1. SMDEP Physics Today: Astronomy, Extrasolar Planets, Cosmology, Dark Matter, Dark Energy, Black Holes and more http://www.astro.yale.edu/krines/smdep New address: http://www.cfa.harvard.edu/~krines/smdep/

2. Test Results Mean = 20.3/37 (max:33) Median = 20 Stddev = 5.5 CLASS PARTICIPATION AND HW Homework: 36 possible, mean: 26, max:34 Bonus HW: 22 possible, mean: 16, max:22 Group revotes: 36 possible, mean: 20, max: 30 Total of above: 94 possible, mean: 62, max: 81

3. Next Year KR moving to Boston –New email: krines@cfa.harvard.edu –SMDEP Physics webpage to end (move?) Full-time research, so please email for help with physics courses Open invite: –If you’re in Boston, I’ll take you out to lunch –Email ahead of time

4. Blackbody Radiation Photons emitted by object at temperature T –Characteristic shape: more photons as frequency increases until peak, then fewer with high- frequency tail –Peak wavelength: T = 3 x 10 -3 m K Examples: –Sun: T=6000 K, peak at  = 450 nm -> optical –Light bulb: T=2200 K, peak at  = 1.4 x 10 -6 m (IR) –People: T=300 K, peak at  = 10 x 10 -6 m (IR) –Echo of Big Bang: T=3K, peak at  = 1 mm (microwave)

5. Blackbody Radiation

7. The Sun Why does the Sun shine? –Late 19 th century: as ball of gas contracts, gas releases potential energy as radiation Timescale of 10 million years –Must be other source of energy Nuclear fusion: ‘Burn’ hydrogen into helium E=mc2 Timescale of: (total energy available)/(Power) –Total energy available is 10% of Sun’s mass, converted at 0.008% efficiency –Power is light output by Sun –Timescale of 10 billion years

8. Pioneer 10 and Pioneer 11 were launched in the 1970s to explore planets in the outer solar system. They transmit radio signals back to Earth at a specific frequency. To hear these signals, scientists on Earth tune their radio dishes to: 1.The same frequency transmitted by Pioneer 10 2.A higher frequency 3.A lower frequency

9. Aliens on a planet orbiting a nearby star send a laser signal out to space at a specific wavelength. If astronomers could detect this laser over an entire orbit and plotted wavelength versus time, they would see: 1.A constant wavelength 2.A continuously increasing wavelength 3.A continuously decreasing wavelength 4.A sine wave

10. Extrasolar Planets Key concepts: Gravity, Orbits, Center of Mass, Circular Motion as Simple Harmonic Motion, Light as Wave, Doppler effect –Star much much brighter than planet Also, diffraction limit –Both planet and star orbit center of mass of system –Monitor velocity of star by watching spectral lines from atoms Lines show Doppler shifts Circular motion looks like oscillation -> sine wave!

11. Extrasolar Planets

13. A Quick History of the Universe Big Bang: space is infinitely dense, infinitely hot –Known laws of physics break down After Big Bang, space expands, Universe cools –At some temperature, protons and neutrons form –A little later, the protons and neutrons make Helium (most Helium in the universe was formed in the first 3 minutes after the Big Bang) –Nuclei, electrons, and photons in big “soup” Nuclei try to collapse (gravity), photons push back (pressure) This leads to OSCILLATIONS! Size of oscillations measures geometry of universe (know physical size, angle, so can measure geometry) –“Soup” cools, atoms form, and photons escape with nearly uniform temperature These photons get stretched by space, become microwaves

16. Expansion of Universe: Hubble’s Law Is universe static or dynamic? –If static (and eternal), very small fluctuations would grow via gravity -> not static –Einstein suggests “cosmological constant” keeps this from happening -> acts like “anti-gravity” Key concepts: Kinematics (relation between velocity, time, and distance), Electron orbits, Doppler effect –Nearly all galaxies have Doppler effect towards longer wavelengths -> “redshift” –Size of Doppler effect measures velocity –Velocity increases with distance: v = H d Imagine snapshot of middle of marathon

17. Expansion of Universe: Hubble’s Law Hubble’s data

18. Expansion of Universe: Hubble’s Law Key concepts: Kinematics, Electron orbits, Doppler effect, Gravity –All matter in universe attracts all other matter in universe via gravity -> expect expansion to decelerate (negative acceleration) –Measure velocity versus distance with supernovae Supernovae are “standard candles”: constant power Brightness tells you distance Doppler effect (redshift) tells you velocity –Observations show acceleration!!! Observations wrong? General relativity wrong? Dark energy? Produces “anti-gravity” similar to Einstein’s cosmological constant Imagine snapshot of middle of marathon

19. Expansion of Universe: Hubble’s Law

20. My research: Galaxy Clusters Key concepts: Gravity, Orbits, Light as Wave, Doppler effect, Temperature is Kinetic Energy –Massive ‘ball’ of galaxies, Doppler shift measures velocity, velocity measures mass Apply v = sqrt(GM/R) –Equate kinetic energy to temperature KE = (1/2)mv 2 = (3/2)kT Blackbody radiation -> m -> X-ray! –Hydrogen gas orbiting cluster emits X-rays! Measured temperature provides check of mass estimate

21. My research: Galaxy Clusters

22. Key concepts: Gravity, Orbits, Light as Wave, Doppler effect, Temperature is Kinetic Energy Galaxy clusters contain “fair sample” of stuff in the universe –Measure total mass with galaxy velocities, gas temperatures –Total starlight measures mass in stars –X-ray emission measures mass in diffuse gas –Total of (stars+gas) is only 15% of total mass! Difference is “dark matter” Evidence also from velocities of stars orbiting galaxies

23. My research: Galaxy Clusters

24. What do we know about dark matter? Behaves like “ordinary matter” in some ways –Clumps via gravitational collapse –Doesn’t provide pressure support (If you push normal matter together, it resists as the particles interact. Dark matter particles pass straight through each other without interacting) Similar to neutrinos, but neutrinos don’t have enough mass to be dark matter

25. My research: Galaxy Clusters Key concepts: Gravity, Orbits, Light as Wave, Doppler effect, Temperature is Kinetic Energy Largest structures in universe still forming today and in recent history Amount and nature of dark energy affects growth of structure –More dark energy (“anti-gravity”) means less growth of structure Measure amount of structure (number of clusters) in nearby universe –More clusters mean more structure Measure amount of structure in distant universe –Light travels at finite speed, so looking far away is looking into past Difference measures amount of growth, shows effects of dark energy

26. Signs of a bad observing run

27. My Goals for this Course Strengthen back and arm muscles with heavy textbook Cover several topics from first-semester physics courses Encourage independent thinking and group work, stimulate discussion Improve conceptual understanding as measured by pre and post-quiz Lay foundations for fall courses, MCAT Convince you that physics is comprehensible, interesting, and (sometimes) fun!

28. My Goals for this Course All met and far exceeded expectations Thank you for all your hard work and dedication!