Ch 30-Stars, Galaxies, and the Universe

1. Ch 30-Stars, Galaxies, and the Universe • Objectives • How astronomers determine the composition and temperature of stars • Why do stars appear to move in the sky • How astronomers measure the distance to stars • What is the difference between absolute magnitude and apparent magnitude • How a protostar becomes a star • How a main sequence star generates energy • The evolution of a star after its main sequence stage • Describe the characteristics that identify a constellation • The main types of galaxies • How a quasar differs from a typical galaxy • How did Hubble’s discoveries lead to an understanding that the universe is expanding • What is the Big Bang Theory • What is some evidence for the Big Bang Theory

2. Sec 1-Characteristics of Stars • Star-a ball of gases that gives off a tremendous amount of electromagnetic energy • Where does this energy come from? • Nuclear fusion-combination of light atomic nuclei to form heavier atomic nuclei • Vary in color • Analyzing Starlight • Astronomers analyze starlight by using spectrograph. Starlight produces spectrum-display of colors and lines • Emission, absorption, continuous • By studying spectrum, scientists can determine star’s composition, temperature, and elements that make up the star

3. Composition and Temperature of Stars • Every chemical element has characteristic spectrum in given range of temps • Colors and lines in the spectrum of star indicate elements that make up the star • Same elements of Earth • What is most common element of Earth? • What is most common element of a star? • Surface temp of star is indicated by star’s color • Temps of stars range from 2800-24,000.

4. Classification of Stars

5. Stellar Motion • Apparent Motion of Stars-motion visible to the unaided eye. Caused by the movement of the Earth • Circular trails makes stars seem to move in circular pattern-caused by rotation of Earth • Different stars become visible during different seasons. Why? • Circumpolar Stars-stars that are always visible in night sky • Movement of stars makes them appear to circle Polaris • Little Dipper

6. Actual Motion of Stars • Several types of movement • Rotate on axis, revolve around another star, either move away from or toward our solar system • Can learn a lot from star’s spectrum • Spectrum of star moving toward or away from Earth appears to shift • Doppler effect-observed change in the frequency of a wave when the source or observer is moving • Shift appears to move toward Earth=Blue shift, shorter wavelengths • Shift appears to move away from Earth=Red shift, longer wavelengths

7. Distance to Stars • What is a light yr? How fast does light travel? • How far does light travel in one yr? • How can scientists measure the distance of relatively close stars? • By measuring the parallax-the apparent shift in the position of an object when viewed from different locations • Use this method for any star w/in 1,000 light yrs of Earth

8. Stellar Brightness • More than 3 billion stars can be seen through telescope on Earth • Only bout 6,000 are visible w/out telescope • Visibility of star-brightness and distance from Earth • Apparent magnitude-brightness of star as seen from the Earth • Absolute magnitude-brightness that a star would have at a distance of 32.6 light yrs from Earth • Brighter the star=lower number of absolute magnitude

9. Sec 2-Stellar Evolution • Scientists use the Hertzsprung-Russell diagram to classify stars based on their luminosity and surface temps • Luminosity-total amt of energy they give off each second • Star formation • Begins in nebula-cloud of gas and dust. Consists of 70% hydrogen, 28% helium, 2% heavier elements • Explosion of nearby star compresses cloud, particles move closer together by gravity

10. Star formation cont. • Objects increase in mass, gravity also increases, causes nearby particles to be pulled into increasing mass. Dense matter begins to build up • Shrinking, spinning region begins to flatten into disk-has central concentration of matter called protostar • Gravitational energy converted into heat energy-causes temp of protostar to increase • Continues increasing in temp for several million yrs • Gas becomes very hot, nuclei and free electrons move independently-gas now considered plasma • Continues increasing to about 10,000,000 deg C, nuclear fusion begins-marks the birth of star • Fusion of Hydrogen to Helium

12. Main-Sequence Stage • 2nd and longest stage in life of star • Energy generated in core of star-hydrogen fuses into helium-enormous amts of energy • Star with mass of our sun stays in main sequence for 10 billion yrs • Some may spend more time in main sequence or some may fuse hydrogen so rapidly it only stays in main sequence for 10 million yrs • Scientists estimate that the sun has only converted 5% of hydrogen into helium in the last 5 billion yrs, another 5 billion yrs, 10% of sun’s original hydrogen converted, fusion will stop in core • What happens when fusion stops? • Sun’s temperature and luminosity will change and sun will move off the main sequence

13. Leaving Main Sequence • Enters 3rd stage when almost all of hydrogen atoms w/in core have fused into helium atoms • Star contracts under own gravity, core becomes hotter, energy transferred to outside hydrogen shell. Fusion continues in outer shell and shell expands • Giants-very large and bright star whose hot core has used most of its hydrogen-takes place when star’s shell expands and becomes cooler • Supergiants-highly luminous stars that become larger and more massive than giants

14. Final Stages of Sunlike Star • Fusion stops-star’s outer gases drift away, gases appear as planetary nebula-cloud of gas that forms around sunlike star that is dying • Planetary nebula disperses, gravity causes remaining matter in the star to collapse inward. White dwarfs-small, hot, dim star that is the leftover center of an old star • Black dwarf-white dwarf that no longer gives off light

15. Nova-star that suddenly becomes brighter • White dwarf revolves around red giant, it captures gases, pressure builds up, pressure may cause large explosions-release energy and stellar material into space • Supernova-star that has tremendous explosion and blows itself up • Thousands of times more violent than novas • Destroy white dwarf star and red giant • http://glencoe.com/sec/science/earthscience/2007/concept_motion/animated_art/StarFormation29_18.swf

16. Final Stages of Massive Stars • 8 times the mass of the sun • Massive stars become supernovas as part of life cycle • Supernovas in massive stars-after supergiant stage, stars contract w/ gravitational force much greater than small-mass stars • Collapse produces high pressure and temps, nuclear fusion begins, carbon atoms fuse into heavier elements • Fusion continues until core it made up entirely of iron, takes energy rather than giving off, uses up supply of fuel and gravity causes core to collapse, explodes w/ tremendous force • Puts out more energy than a sunlike star does in its entire lifetime

17. Neutron Stars-star that has collapsed under gravity to the pt that the electrons and protons have smashed together to form a dense ball of neutrons • Forms after star explodes as supernova • Rotates very rapidly • Pulsars-rapidly spinning neutron star that emits pulses of radio and optical energy • Black hole-object so massive and dense that even light cannot escape its gravity • If star contains 3 times the mass of the sun, may contract under its greater gravity, the force crushes the dense core of star, leaves black hole • How do scientists locate black holes?

18. Sec. 3-Star Groups • Constellations-group of stars organized in a recognizable pattern • One of 88 regions into which the sky has been divided in order to describe the locations of celestial objects • Are stars that make up a constellation all the same distance from Earth?

19. Galaxies • Galaxy-large scale group of stars, gas, and dust that is bound together by gravity • Major building blocks of the universe • Milky Way has diameter of 100,000 light yrs, 200 billion stars • Types of Galaxies-classified by shape • Spiral galaxy-large with a nucleus of bright stars and flattened arms that spiral around the nucleus • Elliptical galaxies-vary in shape from nearly spherical to very elongated. Similar to stretched out football field • Irregular galaxy-no particular shape, usually low total mass and fairly rich in dust and gas

20. Milky Way • Spiral galaxy in which the sun is one of billions of stars • Each star orbits around the center of Milky Way galaxy • Large Magellanic Cloud and Small Magellanic Cloud-irregular galaxies and 170,000 light yrsaway • http://glencoe.com/sec/science/earthscience/2007/concept_motion/NGS/Visualizing_The_Local_Group_30.swf

21. Quasars Taken with Hubble space telescope • Quasar-quasi-stellar radio source; a very luminous object that produces energy at a high rate • Not related to stars, but related to galaxies • Project a jet of gas • Are located in centers of galaxies-distant from Earth • Among most distant objects that have been observed from Earth

22. Nebular Hypothesis • Solar system-sun and all of the planets and other bodies that travel around it • What is a planet? • Celestial body that orbits the sun, is round cause of its own gravity, and has cleared neighborhood around its orbital path • Nebular hypothesis-states that the sun and planets condensed at about the same time out of rotating cloud of gas and dust-nebula • Scientific calculations support hypothesis • Solar nebula-rotating cloud of gas and dust from which the sun and planets formed • About 99% of all matter contained in solar nebula now exists in sun

23. Formation of Planets • Planetesimal-small body from which planet originated in early stages of development of solar system • Protoplanets-larger bodies that were formed through collisions and through force of gravity • Moons-smaller bodies that orbit planets • Planets and moons are smaller and denser than protoplanets

24. Sec 4-The Big Bang Theory • Cosmology-study of the origin, structure, and future of the universe • Edwin Hubble-astronomer who made very time consuming observations that uncovered new information about our universe • Found spectrum of galaxies by using light given off by entire galaxy • By using spectra, Hubble was able to tell that the galaxies were shifted to the red end of the spectrum • By examining the amount of red shift, he determined the speed the galaxies were moving from Earth • By using Hubble’s observations, astronomers were able to determine that universe is expanding

25. Big Bang Theory Emerges • The theory that all matter and energy in the universe was compressed into a extremely small volume that 13 to 15 billion yrs ago exploded and began expanding in all directions • Current and most widely accepted theory on origin of universe-cosmologists • As universe expanded-some of matter gathered into clumps that evolved into galaxies • Expansion of universe into space explains the red shift detected in spectra of galaxies • Theory accepted by almost all astronomers

26. Cosmic Background Radiation • Radiation uniformly detected from every direction in space; considered a remnant of the big bang • Formed shortly after the big bang • Shortly after big bang, universe would have been very hot and cooled to great extent by now • Temp of radiation is 270 deg C below zero

27. Ripples in Space • Ripples are irregularities in cosmic background radiation-caused by small fluctuations in the distribution of matter in the early universe • Ripples may indicate the 1st stages in the formation of the universe’s first galaxies • On a map that shows temps that differ from the average background temp ripples become apparent

28. Universe of Surprise • Astronomers think the universe is made up of more mass and energy than what can be detected • Dark matter-type of matter which does not give off light and has gravity we can detect • Dark energy-unknown material that scientists think acts as a force that opposes gravity • Pushing galaxies apart and increasing the rate of expansion