Made of? Dr Risa H Wechsler Hubble Fellow" Enrico Fermi Fellow University of Chicago Lecture Plan Lecture Two" April #& The Story of Galaxy Formation in Our Universe: Kavli Inst for Cosmological Physics" Enrico Fermi Institute & Dept of Astronomy & Astrophysics Evidence for the Expanding Universe +/'01 made of? +TodaySeeds of Galaxy Formation and the Development of Structure +/'&$The Age" Shape and Expansion History of the Universe +%'2A Basic Picture of Galaxy Formation +%'0/Galaxy Interactions and the Hubble Sequence +%'#0Frontiers in Galaxy Formation +%'#3The Future of the Universe; Summary +1'/- Spring #$$% made of? Stars and The Elements http:''kicpuchicagoedu'(risa'compton' Arthur H Compton Lectures Made of? )baryonic* matter: made of protons & neutrons We are stardust Element Abundances H and He made a few minutes a.er the big bang Where did the rest come from? All heavier elements are formed in the cores and explosions of stars Main sequence +sun,like- stars: fusion occurs in the cores Abundances of various elements set by the temperatures of stellar cores and supernovae +and nuclear physics-
Escape velocity is the velocity required to escape a gravitational 4eld Larger for more massive things +vesc Earth ( 00k's; vesc Jupiter (1$ km'ssmaller for smaller distances +escape velocity from sun at earth radius ( /# km's" at pluto (2 km's- vorbit = Escape Velocity The concept of an escape velocity is relevant on various scales For a given mass and distance" there is a critical amount of kinetic energy +velocity- required to escape In the case of the big bang" given the initial amount of energy" there is a critical density of mass that is required to overcome this Above this mass" the Universe will contract under the weight of its own gravity +like the ball returning to earth-; below this it will expand forever +More on this in the next two lectures- Are the stars it? Adding up all the stars: we get ($%5 of the critical density With this small amount" gravity6s e7ect on the expansion would be very weak Stars form from the primordial gas" much of this gas must still exist Visible Matter: The Baryon Fraction Is what we can see all there is? Light does not necessarily trace mass The amount of mass in gravitationally bound objects can be determined by looking at their rotation velocities v= )Baryons*: matter made up from protons and neutrons Not all )baryonic* material is in stars Some remains in primordial gas +mostly hydrogen" both cold and hotthat has not yet formed stars BBN prediction is 2 Ωb = 0.019h 0.04 In good agreement with several other constraints Total baryon fraction predicted by BBN Still a very small fraction of the critical density in Galaxy Clusters Total )baryon* fraction The Coma Cluster
1937ApJ...86..217Z Fritz Zwicky measured velocities for (0$$$ galaxies in the Coma Cluster Expect v= Zwicky found +ApJ" 08&2-: More mass than light" by a large factor Spiral Galaxies in Spiral Galaxies 1937ApJ...86..217Z Galaxy Clusters Based on known stars in rotating disk galaxies" expect the rotation curves to fall o7 quickly Similar to planet rotation: stars on the outskirts should move more slowly Spiral Galaxies In mid 081$6s" Vera Rubin measured the rotation curve of the Andromeda galaxy It was close to 9at" not decreasing at large radii Subsequent measurements on other galaxies showed the same feature Indicates substantially more matter around galaxies than is seen in Spiral Galaxies Stability of Spiral Disks In 082&" Ostriker and Peebles did one of the 4rst gravitational )N,body* simulations Basic idea: N identical test particles" under the in9uence of a gravitational force Evolve and see what happens +Much more on this in next lecturethey found that a disk galaxy was unstable,, hard to keep it a disk for very long The addition of a spherical )halo* around the disk was able to stabilize the disk )The halo masses of our Galaxy and of other spiral galaxies exterior to the observed disks may be extremely large* Zwicky predicted that this additional mass should be observable by the de9ection of light around the galaxies'clusters Einstein6s General Relativity theory makes precise predictions for this de9ection Massive objects actually distort the spacetime Light passing through a strong gravitional 4eld follows the curved paths of this distorted space By measuring the de9ection" we can measure mass Illustration by Martin Kornmesser & Lars Lindberg Christensen, ST-ECF Illustration by Martin Kornmesser & Lars Lindberg Christensen, ST-ECF
a massive galaxy cluster Measuring the Total Mass of the Universe More mass : more gravity : slowing expansion rate" faster evolution of structure We will see in the next # lectures that the Evidence for Dark Matter What is? the total amount of mass amount of mass required for structure formation" and to explain the expansion rate +Hubble- is ;; /5 +at least (0'/ of the critical density- Abell 0138 Image with Hubble ACS Fast moving galaxies in clusters Flat rotation curves of spiral galaxies Stability of disk galaxies Baryon fraction +(/5- vs Total Mass in The expansion rate of the Universe depends on Universe +;#%5- Large,scale structure +next lecture
Doesn6t emit or absorb light in any wavelength Visible through gravitational e7ects What is? What is? Normal stu7 that doesn6t emit light? Brown Dwarfs or planets +)MACHOs*-" black holes" dark galaxies and clusters? Exotic particles +*non,baryonic*-? )Hot* : neutrinos? )Cold* : lightest super symetric partner particle? Incorrect law of gravity? Supersymmetry Two types of particles: bosons and fermions The Contents of Our Universe Particles decay" but only into lighter things Basic idea: each known particle has a supersymmetric partner particle" with almost idential properties" except that bosons +photons" quarks- have fermionic partners and fermions +electrons" neutrinos- have boson partners Supersymmetry is broken at very high energies +in the early universe-: supersymmetric particles are much more massive than their partners The lightest supersymmetric particle +neutralino" gravitino-will have nothing to decay into" so there will be a lot of them le.: the dark matter? further reading Next Time: How did structure form in our Universe? General: http://www.tufts.edu/as/wright_center/cosmic_evolution/ good introduction to the origin of the heavy elements WMAP Cosmology 0$0" on dark matter: http://map.gsfc.nasa.gov/m_uni/uni_101matter.html Alpha & Omega: The Search for the Beginning and End of the Universe Charles Seife +#$$&- see Chapter 1" The Dark Universe in the Universe" Vera Rubin Scienti4c American" December 0883 Supersymmetry" Gordon Kane +#$$$