The Universe Chapter 20

The Life and Death of Stars Stars are huge spheres of hot gases that emit light and other forms of electromagnetic radiation. The distance between stars is measured in light years (the distance that light travels in one year). Star produce energy by nuclear fusion, fusing hydrogen in to helium.

Layers of a Star Core(15,000,000 K-site of nuclear fusion) Radiative Zone (2,500,000 K) Convective Zone (1,000,000 K) Photosphere(6000 K-layer that produces light) Chromosphere(4000-50,000K-layer that produces color) Corona(2,000,000 K-layer that produces ultraviolet rays)

Studying Stars Stars are classified by brightness. Absolute magnitude is the brightness of a star at a distance of 10 parsecs. Apparent magnitude is the brightness of a star as seen from the earth. Color of a star indicates the temperature of a star. Hotter stars are blue in color. Cooler stars are red in color. The spectral lines can indicate the composition of a star.

Fate of Stars The Hertzsprung-Russell diagram is a graph of all the stars in the Milky Way Galaxy. The temperature is on the x-axis. The luminosity or brightness is on the y-axis. Our sun is a main sequence star (typical).

Birth of a Star Stars are born from a cloud of gas or dust called a nebula. The cloud condenses to form a protostar. The protostar becomes a star when the core of the star reaches 15,000,000 K and nuclear fusion begins.

Star Life The more massive stars live for millions of years. The less massive stars live for billions of years. Through out the life of stars, elements are fused into larger elements (hydrogen to helium to carbon to oxygen to iron).

Life Cycle of Stars Stars that are less massive go from a main sequence star to a red giant and finishes as a dwarf star. Stars that are more massive go from a giant star to a supernova.

End of a Star’s Life Star that are less than 1.4 solar masses will use up all of its hydrogen and helium and become a white dwarf. Stars that are between 1.4-3.0 solar masses will produce a Type I supernova, leaving a neutron star. Stars that are greater than 3.0 solar masses produce a Type II supernova, collapsing and producing a black hole.

Galaxies A galaxy is a collection of millions or billions of stars. Galaxies are grouped in clusters. The Milky Way is a spiral galaxy (our galaxy). Types of Galaxies (by shape): Spiral galaxies (blue stars). Elliptical galaxies (red stars). Irregular galaxies.

Quasars Quasars are the most distant and most radiant objects in the universe (center of distant galaxies).

Origin of the Universe The universe is everything in space. The Big Bang Theory states that the universe began with a gigantic explosion 10 to 20 billion years ago. Proof of the theory is the red shift of stars showing the universe is expanding.

Future of the Universe The universe will keep expanding forever (Hubble). The expansion of the universe will gradually slow down, and the universe will approach a limit in size. The universe will stop expanding and start to fall back in on itself.

Tools to Study the Universe Reflecting telescopes use mirrors to magnify the image. Refracting telescopes use lenses to magnify the image. Radio telescopes collect radio waves to study the stars. Spectroscopes analyze the light given off by stars to indicate composition, movement and temperature of stars.

Reflecting Telescope

Refracting Telescope

Radio Telescope

Radio- refracting-reflecting Reflecting – refracting –radio One of the greatest advancements in astronomy was the telescope. Which is the correct order of advancements? Radio- refracting-reflecting Reflecting – refracting –radio Refracting-reflecting-radio Radio- reflecting-refracting 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Why do astronomers measure interstellar distances in light years instead of kilometers or miles? Light years are a measure of time. Miles and kilometers are too small of a unit. Miles and kilometers are too large of a unit. I don’t have a clue . . . help me! 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Which of the following correctly shows the age progression of an average star? Main sequence→White Dwarf→Red Giant →Nebula Red Giant →White Dwarf →Main Sequence →Nebula Nebula →Main Sequence →Red Giant →White Dwarf White Dwarf →Red Giant →Main Sequence →Nebula 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

What is the next likely stage of a protostar? Super Giants Nova Main Sequence Neutron Star 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

What type of galaxy is shown in the picture? Irregular Spiral Elliptical D. I have no idea … I need help!!! 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Review Questions Which unit is used to measure the distance between stars? light year Which type of telescope uses mirrors to see stars? reflecting telescope What happens to a star at the end of its life, that is more than 3 solar masses? supernova to a black hole

Review Questions What is the color of stars that are cooler? red What is the type of brightness of a star when it is observed from the earth? apparent brightness What is graphed on the x-axis of the H-R diagram? temperature

Review Questions What is graphed on the y-axis of the H-R diagram? brightness or magnitude How does a star produce energy? fusion How do we know that the universe is still expanding? red shift

Review Questions Name the three types of galaxies. irregular, spiral, elliptical What is used to classify galaxies? shape What is the color of very hot stars? blue Name the three types of telescopes. reflecting, refracting, radio

Review Questions How do you calculate the distance that light travels in one year? Multiply the number of seconds in a year by the speed of light. What is the speed of light? 300,000 km/s What is the name of the theory of the creation of the universe? Big Bang

Review Questions What do we call the most distance objects in the universe? quasars. How long ago did the Big Bang take place? 10 to 20 billion years ago What will the sun turn into when it dies? white dwarf

Review Questions Which galaxy do we live in? Milky Way What type of galaxy is the Milky Way? spiral Which type of galaxy has old red stars? elliptical Which type of galaxy has young blue stars?

Review Questions What can the spectrograph tell us about a star? compostion, temperature, and whether the star is approaching us or going away Who proposed that the universe is expanding by the red shift? Edwin Hubble What does hydrogen fuse into in a star? helium

Review Questions When does a star change from a nebula and protostar to a star? The core of the star heats up to 15 million K to begin nuclear fusion. What happens to a medium size star (1.4 to 3.0 solar masses) when it dies? supernova to a neutron star What do you call the brightness of a star at the distance of 10 parsecs? absolute magnitude

Review Questions What happens to a star from birth to death? nebula to proto star to either a white dwarf, supernova to neutron star or supernova to black hole How is the mass of the star related to the length of life of a star? low mass, long life; high mass, short life