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PCS 181 (141)
Lecture 3

# Introduction to Astronomy-Lecture 3 Notes!.docx

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Department
Physics
Course Code
PCS 181
Professor
Margaret Buckby

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The History of the Universe: Time after Big Bang: Event:  < 1 s, T = 1 x 10 K2 - All types of elementary particles in existence. 1000 Particle transmutations occur.  4 s. -Matter and anti-matter begin annihilation to produce energetic photons.  *NOTE: NO SPACE MEANS NO TIME! REPORT TOPICS: BIG MASSIVE BLACKHOLES AND HAWKING RADITATION.  3 Minutes. -Neutrons and protons fuse to form Helium NUCLEI.  30 Minutes. -Elementary particle transmutations cease.  380,000 years, T = 3000 K -Recombination Era = photon energies have declined enough such that Hydrogen and Helium ATOMS can survive.  1 x 10 years. -Galaxies form. 9  2 x 10 years. -Stars form.  [?] Years. -Present time = Age of the Universe. The Age of the Universe: Hubble Time: Recall the Hubble Law: V r H dowhere we use a Hubble parameter of 75 km/s Mpc Recall that d = Vt and replace d in above equation: V = H ot 1 = H o t = 1/Ho= Hubble time = Age of Universe. Hubble Time: t = 1 = t = Mpc 75 km/s 75 km/s Mpc = t = 3.09 x 10 km = t = 4.12 x 10 s = t =13.1 x 10 years. 75 km/s *NOTE: TODAY IT IS = t = 13.8 x 10 years.  Open Universe: Density of matter is low = gravity is weak = universe expands forever.  Closed Universe: Density of matter is high = gravity will halt the expansion and re- contract the universe. If this happens repeatedly, we have an oscillating universe.  Flat Universe: Universe contains the so-called Critical density of matter = galaxies barely manage to AVOID re-collapse. Future of an Open or Flat Universe: Time after Big Bang: Situation: 12 1) 1 x 10 years. -Hydrogen and Helium are depleted so that no new stars can form. 14 2) 1 x 10 years. -Existing stars run out of fuel. 3) 1 x 10 years. -All stars will have experienced ~100 disruptive encounters, flinging their planets into space. 18 4) 1 x 10 years. -Evaporations of stars and collapse of galaxies into black holes at their centers. 30 + + 5) 1 x 10 years. -Protons decay (???). p = e + v (a positron and neutrino). 6) 1 x 10 100years. –Hawking = Black Holes decay. 7) Far Future. -The Big Frizzle = an ever-expanding gas of electrons, protons, neutrons, photons. Future of a Closed or Oscillating Universe: 1) The expansion phase is the same as statements. a) Though 5. Above. 2) At some unknown future time, re-contraction begins. Faraway groups of galaxies become blue-shifted, the density of the universe increases, black holes increase in
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