The Universe: Galaxies, Stars, and Nebulae March 3, 2011

The Universe All physical matter and energy that exist in space: All physical matter and energy that exist in space: Planets Planets Stars Stars Galaxies Galaxies All the contents of intergalatic space All the contents of intergalatic space

A Planet Most scientist agree that a planet: Most scientist agree that a planet: Orbits a star – such as the Sun Orbits a star – such as the Sun Is round - due to the strength of its own gravitational pull Is round - due to the strength of its own gravitational pull

Galaxies NOT single stars – includes: Stars, Gas, and Dust NOT single stars – includes: Stars, Gas, and Dust Variety of shapes, sizes, and colors Variety of shapes, sizes, and colors Clustered in Groups Clustered in Groups Gravitationally attracted/held together Gravitationally attracted/held together

Galaxies Milky Way = part of Local Group Milky Way = part of Local Group 5 million light years across 5 million light years across In 1999 HST (Hubble Space Telescope) est. 125 billion galaxies; HST found 3,000 visible galaxies in space In 1999 HST (Hubble Space Telescope) est. 125 billion galaxies; HST found 3,000 visible galaxies in space

Galaxies Spiral = Milky Way Stars form “arms”, curve out from center, disk or pancake shaped Stars form “arms”, curve out from center, disk or pancake shaped Holds old & young stars, gas, & dust Holds old & young stars, gas, & dust

Galaxies Elliptical Stars form shape like a football Stars form shape like a football

Galaxies Irregular No special shape = blobs w/threads No special shape = blobs w/threads Holds large amount of gas and dust Holds large amount of gas and dust

Stars Large ball of gas that creates & emits its own radiation Variety of shapes, sizes, and colors Variety of shapes, sizes, and colors Nebula, Main Sequence, Red & Super Giants, White Dwarf, Brown Dwarf, & Supernova Nebula, Main Sequence, Red & Super Giants, White Dwarf, Brown Dwarf, & Supernova UM = M agnitude = degree of brightness UM = M agnitude = degree of brightness Lifecycle – NO star lives forever Born, Matures, Grows old, & Dies

Nebula – dense region inside begins to shrink, warm up, becomes a protostar nge.html A Star is born Protostar – critical temperature is reached – hydrogen begins fusing into helium Protostar – critical temperature is reached – hydrogen begins fusing into helium

Once a star is born it becomes a Main Sequence Star – shines as nuclear reactions inside produce light and heat Main Sequence Star – shines as nuclear reactions inside produce light and heat But if it doesn’t have enough mass to produce radiant heat it becomes a Brown Dwarf But if it doesn’t have enough mass to produce radiant heat it becomes a Brown Dwarf

At this point Stars can become a Super Giant or Red Giant Super Giant Star of greater mass Expands, cools, & turns red Star of greater mass Expands, cools, & turns red Super Giant EXPLODES blasting away outer layers becoming a Super Nova

Supernova can become either: Neutron Star – core collapses & becomes very dense Black Hole – core collapses completely & vanishes

If a Star becomes a Red Giant, then Red Giant – star of less mass expands, glows red as it cools, then Planetary Nebula – outer layer of gas puff off; hot core will be white dwarf space-uncovers-an-ancient-star/

Red Giant =Planetary Nebula = White Dwarf = White Dwarf Cooling White Dwarf – very dense, almost transparent White Dwarf Cooling – takes billions of years to cool then fades to black

Cooling White Dwarf = Black Dwarf Black Dwarf - A non-radiating ball of gas; star stops glowing