Types of Stars Life Cycle of Stars Galaxies Astronomy Types of Stars Life Cycle of Stars Galaxies

Characteristics of Stars Color Gas Composition Temperature Magnitude

Color/ Temperature A star’s surface temperature can be determined by their color Blue stars have a temperature above 30,000 K Red stars are much cooler Yellow stars have temperatures between 5000 and 6000 K (such as our Sun)

Binary Stars Binary Stars Pair of stars that orbit around each other Stars are kept together by gravity More than half of all stars are binary or clusters

Binary Stars: Sirius and its Tiny Companion

Taken from Hubble Space Telescope Star Cluster Taken from Hubble Space Telescope

Star Distance Measurement A light-year is the best unit to express stellar distance. It is the distance light travels in one year. Example: A star that is 4.3 light-years away means that it takes 4.3 years for light from that star to reach our Sun.

Magnitude This is how bright the star is (or appears to be) It can appear brighter if… The star is really close to Earth Actual brightness usually depends on size

Hertzsprung–Russell Diagram Makes no sense without caption in book

Hertzsprung-Russell Diagram Shows relationship between a star’s magnitude and temperature Main-Sequence line– as magnitude increases, so does temperature Notice how stars are colored blue, red, and yellow!!!

Hertzsprung–Russell Diagram Makes no sense without caption in book

H-R Diagram Almost 90% of all stars belong on the main-sequence The brighter stars are the hottest (blue) 50 times more massive than Sun

H-R Diagram Continued In the upper right corner of diagram are the red giants Large red giants are called supergiants (Betelgeuse in constellation Orion) In the lower-central part of diagram are the white dwarfs

Hertzsprung–Russell Diagram Makes no sense without caption in book

Where it all starts… Cloud of Gas and Dust

Birth of a Star Clouds of dust and gas in space 92% Hydrogen and 7% Helium All stars must have started with these gases. These clouds are also known as “nebula”

The Famous Eagle Nebula First taken by the Hubble Space Telescope in 1995

Orion Nebula

Gravity is important!! Gravity squeezes particles into the center of the cloud of dust and gas Without gravity, stars would not develop!!

Balanced Forces Makes no sense without caption in book

Nuclear Fusion A star is born once nuclear fusion has begun Nuclear fusion is the process of combining atoms to create tremendous amounts of energy. The first atoms to combine are hydrogen. They combine to create helium.

Main-Sequence Stage Stars age at different rates while in the main-sequence Hot, massive blue stars burn their hydrogen really fast Yellow stars (our sun) are in this stage for 10 billion years Remember: Our sun is only 5 billion years old…. So it still has 5 billion years left just in this stage!!

Yellow Star- Our Sun

Red-Giant Stage Star expands 100’s to 1000’s size of main-sequence star Convert helium to carbon to produce fuel and delay death Eventually all usable elements will be burned Yellow stars (sun) usually spend less than a billion years as a red giant

Burnout and Death A star’s life cycle depends on the star’s mass. Medium Mass Stars and Massive Stars will evolve and die differently

Medium-Mass Stellar Death Medium-Mass Stars (our sun) Become red giants During collapse as red giant, create a round cloud of gas known as a “planetary nebula” End as white dwarfs The leftover centers of the star

Taken from Hubble Space Telescope Planetary Nebula Makes no sense without caption in book Taken from Hubble Space Telescope

Taken from Hubble Space Telescope Planetary Nebula Taken from Hubble Space Telescope

High-Mass Stellar Death High-Mass Star Red Giant implodes and creates a supernova The gravity becomes too strong for the star to withstand Extremely rare The last supernova to be seen with the naked eye was in 1987. The explosion actually began before civilization began here on Earth, but it took 169,000 years for the light from the explosion to reach Earth.

Crab Nebula in the Constellation Taurus Makes no sense without caption in book Taken from Hubble Space Telescope

Taken from Hubble Space Telescope Supernova Taken from Hubble Space Telescope

Taken from Hubble Space Telescope Supernova Remnant Taken from Hubble Space Telescope

Star Remnants Black Holes Remnants of supernova event These remnants are so massive that they collapse Gravity is so strong that light can not escape Black holes do not “swallow up” other stars However, some of the gas and dust from the star may spiral into the black hole. Black holes were first “seen” by x-ray waves.

Black Hole Artists’ Drawing

Black Hole Makes no sense without caption in book

Review Medium-Mass Stars Massive Stars Cloud of gas and dust Main-Sequence Red Giant Planetary Nebula White Dwarf Massive Stars Cloud of gas and dust Main-Sequence Supergiant Supernova Blackhole

Galaxies A galaxy is a group of stars, dust, and gases held together by gravity The smallest galaxies still contain a few million stars. Galaxies were first classified by Edwin Hubble in the 1920’s Three types of galaxies Spiral Elliptical Irregular

Types of Galaxies Spiral Disk-shaped with arms extending from center 30% of galaxies are spiral Our galaxy, the Milky Way Galaxy The outer edges of the spiral are blue because most of the blue stars in this galaxy are located on the spiral’s “arms” The yellow and red stars are located in the middle

Spiral Galaxy

Spiral Galaxy www.hubblesite.org

Milky Way Galaxy Earth’s galaxy Large spiral galaxy 100,000 light-years wide and 10,000 light-years thick

Structure of the Milky Way Makes no sense without caption in book

Galaxies Continued Elliptical Range in shape- round to oval 60% of all galaxies are elliptical These have very bright centers

Elliptical Galaxy http://www.angelfire.com/id/jsredshift/images/arp135.jpg

Elliptical Galaxy http://www.glyphweb.com/esky/default.htm?http

Galaxies Continued Irregular No uniform shape 10% of galaxies are irregular Our nearest galaxy

Irregular Galaxy Makes no sense without caption in book

Irregular Galaxy http://www.edmar-co.com/adriano/ccd/ccd3.htm

The Big Bang Theory Theory about the origin of the universe At one time, the entire universe was confined to a dense, hot, supermassive ball. (To the size of a tennis ball!) Then, about 13.7 billion years ago, a violent explosion occurred, hurling energy in all directions Some of the expanding energy turned into matter Matter made nebulas, which then made stars. Stars eventually made galaxies.

The Big Bang Theory Makes no sense without caption in book

Supporting Evidence In 1964, Robert Wilson and Arno Penzias, using a giant radio wave antenna, found radiation that was coming to Earth from all directions in space Called “Cosmic Background Radiation” This radiation was actually created from the Big Bang.

Future for the Universe? Two possible futures: The Universe will expand forever (most popular) The outward expansion will stop and inward contraction will begin These are just theories--- no one is certain how the Universe began and if it will end.