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1 STARS AND GALAXIES STARS enormous spheres of plasma formed from strong gravitational forces PLASMA the most energetic state of matter; responsible for the characteristic glow emitted by these heavenly giants STAR COMPOSITION mostly made up of the element hydrogen. Hydrogen atoms fuse together in the cores of stars through a process called nuclear fusion. When hydrogen atoms fuse, helium atoms, energy, and light are produced. STAR LIFE CYCLE stars only exist for a certain amount of time before they burn out. They each have their own life cycle.

2 LIFE CYCLE OF A STAR 1. PROTOSTAR birth of a star within a nebula, which is a huge cloud of dust and gas, gravitational forces cause dust and gas to collapse and become more dense as gravity pulls in more gas and dust from the surrounding nebula, the ball of material continues to collapse and become more and more dense if the force of the material pushing out equals the force of gravity making the material collapse, then fusion will take place and a star is born.

3 Once fusion occurs and the protostar becomes a star, the star has entered the main sequence 2. THE MAIN SEQUENCE A star spends the majority of its life fusing hydrogen into helium. This fusion keeps the star from collapsing under its own gravity and causes the star to shine and send out heat into space. As the star gets older and begins to run out of fuel, the outer layers of the star will start to expand as the star loses its flight with gravity. The star enters its red giant or super red giant stage (depending on how big the star originally was)

4 3. GIANT OR SUPER GIANT Once a star runs out of hydrogen fuel, the core begins to quickly contract and the star begins fusing helium into carbon to fight gravity. While this is happening, the outer layers of the star begin to expand quickly and the star takes on a much darker red color. This is why it is called a red giant in small and medium sizes and super red giant in larger stars. Once the star completely runs out of fuel, it is forced to give into gravity and the star dies. 4. DEATH OF A STAR Once a star runs out of fuel and is forced to give into gravity, the remaining material is collapsed inward by gravity very quickly. In small and medium sized stars, the star contracts as far as gravity can force it to and it becomes a white drawf. After it cools, which takes billions of years, a white dwarf comes a black dwarf. In larger stars, when fuel runs out and the material contracts, a huge explosion happens. Depending on the star size, this explosion is called a nova or super nova. Most of these large stars become neutron stars which are made of incredibly dense material and continue to give off radiation.

5 The largest stars will end their life by becoming a black hole. Black holes are dense and have such a strong gravitational pull that not even light can escape them. H-R Diagram (Hertzsprung-Russell Diagram) Tool that shows relationships and distances between stars Shows stars luminosity (light and temperature) Shows stars at different ages/stages at the same time WHAT IS A GALAXY? a. Large group of stars, gas, and dust in space that are held together by gravity b. Largest galaxies contain more than a trillion stars; smallest galaxies may have only a few million c. Scientists estimate the number of stars from the size and brightness of the galaxy.

6 1. Spiral Galaxies Shaped like flattened disks with one or more spiral arms Contain nebulas Our galaxy, the Milk Way, is a spiral galaxy i. Our solar system is located in one of the spiral arms ii. The Milky Way galaxy is one of the largest galaxies in the universe iii. Scientists used to believe that the Milky Way was a classic spiral galaxy, but they now believe it may actually be a Barred Spiral Galaxy Barred Spiral Galaxies are shaped like spiral galaxies, except their arms begin spiraling out from the straight line stars instead of from the center. i. Barred spiral galaxy 2. Elliptical Galaxies

7 About 1/3 of all galaxies Simply massive blobs of stars Round or elliptical in shape Contain very little gas or dust No new stars are forming because of little gas The largest and smallest galaxies are elliptical galaxies Do not contain nebulas 3. Irregular Galaxies Do not fit into any other category Chaotic mix of stars, gas, and dust Usually found near large spiral galaxies who may be distorting their shape CONTENTS OF GALAXIES Stars, planetary systems, gas clouds, and star clusters. Nebulae are giant clouds of gas and dust where stars may be formed (found in spiral galaxies, but not elliptical galaxies) Galaxy Clusters groups of galaxies that are bound together by gravity; made up of star clusters; star clusters are made up of stars bound together by gravity Stars star clusters galaxies galaxy clusters

8 Deep Sky Objects most of the objects that astronomers study are far beyond our own solar system including clusters of stars and several kinds of nebulae or clouds Extra vocabulary Nebula (plural is nebulae) is a cloud of dust and gas that exists in space, usually between stars Planetary nebula a relatively small, ball-shaped nebula that surrounds a star. The nebula forms from material ejected from the star s outer layers as the star begins to collapse. Diffuse nebula larger nebula with an irregular shape. Diffuse nebulae located near stars reflect starlight or give off their own bright light. Star cluster group of stars bound to each other by gravity. Star clusters can be classified into 2 general categories, galactic clusters and globular clusters. Galactic cluster an open cluster of stars that are loosely bound to each other by gravity Globular cluster spherical cluster of stars that

9 are tightly bound to each other by gravity Star life cycle video: LIGHT YEARS AND THE HR DIAGRAM Video on light years: LIGHT YEARS The distance that light will travel through a vacuum in a year Light can travel 7 times around Earth in 1 second SPEED OF LIGHT Light travels at 299,782,485 meters per second or 186,00 miles per second It takes 8 minutes for the light from the sun to reach the Earth. It would take 180 years to drive nonstop at 60 mph to go the same distance.

10 HERTZSPRUNG-RUSSELL DIAGRAM (HR DIAGRAM) Used to classify stars by Size how massive the star is Temperature A star s color reveals its temperature Red stars have a cooler temperature, and blue stars have a warmer temperature Brightness/Magnitude The amount of light a star gives off depends on the size and temperature BRIGHTNESS OR MAGNITUDE How bright a star looks fromm the Earth depends on both how far the star is from Earth and how bright the star actually is A star s brightness can be described in two ways: apparent magnitude and absolute magnitude APPARENT MAGNITUDE The brightness of a star as seen from the Earth ABSOLUTE MAGNITUDE The brightness of a star as if it were 32.6 light years from Earth The brightness of the stars is compared to the brightness of SUN. We call this LUMINOSITY.

11 HOW WE RECORD LIGHT WAVES CAN DETERMINE THE DIRECT OF STARS MOVEMENT HR DIAGRAM An HR diagram shows the most important characteristics of stars, which are temperature and absolute magnitude (brightness) and/or luminosity. Scientists plot the surface temperatures of stars and their brightness on a graph.

12 OLS UNIT 3 LESSON 1 The universe before the big bang was a densely packed space. If a star is moving away from the earth, its visible light will be shifting toward red. One fact used as evidence that the universe began with the big bang was leftover energy in the universe from the event. OLS UNIT 3 LESSON 2 The number of stars found in a galaxy are billions. An irregular galaxy does not have a distinctive shape. A barred spiral galaxy often looks like this The word elliptical refers to an oval. What best describes how galaxies exist in the universe is they form clusters that are light years away from each other. A light-year is the distance light travels in one earth year. A star that is 8 light years away will take 8 earth years to reach earth.