Life Cycle of a Star

All Stars Begin the Same 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 Way: 1 st 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 on Starting Mass Protostar Main Sequence White Dwarf Black Dwarf Protostar Main Sequence Red Giant White Dwarf Black Dwarf Protostar Main Sequence Super Giant Supernova neutron star black hole Small MassMedium MassLarge Mass

Main 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 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 Giants

This Stage Happens for Medium 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

Red 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 Giants planetary nebula white dwarf

White 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 Dwarfs

Supergiants 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?

Supergiants the big difference is the size and brightness supergiants are up to 1,000,000 times brighter than the sun medium star Jupiter large mass star

Relative Size of Stars Giant stars

Supernova Supernova  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 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 Hole? Black HoleNeutron Star ~ 8 to 15 solar masses> 15 solar masses

Summary Observe life of a star Recall: Comprehend: Apply: STAR 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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