star birth occurs in a nebula. a star's initial mass determines the star’s temperature,...

Star birth occurs in a nebula A stars initial mass determines the starrsquos temperature luminosity and diameter that ultimately

decides which life stages and type of death it will experience

The larger the star the shorter its life will be

Hydrostatic Equilibrium a star must be very hot and dense inside to balance its own GRAVITY

TEMPERATURE inside a star governs the rate of nuclear reactions WHICH determines its LUMINOSITY (energy radiated by astronomical object seen by us as light)

The balance between gravity pushing inward and outwardpressure is maintained by heat due to nuclear reactions andcompression is called HYDROSTATIC EQUILIBRIUM

SOhellipIf a star expands or contracts hydrostatic equilibrium Is not in place

NEBULA

bull Large clouds of gas and dust that contract due to gravitational force as it becomes hotter

1st Stage of Life

Protostar

hot condensed object of gas and dust that is pulled together by gravity at the center of a nebula

it generates energy and shines but is NOT hot enough to ignite nuclear fusion

Nuclear Fusion hydrogen atoms fuse into helium creating the intense energy found in stars

2nd Stage

bull Main Sequence (the Sun)ndashLongest stage stable starndashHydrogen changes into helium which

creates enormous amounts of energyndashThe size of the star does not change

muchndash90 of all stars

A Star of a Jokehellip

A woman at a gas station noticed a spaceship landing in front of her An alien stepped out of the spaceship and started to pump gas into it The woman noticed the letters UFO printed on the side of the ship She turned to the alien and asked Does UFO stand for Unidentified Flying Object

The alien answered No it stands for Unleaded Fuel Only

3rd stageGiants and Supergiants

ndash Main Sequence star becomes a red giant

bull Red giant star that expands 50x their normal size and cools (giving it a reddish color) it loses all its hydrogen appears brighter

bull Supergiant Large star with high

mass that become even hotter and expanding even more

It is 100rsquos of times hotter and more luminous than a red giant

Supernova

bull gigantic explosion in which a massive star collapses

ndash Occurs after a massive star uses up its fuel source

Supernova Remnant

White Dwarf

bull small hot star bull Fuel is used up

ndashFinal stage for some starsndashCan shine for billions of

years before they completely cool and extinguish

Black Dwarf

bull The remains of a white dwarf after it has completely cooledbull Scientists donot think universeis old enough tohave any black dwarfs yet

Neutron Star

A neutron star is a type of remnant that can result from the gravitational collapse of a massive star during a supernova event

Small dense star-one teaspoon would weigh a billion tons on Earth

What is a Black Hole

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

Did you knowhellip

Astronomers can detect black holes by using X-ray telescopes

Pulsars

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

Hertzprung-Russell Diagram

Shows the relationship between a starrsquos surface temperature and absolute magnitude

ndash Used to study the lives of stars

ndash Most stars lie along the main sequence portion of the diagram

Our Place in Our Galaxy

Be careful about wishing on starshellip

Whatrsquos the Difference

Universe

Galaxy

Image credits NASA STScI

Solar System

Where is our Solar System

Visible stars gas dust in the Milky Way Galaxy

Image credits NASA STScI

Solar System

here

What Are Galaxies

bull A galaxy is a system of stars dust and gas held together by gravity

bull Galaxies are large collections of starshellip

millions and billions of stars

bull There are hundreds of billions of galaxies in the Universe

bull Millions to hundreds of billions of stars in each galaxy

Galaxy Factsbull The most distant galaxies ever photographed are as far as 10

billion to 13 billion light-years awaybull Large galaxies have more than a trillion stars bull Only three galaxies outside the Milky Way are visible with

the unaided eye People in the Northern Hemisphere can see the Andromeda Galaxy which is about 2 million light-years away People in the Southern Hemisphere can see the Large Magellanic Cloud which is about 160000 light-years from Earth and the Small Magellanic Cloud which is about 180000 light-years away

Rememberhellip

A light-year is the distance that light travels in a vacuum in a year -- about 588 trillion miles (946 trillion kilometers)

An astronomical unit is 93 million miles or 150 million km (average distance between Sun and the Earth)

The speed (velocity) of light is 300000 kmsec

1048708Galaxies are classified based on shape

1 Spiral--rotating disk (with arms) 2 Ellipticalmdashspheroid or oval disk of

stars with more chaotic motion3 Irregular--none of the above

Three Main Types of Galaxies

Elliptical Spiral Irregular

Examples of Three Main Galaxy Types

Looking at the Milky WayA Spiral Galaxy

Viewed as a bright band of stars across the sky

There are about 200-400 billion stars in the Milky Way

Much of the Milky Way is blocked by dust seen as a dark band through the middle of the Milky Way1048708

The Milky Way ishellip

bull Gigantic Its disk spans 100000 light-yearsbull itrsquos about 14 billion years old give or take a few

billionndash Astronomers arrived at this age by measuring the age

of a single star The galaxy canrsquot be any YOUNGER than its oldest stars so this technique yields a MINIMUM age for the Milky Way

ndash Astronomers determined the starrsquos age by measuring its chemistry They found that it contains only minute traces of anything heavier than hydrogen and helium the two lightest elements

One of the most important tracers of the starrsquos age is a radioactive element called thoriumThe star contains only about half as much thorium as expectedThorium has a half-life of 14 billion years In other words in 14 billion years half the starrsquos thorium should have turned into other elements Since half of the thorium has disappeared astronomers deduce that the star is about 14 billion years old mdash and so is the Milky Way

If gasdust in a disk are rotating with the same speed stuff further out will take longer to go around and will lag behind

Spiral arms are a natural consequence of some rotations

Elliptical Galaxies

lack spiral arms and dust andcontain

stars that are

generally identified

asbeing old

Irregular GalaxiesIrregular galaxies lack any specific form and contain stars gas and dust