eventually

become^ black

dwarfs,

which^ is^ a^ white

dwarf^ that

has^ cooled

down^ enough

that^ it^ no^ longer

emits^ light. ƒ^ Interesting

Fact:^ The^ universe

is^ not^ old^ enough

to

have^ any^ black

dwarf^ stars

yet.

ƒ^ Eventually

Red^ Super

Giants^ will

explode^ in

something

called^ a^ Supernova. ƒ^ A supernova occurs when a star withmany times the mass of the Sun runs outof usable nuclear fuel. ƒ^ The^ Crab Nebula

is an example of the remnants of supernova.

ƒ^ Neutron stars^ are^ the

collapsed^ cores

of^ some

massive^ stars.

They^ pack roughly^ the

mass^ of^ our

Sun^ into^ a^ region

the^ size^ of

a^ city. ƒ^ Black^ Holes

form^ from

the^ most^ massive

of^ stars.

ƒ^ Black^ holes

have^ such^

strong^ gravity

that^ nothing,

not^ even^ light,

can^ escape

their^ grip.

ƒ^ Read^ pages

40 ‐^45

ƒ^ Draw^ a^

star^ life^ cycle

flow^ chart

in^ your

notebook.

(similar^ to

previous^

slide)^ Include

all^ stages

discussed

in^ class.

ƒ^ Pay^ particular

attention

to^ the^ H‐

R^ diagram

information

on^ pages

‐43.^ You^ MUST

understand

the^ information

this^ diagram

presents.