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The Role of Neutrinos in Galaxy Formation

The Role of Neutrinos in Galaxy Formation. Katherine Cook and Natalie Johnson. http://zebu.uoregon.edu/1999/ph123/lec08.html. http://astro.ph.unimelb.edu.au/~mdrinkwa/lectures/pgc_astro98/galaxy_form/part01. html. Mommy, Where Do Galaxies Come From?. 1-2. 3. 4-7. 8.

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The Role of Neutrinos in Galaxy Formation

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  1. The Role of Neutrinos in Galaxy Formation Katherine Cook and Natalie Johnson http://zebu.uoregon.edu/1999/ph123/lec08.html

  2. http://astro.ph.unimelb.edu.au/~mdrinkwa/lectures/pgc_astro98/galaxy_form/part01.htmlhttp://astro.ph.unimelb.edu.au/~mdrinkwa/lectures/pgc_astro98/galaxy_form/part01.html Mommy, Where Do Galaxies Come From?

  3. 1-2 3 4-7 8 Expansion in the Early Universe • Chronology of Key Events: • Graviton separated first—gravity! • Strong force broke away next—quarks! • Electroweak force splits into electromagnetic and weak forces—bosons and photons! • Cosmic Microwave Background formed • Muons, electrons and neutrinos created. • Universe was completely plasma. • Energy density decreased faster than matter density and matter began clumping. • Recombination- hydrogen formed!

  4. Evolution of Galaxy Clusters Hot clouds of gas merge and clump together under the force of gravity to form large-scale structures: http://zebu.uoregon.edu/1999/ph123/nbod2.mpg

  5. Processes of Galaxy Formation But where did the necessary density perturbations come from in the first place to form these massive galaxies?

  6. Cosmic Microwave Background Radiation • Isotropic to 1 part in 105 at a temperature of 2.725 K • This background radiation is almost too smooth to account for density fluctuations. • Could dark matter have clumped together before luminous matter and provided the needed density contrast? (Longair, 106)

  7. http://zebu.uoregon.edu/1999/ph123/lec08.html Why There Must be Dark Matter • Rotation Curves • X-Ray Observations • Tidal Forces • Inflationary Theory Predicts Density Parameter=1 • Gravitational Lensing

  8. Critical Density • The universe might expand forever and ever Ω<1 • The universe might nearly cease expansion Ω=1 • The universe might reverse its acceleration, resulting in a really really big crunch Ω>1 (Longair, 125)

  9. Dark Matter is Concentrated in Envelopes or Halos Around Galaxies • Kepler’s Third Law P2 = a3/ (m1+m2) yields over 90% of the Milky Way’s mass in its outer regions

  10. The Creation of Dark Matter Halos http://zebu.uoregon.edu/1999/ph123/images/halo.mpg

  11. Hot Dark Matter vs. Cold • HDM • Particles moving at nearly the speed of light, like neutrinos • Difficult to explain matter clumping– must be top-down structural formation • CDM • Slow-moving particles, such as WIMPS • Make galaxies too well– bottom-up approach to large-scale formation

  12. Dark Matter Candidates MACHOs WIMPs Neutrinos The speaker known as “Natalie” will now be replaced by “Katherine”.

  13. MACHOs • Massive Compact Halo Objects • Planets • Small, dim stars • Small black holes • Detected through Gravitational Lensing • Incidences too small to account for enough dark matter

  14. WIMPs • Weakly Interacting Massive Particles • Gauge bosons • Higgs bosons • Entirely Undetected

  15. Neutrinos • Neutrinos are neutral, carry energy, and have mass • Three types of neutrinos-muon neutrinos, tau neutrinos, and electron neutrinos-corresponding to the other members of the lepton family of particles

  16. Neutrinos As Dark Matter Neutrinos are a plausible candidate because • There are so many of them (~10^90) These were created in the big bang when the electroweak force decoupled into the electromagnetic force and the weak force • They have mass (albeit very small), ~0.05 eV

  17. Interesting Points Interesting Point One • If dark matter is mostly neutrinos, then the neutrinos are NOT uniformly distributed throughout space Interesting Point Two • Neutrino density might be able to close the universe

  18. The Milky Way has a mass deficiency of 1041kg If that were just neutrinos, there would be about 1078 neutrinos in the Milky Way Uniformly distributed, there are about 1012 neutrinos per meter cubed of space That would mean only 1051 neutrinos occupying the Milky Way The Milky Way and The Neutrino

  19. Neutrinos Will Close the Universe! • Check This Out Critical density ρc is 1.1*10-26kg/m3 Mass density of the universe ρm is given by luminous matter density plus dark matter density (~3*10-29kg/m3) + (4.5*10-25kg/m3) ~ 4.5*10-25kg/m3 Ω0 = ρm/ρc ~ 101 101>>1!!!, which could result in…

  20. So, can Neutrinos Help Explain Galaxy Formation? • Jean’s Instability • Simulations • Must investigate cosmions and the early Universe • Properties of dark matter (neutrino) clumping • Mean-free path

  21. Questions and Further Investigations • Will Nestle soon be marketing a candy bar dubbed the Neutrino to accompany the already famed ?

  22. ) d candy bar ò( + = ? Key Chocolate = x0 Peanuts = x1 Peanut butter = x2 Caramel = x3 Nougat = x4 Crispies = x5 Almonds = x6 Toffee = x7

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