final exam!!!

1. final exam!!! • Today we will discuss Cosmology and the Big Bang • Wednesday we will finish the Big Bang, have a short discussion of Life in the Universe, and review for the final exam • Remember:

2. AST 1002 Planets, Stars and Galaxies Expanding Universe “the Great Wall” Today’s Lecture:purpose & goals Hubble’s Law Expanding Universe Cosmology Assumptions The Origin of the Universe “the Big Bang” Fate of the Universe Virgo Cluster Earth Looking at an ‘empty patch of sky

3. Galactic Clusters – II • SuperClusters • On even greater scales the galaxy clusters themselves form clusters called superclustersthat can be tens to hundreds of millions of light years across. • These superclusters resemble “…the froth on soap bubbles…” in space. • Between them lie great voids containing relatively few galaxies. Virgo III group 10 million ly Virgo Cluster Local Group Canes group Sculptor Ursa Major group Leo I Leo II group Fornax Cluster

4. Galaxy Collisions • Occasionally galaxies collide • Happens most often in centers of rich galactic clusters • Stars that make up the galaxies don’t actually slam into each other • Passage of one galaxy through/near another causes major “stirring” • due to gravitational interaction • Causes new activity such as • huge burst of star formation, • creation of AGNs,… Think of walking around before or after a football game

5. Review slow rotation very little gas and dust Pop II no new star formation!! fast rotation Pop II Pop I significant gas and dust– in arms significant new star formation!! (in the spiral arms, spherical component older!!) small, irregular, no rotation some gas and dust some new star formation (randomly throughout galaxy)

6. Measuring Distances • Stereoscopic viewing (Parallax) • only “small” distances • nearest few thousand stars in our galaxy • “Standard candles” • objects which have ‘known’ luminosities • Cepheid variables • variation tells luminosity – good to 65-100 million LY • brightest stars in galaxy, size of HII regions, overall brightness of galaxy – good in steps out to 1-2 billion LY • Type Ia supernova • all have same luminosity • good to 8-10 billion LY (a few measured as far away as 12-13 billion LY) • Relies on Comparison to examples of the same type objects in nearby galaxies

7. History reminder– “Island Universes” Andromeda galaxy • 1924 – Edwin Hubble • Measured the distances to several galaxies using the Luminosity-Period relationship of Cepheid variables, discovered by Henrietta Leavitt (1912). (Cepheid variables) • This was conclusive proof that the galaxy lay well beyond the Milky Way.  2 million l.y. away! • The universe was much larger than previously thought. size of the Moon

8. Andromeda galaxy Distance Modulus Formula • Calculate the distance to the Andromeda Galaxy using Hubble’s method. • m - Mv = -5 + 5log10(d(parsecs)) Luminosity-Period Relation of Cepheid Variables

9. l - l observed rest Z = l rest Galactic Redshifts • Edwin Hubble (1889-1953) and colleagues • measured the spectra (light) of many galaxies • found nearly all galaxies are red-shifted • Redshift (Z) • From Ch. 2, (Doppler effect)Z = v/c (for speeds approaching c, we’ll need a relativistic version of this equation.) Andromeda galaxy Z = [(1+ v/c)/(1+ v/c)]1/2 - 1

10. Hubble’s Law • Hubble found the amount of redshift depended upon the distance • the farther away, the greater the redshift v = H0x d Recessionalvelocity What is H0? Hubble’s data distance to galaxy

11. Bigger Structure • Structure bigger than galaxies • Galaxy groups • 2-30 galaxies • Local Group – contains the Milky Way • Galaxy clusters • 100s of galaxies – Virgo Cluster (rich cluster) • Superclusters • groups and clusters combined • The Universe is filled with large scale structure • “walls” and “filaments” separated by great voids – (like froth on soap bubbles) Earth Virgo Cluster “the Great Wall” First detailed study done by Margaret Geller & John Hucra, Harvard-Smithsonian Center for Astrophysics

12. Hubble’s Law • Holds for essentially all galaxies with measuredredshift and distance • THEREFORE, measuring the redshift tells us the distance • redshifts up to 95% of the speed of light have been measured!! • ultraviolet wavelengths can be shifted into the visible, or infrared • H0 is Hubble’s constant = 70 km/(s Mpc) • Mpc = megaparsec

13. Consequences • If everything is moving away from us and things farther are moving faster • Then the Universe is expanding! This doesn’t mean what you are probably thinking . . . .

14. Expanding Universe • Space itself is expanding, not matter flying apart within space. • Examples: • dots • rubber band • raisin bread • ants on a balloon • It does not mean we are at the center of the Universe • every part of the Universe sees everything moving away from it

15. l - l observed rest Z = l rest Cosmological Redshift • We now know 3 kinds of redshift • Doppler shift • due to motion • Gravitational shift • due to distortion of space-time by mass • Cosmological shift • due to stretching of space • not due to relative motion • as space stretches, the wavelength stretches and becomes longer Relativistic (near speed of light): Z = [(1+ v/c)/(1+ v/c)]1/2 - 1 Non-relativistic (<0.05c): Z = v/c

16. Looking Back in Time • Remember it takes time for light to reach us • travels at 300,000 km/s • So we see things “as they were” some time ago • The farther away, the further back in time we are looking • 1 billion LY means looking 1 billion yearsback in time • So the greater the redshift, the further back in time • redshift of 0.1 is 1.4 billion lightyears which means we are looking 1.4 billion years into the past

17. Thinking Back in Time • If all galaxies are moving away from each, then in the past all galaxies were closer to each other. • Going all the way back, it would mean that everything started out at the same point • then began expanding • This starting point is called the Big Bang • We can calculate the age of the Universe using Hubble’s Law v = H0x d  d = v/H0  thubble=1/H0 But distance = rate x time (the time here is how long the expansion has been going on  TheAge of the Universe)

18. Big Bang • At the beginning of our Universe, all matter was together in a very compact form • matter was nothing like it is now • very “hot” • Then space started expanding • things “cooled” • eventually it was possible for normal matter to “condense” out of the hooter form • Big Bang model makes a number of testable predictions….

19. …continued!

20. At the Beginning • Originally all the energy (and matter) of the Universe was condensed into an incredibly small region • MUCH smaller than the size of a proton • Energy, matter, space and time were all very different than today • need a new “theory of everything” to understand • not yet possible • 11-dimensional space??? (models are very weird) • During early expansion, space-time and gravity became separate from energy and mass • particles and antiparticles were being created from energy and annihilating into energy all the time

21. Glow of the Universe • The early Universe was very hot and dense • glowed with blackbody radiation • but so dense the light kept getting absorbed (opaque) • Eventually the Universe cooled enough to form hydrogen atoms • blackbody radiation could now travel freely • That time called “recombination of the Universe” • Light from that time should be all around us and be detectable. • 3K background radiation

22. Cosmic Microwave Background (CMB) • This light should be cosmologically redshifted • Mostly into microwave region • CMB was first seen in 1960s • Pensias & Wilson (Bell Labs) – won Nobel prize in physics for this • twenty years after prediction • COBE satellite mapped the CMB • measured the spectrum • wonderful match between theory and data  Temperature = 2.73K • cooled glow from recombination era. • Incredibly uniform across sky.

23. Composition of Light Elements • Big Bang model predicts the percentage of light elements • Hydrogen (1H), deuterium (heavy hydrogen, 2H), helium (4He), lithium (7Li), beryllium (9Be), boron (10B and 11B),… • elements formed before recombination (created out of light!) • percentages depend upon density and temperature of early Universe, and how fast it cooled. • Observed percentages agree with Big Bang model predictions • Almost all was created as hydrogen (1H) and helium (4He), with only trace amounts of anything else.  must have cooled from something very hot. Helium

24. Fate of the Universe • The Universe is expanding • But gravity should be pulling it back in • So what should the Universe’s fate be: • Continue expanding forever • Have expansion keep getting slower forever and stop at infinite time • Expansion stops and eventually Universe collapses upon itself • These possibilities are called • open universe • flat universe • closed universe

25. Enough Matter? • The amount of matter in the Universe helps determine its fate • if there is enough mass, gravity wins • given H0 = 70 km/(s Mpc), critical mass density is 8x10-27 kg/m3 • define MASS as the actual density of mass in the Universe divided by the critical density • MASS < 1 is an open universe • MASS = 1 is a flat universe • MASS > 1 is a closed universe

26. Enough Matter? • Visible matter (stars in galaxies, & hot gas) • only 2% of critical density; MASS = 0.02 • Dark matterin galaxies • (measured by galaxy rotation curves) • about 10 times as much; MASS = 0.2 • Dark matterbetween galaxies • (measured by watching galaxies fall inward in galactic clusters and from gravitational lensing) • raises total to 30% of critical density • MASS = 0.3 • We do not observe enough matter to cause the Universe to be closed • But it’s not the end of the story…

27. Is the Expansion Slowing Down? • Use Type 1a supernovae • a standard candle • use brightness to determine distance • use redshift to determine speed • compare them • data lies below prediction (galaxies are speeding up!!) • Answer: Strangely enough… the rate of expansion is speeding up!

28. Formation of Structure • (early in the Universe) • Normal matter was spread fairly evenly • due to interactions and radiation • Dark matter was not distributed smoothly • clumps remained • Expansion spread things out • but gravity held large clumps of dark matter together • Dark matter attracted normal matter • source of galaxies and structure