Star Life CycleStar Life Cycle

Stellar Evolution: Life Stellar Evolution: Life of the Starof the Star The most massive stars The most massive stars

have the shortest lives. have the shortest lives. Stars that are 25 to 50 Stars that are 25 to 50 times that of the sun live times that of the sun live for only a few million for only a few million years. Stars like our Sun years. Stars like our Sun live for about 10 billion live for about 10 billion years. Stars less massive years. Stars less massive than the Sun have even than the Sun have even longer life spanslonger life spans

Stars are like humans Stars are like humans they are born, live and they are born, live and die die

Stars are formed in 1. Nebulae, interstellar clouds of dust and gas (mostly hydrogen).

These stellar nurseries are abundant in the arms of spiral galaxies.

In these stellar nurseries, dense parts of these clouds undergo gravitational collapse and compress to form a rotating gas globule.

The Birth of Stars

It begins to spin as it shrinks

NEBULA PICTURESNEBULA PICTURES

Protostar stage: The nebula flattens and the center condenses:

Temps start to increase due to friction (more collision of molecules).

When temps reach 10 million K, NUCLEAR FUSION begins

Nuclear Fusion generates the energy for a star.

When fusion begins, it is officially considered a STAR. (yeah!)

Fusion – combining a lightweight nuclei into a heavier nuclei

Protostar Protostar PicturesPictures

Stars live out the majority of their lives in a phase termed as the Main Sequence. Longest stage of a star

The protostar is now a stable main sequence star which will remain in this state for about 10 billion years. After that, the hydrogen fuel is depleted and the star begins to die.

Main-Sequence Stage

Main Sequence Star Main Sequence Star

When a star has burned between 10% and 20% of its hydrogen, its core will to run out of fuel.

At this stage, the star is entering the end of its life.The diameter of the star can increase by a factor of 200, while its cooling is translated into a reddening of its radiation : the star is

becoming what is called a red giant.

RED GIANT STAGE

Star has Star has run out of run out of HydrogenHydrogen atoms in the atoms in the corecore to undergo fusion. to undergo fusion.

Our sun has used only Our sun has used only about about 5%5% of its Hydrogen of its Hydrogen

Star Star expandsexpands about 10x about 10x bigger and bigger and coolscools..

Its luminosity Its luminosity increasesincreases, , temp temp decreasesdecreases.*****.*****

Helium fuses to form Helium fuses to form Carbon, and the core Carbon, and the core shrinks.shrinks.

It begins losing It begins losing outer outer layerslayers

BETELGEUSE –RED BETELGEUSE –RED GIANTGIANT

Only a few million Only a few million years old, Betelgeuse years old, Betelgeuse is already dying. is already dying. Astronomers predict Astronomers predict that it's doomed to that it's doomed to explode as a soon, explode as a soon, within 1,000 years or within 1,000 years or so, an event that will so, an event that will be spectacular for be spectacular for Earth's future Earth's future inhabitants. inhabitants. (Conceivably, it's (Conceivably, it's already happened as already happened as Betelgeuse is 640 Betelgeuse is 640 light-years away!)light-years away!)

  

F.Y.I.

•Star size comparison

Burnout and DeathBurnout and Death Fate of a Star Fate of a Star

depends on its massdepends on its mass All stars, regardless All stars, regardless

of size, run out of of size, run out of fuel and collapse fuel and collapse due to gravitydue to gravity

A star will A star will become either become either a black dwarf, a black dwarf, neutron star, neutron star, or black hole, or black hole, depending on depending on how massive it how massive it was. .was. .

Death of low-mass starsDeath of low-mass stars

Never evolve into red giantsNever evolve into red giants Remain stable main-sequence stars Remain stable main-sequence stars

until hydrogen is gone until hydrogen is gone Collapse into white dwarfsCollapse into white dwarfs

**Death of medium-mass **Death of medium-mass stars**stars**

Sun-like StarsSun-like Stars

(Mass under 1.5 times the mass of the (Mass under 1.5 times the mass of the Sun)Sun) Red Giant --> Planetary Red Giant --> Planetary Nebula -->White Dwarf Nebula -->White Dwarf

--> Black Dwarf--> Black Dwarf

**Death of massive **Death of massive stars**stars**

Huge StarsHuge Stars (Mass between 1.5 to 3 times the mass of the (Mass between 1.5 to 3 times the mass of the

Sun)Sun) Red SuperGiant --> Supernova --> Red SuperGiant --> Supernova -->

Neutron Star Neutron Star Giant StarsGiant Stars (Mass over 3 times the mass of the Sun)(Mass over 3 times the mass of the Sun)

Red SuperGiant --> Supernova Red SuperGiant --> Supernova --> Black Hole--> Black Hole

PLANETARY NEBULAPLANETARY NEBULA

This is left when a This is left when a giant loses its giant loses its outer layers of gas.outer layers of gas.

Leaves only the Leaves only the corecore.. The core will become a The core will become a white dwarfwhite dwarf

Planetary nebula Planetary nebula picturespictures

WHITE DWARFWHITE DWARFOnly hot, Only hot, dense core is left of this stardense core is left of this star.. It will shine for billions of years It will shine for billions of years before before

cooling.cooling. Stable star with no nuclear fuel,radiates Stable star with no nuclear fuel,radiates

left over fuel for billions of yearsleft over fuel for billions of years Could become a Could become a black dwarfblack dwarf, but the , but the

universe is not old enough to form theseuniverse is not old enough to form these

White Dwarf PicturesWhite Dwarf Pictures

SUPER NOVASUPER NOVA

Super Giant Super Giant eventually loses its eventually loses its outer layers in an outer layers in an explosionexplosion leaving leaving only the core – this only the core – this is the is the super novasuper nova..

Eventually this core collapses (in an instant). As the iron atoms are crushed together in this gravitational collapse, the core temperature rises to about 100 billion degrees.

The repulsive electrical forces between the atoms' nuclei overcomes the gravitational forces, causing a massive, bright, short-lived explosion called a supernova. During the explosion, shock waves, blow away the star's outer layers.

NEUTRON STARNEUTRON STAR

After a Super Nova explosion, After a Super Nova explosion, the core may the core may condense into a small core of neutrons.condense into a small core of neutrons.

It is so dense – 1 spoonful of Earth It is so dense – 1 spoonful of Earth would would weigh 100 million tons.weigh 100 million tons.

Rotates Rotates very rapidlyvery rapidly..If the star's remaining mass is between 1 1/2 If the star's remaining mass is between 1 1/2

to 3 times the mass of the Sun, it will to 3 times the mass of the Sun, it will collapse into a small, dense collapse into a small, dense neutron starneutron star (about ten miles in diameter, about 1.4 (about ten miles in diameter, about 1.4 times the mass of the Sun, with an times the mass of the Sun, with an extraordinarily strong magnetic field, and extraordinarily strong magnetic field, and rapid spin). rapid spin).

Neutron Star PicturesNeutron Star Pictures

BLACK HOLEBLACK HOLE

This is the This is the 33rdrd predicted result to a star. predicted result to a star. This is the This is the most dense coremost dense core of a star of a star

that can be left.that can be left. Gravity is so strong, Gravity is so strong, light cannot light cannot

escapeescape.. Makes it look like a Makes it look like a dark hole in dark hole in

spacespace..If the star's remaining mass is greater If the star's remaining mass is greater

than three times the mass of the Sun, than three times the mass of the Sun, the star contracts tremendously and the star contracts tremendously and becomes a becomes a black holeblack hole

Black Hole PicturesBlack Hole Pictures

Anatomy of a black hole

The density of a star is pre-The density of a star is pre-determined based on its weight determined based on its weight ((the amount of dust and gasthe amount of dust and gas) it ) it begins with.begins with.

Smaller stars become Smaller stars become white white dwarfsdwarfs..

Very large stars become Very large stars become neutron neutron starsstars or or black holesblack holes..

•Life Cycle of a Star Video