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Announcements

Announcements. Last Observing Night tonight. Weather does not look promising.

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Announcements

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  1. Announcements • Last Observing Night tonight. Weather does not look promising. • Our final exam period is Monday May 6 @ 1:30pm. Will do project presentations first then Exam 4. Exam 4 will be all essay, probably five out of nine. It will cover Chapters 12 – 17. Sample essay questions will be posted by the end of the week.

  2. Dark Matter and Large Scale Structure

  3. Our Cosmic Address Our home galaxy: The Milky Way The Milky Way is one of several dozen galaxies in the Local Group

  4. The Virgo Cluster and Beyond The Virgo Cluster is the closest large galaxy cluster The Local Group, Virgo Cluster and several other galaxy clusters form the Local Supercluster

  5. The largest known structures are the galaxy filaments and voids

  6. Galaxies are the fundamental structures in cosmology

  7. After Recombination the universe experienced a Dark Age

  8. The First Stars end the Dark Age These stars would have been massive (200 – 400 Msun), living short lives and exploding in supernovae

  9. When and how did the first galaxies form? The first galaxies didn’t look anything like today’s galaxies. The first stars seeded them with “metal” but they would have been violent places with many mergers

  10. The earliest galaxies were probably small

  11. Mergers and collisions would have been common early on

  12. The Case for Dark Matter If the galaxies consisted of only luminous matter the velocity should fall off with distance from the nuclear bulge

  13. More Evidence of Dark Matter The total mass in the foreground galaxies lenses the background galaxies. Computations show there is far more mass present than is visible

  14. And even more evidence Hot intergalactic gas is held to the galaxy clusters by the gravity of more mass than is visible

  15. What is the Dark Matter? MACHO’s: Massive Compact Halo Objects MACHO’s are lone black holes, old neutron stars, cool white dwarfs and rogue planets. They can only account for a few percent of the dark matter

  16. Detecting MACHO’s While a number of MACHO’s have been detected, there aren’t enough of them to account for all the dark matter

  17. WIMP’s Weakly Interacting Massive Particles WIMP’s interact only through the weak nuclear force and gravity

  18. Neutrinos are WIMP’s Since they are moving at almost the speed of light they are hot dark matter

  19. Neutrino’s do have mass The best current experiments indicate a mass of an eV or less, depending on the type of neutrino

  20. Neutrino’s have been detected since the 1980’s The first detection of neutrino’s was at the Homestake Gold Mine in Lead SD

  21. Modern neutrino detectors can detect all neutrino flavors The Sudbury Neutrino Detector

  22. Cold WIMP’s Particle accelerators should produce them. While we won’t see the WIMP directly, we can detect its decay particles Solid state detectors held at near absolute zero should be able to detect them

  23. If a WIMP meets it’s antiparticle, they should annihilate

  24. While no direct detection of cold WIMP’s has occurred, there are limits on the possible mass

  25. Is the dark matter cold or hot? We know neutrino’s, which are hot dark matter, exist. Large numbers of them would have been created during Big Bang Nucleosynthesis and earlier. But, their mass is too small to significantly impact structure formation. Watch Structure Formation CDM video

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