1. Radar Ranging 2. Triangulation idea

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1 Chapter 34: Cosmology Cosmology: How The Universe Works Cosmology is the study of the structure and evolution of the universe. To understand the universe we need to be able to tell Where things are Where things are moving How does the universe work? What do we know of how thing are, were, and are to be? Don t t have all the answers but some evidence is accumulating PS 110A-Hatch-Ch PS 110A-Hatch-Ch FYI How do we measure distances, to stars and galaxies, etc.? There are about billion stars in our galaxy! There are about billion galaxies in our universe! We see about 10,000 stars with the naked eye in the desert --some are galaxies. Milky Way is about 100,000 light years across PS 110A-Hatch-Ch R.R. 1. Radar ranging 2. Triangulation 3. Brightness - distance 4. Doppler shift T. B.-D. D.S. relatively short scale of distances relatively long PS 110A-Hatch-Ch Radar Ranging 2. Triangulation idea B Set up similar triangles angles are the same. Distance = (speed of light) x (time) x 1/2 Applicability? Only to earth s nearest neighbors -- moon, sun, solar system PS 110A-Hatch-Ch θ b x 3 θ 5 a 4 meters c A 120 meters C P1: If you have similarity and know one side. x =? PS 110A-Hatch-Ch

2 Triangulation of Star Positions θ 1 θ 2 Know θ 1, θ 2, length Applicability 1. Use on ~10,000 stars in the near neighborhood (100 light years) of the sun (just part of our galaxy) 2. Requires a telescope for such small angle differences. (First done in the mid 1800s). 3. Brightness Three quantities are related: But we want to see even farther! 1. Absolute brightness 2. Apparent brightness 3. Distance to the star (unknown) If you knew first two,, you could calculate the third. (100 watt bulb) PS 110A-Hatch-Ch PS 110A-Hatch-Ch Herzsprung and Russell knew that Harlow Shapley was able to point out that we are not at the center of the galaxy a. Stars vary in temperature and that means in color blue-hot and bright white - not quite so hot and bright yellow- so-so red- cool b. The color can be measured from the earth. H. &. R. assumed that from color of the star they could get the absolute brightness. Then with apparent brightness calculate the distance They check their method for stars close enough to get distances b triangulation. It worked PS 110A-Hatch-Ch Harlow Shapley He found the position by measuring distances to the globular star clusters that orbited about the center of the Milky Way. (early 1900 s) Globular Cluster PS 110A-Hatch-Ch Position of the Sun in the Milky Way The sun is 2/3 the way from the galaxy center to the edge. Its position was found by measuring distances to the globular star The Sun clusters that orbited about the center of the Milky Way. Variable stars were used to find the distances. Globular Clusters x x PS 110A-Hatch-Ch Variable Stars as Distance Indicators A class of very bright stars called Cepheids, have a tight relation between their real brightness and their pulsation periods. Pulsation period real brightness measured brightness distance The primary mission of the Hubble Space Telescope was to find distances to nearby galaxies using Cepheid variable stars. 15 days 45 days 30 days * ** 10 days PS 110A-Hatch-Ch

3 External Galaxies Our Galaxy is not unique It wasn t until 1923 that we fully realized the universe consisted of more than the Milky Way. Using Cepheid variable stars, Edwin Hubble determined that the Andromeda galaxy was a separate system of stars. Soon it was realized that all spiral-shaped nebula were galaxies of stars similar to the Milky Way. On average over 100 billion stars per galaxy! Huge! The universe itself is only 10 5 time larger than a typical galaxy. At least 50 billion of Sketch of a galaxy: William Parsons, 1845 Edwin Hubble with his 200 inch telescope Andromeda galaxy is 200 million light them. years away PS 110A-Hatch-Ch HST photo of the galaxy PS 110A-Hatch-Ch The Hubble Deep Field Looks back 13 billion years, at 10,000 galaxies. PS 110A-Hatch-Ch PS 110A-Hatch-Ch Elliptical Galaxies Spiral Galaxies PS 110A-Hatch-Ch PS 110A-Hatch-Ch

4 Barred Spirals Irregular/Peculiar PS 110A-Hatch-Ch PS 110A-Hatch-Ch Galaxy Clusters Galaxies are held together in small to large groups by gravity. 4. Cosmological Redshift and The Doppler Effect A profound discovery of the early 1900s was that all distant galaxies have their absorption and emission spectral lines shifted to the red. the amount of the shift is related to the speed of the galaxy. Demo: bell tower recording PS 110A-Hatch-Ch PS 110A-Hatch-Ch Measuring Motion Doppler Spectroscopy The Doppler effect causes waves to shift up in frequency as they move towards you and down in frequency as they move away Light examples Doppler broadened laser cosmological redshift Video: train pitch Demo: swinging sound source, web animation, ripple tank PS 110A-Hatch-Ch shifted toward the red Discrete Spectrum from hydrogen atoms in the laboratory lower frequency discrete spectrum from hydrogen atoms moving with a star or galaxy away from the viewer Red Shift faster moving stars are farther away, more shift PS 110A-Hatch-Ch

5 Cosmological Redshift Spectral emission (absorption) lines have a characteristic pattern The pattern is shifted to the red for distant stars The amount of shift related to the speed of the star Galaxies far away P2: A galaxy that is six million light years away 1) is six million years old right now 2) appears to us as it looked six million years ago 3) was six million years old when the light left it 4) is within our own galaxy PS 110A-Hatch-Ch PS 110A-Hatch-Ch Distances The Hubble Law is used to find distances to the farthest galaxies Hubble Law (~1925) The speed a galaxy 55 million ly moves away from us is proportional to its distance. The farther away the galaxy is, the faster it recedes. This could mean we are at the center of the universe but not likely. 200 million ly PS 110A-Hatch-Ch PS 110A-Hatch-Ch Expansion Distance Measurements Summary If the universe is expanding, the farther away two galaxies are, the faster they move apart. Also, all galaxies would appear to be moving away from all other galaxies so our view is not unique. Video: 4 galaxies on balloon radar ranging triangulation distance-brightness cosmological redshift within solar system nearest 10,000 stars in galaxy within our galaxy and nearby galaxies beyond nearby galaxies PS 110A-Hatch-Ch PS 110A-Hatch-Ch

6 Types of Cosmologies Early ideas of the universe (steady state) held that it was: Infinitely old Infinitely large Unchanging in time But this cannot be true because The universe is seen to be expanding and thus it is changing with time. An infinitely large and infinitely old universe would never know darkness. This is Olber s paradox PS 110A-Hatch-Ch Why is Night Sky Dark? Olber Earth All lines of sight end on a star! The sky should be ablaze with star light! The solution is that the universe has a beginning Light has not had time to reach us from the greatest distances Glowing stars and galaxies have not always existed. PS 110A-Hatch-Ch Basic Ideas Each galaxy started by condensation of huge clouds of hydrogen gas. Particularly dense regions compressed by gravity to for stars. Currently our universe is dominated by fusion of hydrogen to form helium. Structure is stable now, but what happens when hydrogen is used up Big-Bang Bang Theory the universe began with an incredibly dense concentration of mass energy in the process of rapid expansion and cooling matter was formed point-like particles (electrons, quarks, photons, etc.) nucleons (protons and neutrons) simple nuclei (hydrogen and helium) more complex nuclei, atoms, and molecules Age of the universe is ~ 14 billion years old The fate of the universe depends on its mass and energy Open, it keeps expanding forever Closed, it collapses back in on itself PS 110A-Hatch-Ch PS 110A-Hatch-Ch What observations must a good model of the universe explain? *1. The expanding universe. (the red shift) 2. The age of the universe. *3. The abundance of hydrogen (75%), helium (24%), and other elements. (process of particle formation) *4. The microwave radiation (3K). (even in black space, started with the big bang) 5. The structure of observed matter. The model called the Big Bang does quite well and is now widely accepted by scientists the Steps in Big-Bang Bang Theory Time Temp Structure sec huge??? sec deg quarks, gluons, electrons, neutrinos, photons.001 sec deg protons and neutrons 3 minutes 10 9 deg 1/2 hour 10 8 deg 3 H, 3 He, 4 He nuclei 2 H nucleus 500,000 yrs deg atoms modern science creation view. PS 110A-Hatch-Ch PS 110A-Hatch-Ch

7 Experimental Evidence cosmological red shift Everything is moving away from us helium/hydrogen ratio (25%/75%) Fusion early after the big bang would produce that ratio of H to He (~ 3 min.) Big Bang Stellar Fusion Experimental Evidence universal microwave radiation (3K) Expect low frequency leftover energy from an explosion of that magnitude Supernova PS 110A-Hatch-Ch Wavelength (mm) PS 110A-Hatch-Ch Evidence Supporting the Big Bang Arno Penzias and Robert Wilson Nobel Prize, 1978 We see the expansion We see a faint glow left from the original fireball. Called the Cosmic Microwave Background or 3 K Background Radiation. What does the big bang predict for the future of the universe? It depends: IF the universe is open...the galaxies will separate forever. Space time will expand forever. Fewer suns will be formed and finally the stars will all burn out. IF the universe is closed...the universe will cool and the galaxies will slow down then collapse. a Big Collapse or Big Crunch What makes the difference? Mass don t t forget dark matter (not emitting light). Are there bounds to the heavens? PS 110A-Hatch-Ch PS 110A-Hatch-Ch Expansion reverses - closed Now Expansion Stops - flat Now Size of Universe Closed Size of Universe Flat Closed Big Bang Time Big Crunch? PS 110A-Hatch-Ch Big Bang Time Big Crunch? PS 110A-Hatch-Ch

8 Expansion Continues - open Supernova Explosion 1987 IA Now Open Size of Universe Flat Closed Before During Big Bang Time Big Crunch? PS 110A-Hatch-Ch PS 110A-Hatch-Ch Type IA Supernova The Ultimate Fate of the Universe Gravity always pulls, never pushes. So the expansion should slow down. Spectrum and brightness are perfectly correlated (days to brightest portion, months to die out) ----unless Einstein is correct and there is a cosmological constant force expanding space. Gravity fights at first but loses out in the end. Associated with dark energy (matter) Video: spectrum as function of (fast) time PS 110A-Hatch-Ch PS 110A-Hatch-Ch Which model (flat, open, etc.) is correct? By looking in the past we can compare the shape of the universe expansion curves. We use supernovae explosions to check brightness, distance, and velocities. At most one star per galaxy per decade. During the last ten years we find that none of these is correct. The universe expansion is speeding up faster than all these predict. Accelerating expansion Video:Type IA supernova explosion. 25% dimmer than the open growth predicts. Video:expansion for runaway growth. PS 110A-Hatch-Ch PS 110A-Hatch-Ch

9 The Ultimate Fate of the Universe Question Not enough mass - open universe Just right - flat universe Too much mass - closed universe (bang-bangbang?) Another force - runaway universe. This is what we think is happening! PS 110A-Hatch-Ch P3: Of the methods described for determining distances, the one which is limited to measuring distances within our solar system is: a. brightness-distance relationships b. radar ranging c. triangulation d. Doppler spectroscopy PS 110A-Hatch-Ch Question P5:Forces slowing the expansion of the universe are due to P4: Consider light observed on earth that was emitted by atoms moving with stars or galaxies. Which statements are true? a. You can actually see little red atoms that have been shifted to the left. They have small beady red eyes and cannot be trusted. b. The spectral colors emitted by the atoms moving with most of those objects are shifted toward higher frequencies. The shift is greater for objects that are farther away. This red shift is the basic evidence for the belief that the universe is expanding. c. none of the above a) The cosmological interaction b) The nuclear interaction c) The electromagnetic interaction d) The gravitational interaction PS 110A-Hatch-Ch PS 110A-Hatch-Ch