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. “the Great Wall” Earth Virgo Cluster Expanding Universe Today’s Lecture: purpose & goals Looking at an ‘empty patch of sky AST 1002 Planets, Stars and Galaxies 1)Hubble’s Law 2)Expanding Universe 3)Cosmology Assumptions 4)The Origin of the Universe “the Big Bang” 5)Fate of the Universe

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

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

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” 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. Andromeda galaxy size of the Moon

8. Calculate the distance to the Andromeda Galaxy using Hubble’s method. m - M v = -5 + 5log 10 (d (parsecs) ) Luminosity-Period Relation of Cepheid Variables Andromeda galaxy Distance Modulus Formula

9. 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.) rest - = observed Z 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 = H 0 x d What is H 0 ? Hubble’s data distance to galaxy Recessional velocity

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 First detailed study done by Margaret Geller & John Hucra, Harvard-Smithsonian Center for Astrophysics “the Great Wall”

12. Hubble’s Law Holds for essentially all galaxies with measured redshift 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 H 0 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. 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 rest - = observed Z 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 years back 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 = H 0 x d  d = v/H 0 But distance = rate x time (the time here is how long the expansion has been going on  The Age of the Universe)  t hubble = 1/H 0

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. 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. Cosmic Microwave Background (CMB)

23. Composition of Light Elements Helium Big Bang model predicts the percentage of light elements Hydrogen ( 1 H), deuterium (heavy hydrogen, 2 H), helium ( 4 He), lithium ( 7 Li), beryllium ( 9 Be), boron ( 10 B and 11 B),… 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 ( 1 H) and helium ( 4 He), with only trace amounts of anything else.  must have cooled from something very hot.

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 H 0 = 70 km/(s Mpc), critical mass density is 8x10 -27 kg/m 3 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 matter in galaxies (measured by galaxy rotation curves) about 10 times as much;  MASS = 0.2 Dark matter between 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? Answer: Strangely enough… the rate of expansion is speeding up! 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!!)

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