Lecture 9: Cosmology Origin and Evolution of the Universe. Introduction to Astronomy and Astrophysics. Hubble and Expansion of the Universe

Transcription

1 Intrductin t Astrnmy and Astrphysics Lecture 9: Csmlgy Origin and Evlutin f the Universe Lectures Planets 1. Astrnmy and Observatinal Science 2. The Sun 3. Planets f the Slar System 4. Extra-slar Planets 5. Observing the Universe 6. Prperties f Stars 7. Life and Death f Stars 8. Galaxies and Large Scale Structure f the Universe 9. Csmlgy Origin and Evlutin f the Universe Overview: Expansin f the Universe Cluster f Stars Big Bang r Steady State? Csmic Backgrund Cluster f Galaxies Einstein s General Thery f Relativity Chapter 9 f Intrductin t Astrnmy and Csmlgy Hubble and Expansin f the Universe Einstein published General Thery f Relativity in In 1920s, Edwin Hubble shwed that the universe was expanding. The Einstein field equatin: Measured Dpper shifts t get velcities f galaxies. where Λ is the csmlgical cnstant which was intrduced t hld back gravity Einstein s greatest blunder. Einstein believed Universe was static but his equatins predicted expanding Universe. Frm Dpper shifts, can calculate galaxy velcity: Δλ v = λ c => v = c Δλ λ Sun where c is the speed f light. Galaxy

2 Galaxy Distances: Perid-Luminsity Relatinship Henrietta Leavitt ( ) discvered Cepheid variable stars. Frm perid f pulsatin, can determine luminsity called standard candle. Hubble and Expansin f the Universe Hubble pltted galaxy velcities (frm Dppler shifts) against galaxy distances (frm Cepheids). Belw shws a Cepheid variable lightcurve (left) and the peridluminsity relatinship (right). Page 288 f Mrisn. Can then use inverse square law t get distances. Shwed than distant galaxies were receding at a speed prprtinal t their distance. Gerges Lemaître therised an expanding universe such that Magnitude v = H 0 R where H 0 is Hubble s cnstant and R is distance. Implies we live in expanding Universe. Hubble age f the Universe Freidman Big Bang Mdels Assume Universe has expanded at unifrm rate thuut its existence. Can estimate time when it had nt size called the Hubble age. Hubble fund that H 0 = 500 km s -1 Mpc -1 Age f Universe is therefre: t 0 = 1 H 0 Hubble fund that t 0 ~ 2 billin years. Mdern value fr H 0 = 70.8 ± 1.6 km s -1 Mpc -1 => ~14 billin years. A. A. Friedman slved Einstein s equatins t prduce mdels f expanding universe. Knwn as Big Bang mdels, a dergatry by Fred Hyle. Universes begin in pint singularity. Initial high rate f expansin then falls with time due t the mutual gravitatin f all the matter in the universe. Critical r Flat universe is bundary between the pen and clsed universes. The universe then has a critical density If density is greater than this we have clsed universes which will eventually cllapse t a Big Crunch.

3 Freidman Big Bang Mdels Freidman Big Bang Mdels The rati f the actual density t the critical density is Ω = ρ / ρ critical If Ω > 1 => clsed universe. Space is psitively curved. Size f Universe If Ω < 1 => pen universe. Space is negatively curved. If Ω = 1 => critical universe. Space is flat Csmic Micrwave Backgrund Gerge Gamw: If rigin f Universe was very ht, shuld still be radiatin frm that time nw. Called the Csmic Micrwave Backgrund. Fr ~300,000 years, Universe t ht fr atms t frm. Matter and radiatin were interacting. S Universe was paque like a fg. Finally, it was cl enugh fr atms (H and He) t frm. Universe then became transparent s this is as far back in time as we can see. Csmic Micrwave Backgrund Radi astrnmers Arn Penzias and Rbert Wilsn serendipitusly discvered this backgrund radiatin in Using hrn radi antenna (left), they fund a blackbdy spectrum (right). Using Wien s Law: T = x 10-3 / λ max => T Universe = 2.7 K Radiatin then had the same temperature as matter (~3,000 K). It wuld have had a Black Bdy Spectrum with peak in the visible. Since then, Universe has expanded by 1000 times => temperature f this radiatin has fallen by the same rati s nw ~3K. λ max

4 Csmic Backgrund Explrer (COBE) COBE Blackbdy Spectrum f the Universe COBE was launched by NASA in 1989 and revlutinized ur understanding f early csms. It precisely measured and mapped the ldest light in the universe the csmic micrwave backgrund.. The results cnfirmed the Big Bang thery f the rigin f the universe. Read mre at COBE Blackbdy Spectrum f the Universe COBE Nbel Prize CMB is remnant f Big Bang. Minute temperature variatins (~150 micr-k) are linked t slight density variatins in early universe. Jhn Mather (belw) frm NASA Gddard Space Flight Center and Gerge Smt frm UC Berkeley win Nbel Prize in Physics fr COBE. These variatins are believed t have given rise t the structures that ppulate the universe tday: clusters f galaxies, as well as vast, empty regins.

5 ESA Planck Spacecraft Practical Task 9 Fllw ESA Launch t ISS Tday Planck studied the CMB mre sharply and sensitively than ever befre (temperature reslutin ΔT/T ~ 10-6). Launch frm Baiknur Csmdrme in Kasakhstan at 11:03 GMT this mrning. Determined the the spectrum f primrdial fluctuatin in the Big Bang and H0 = ± 1.2 km s-1 Mpc-1 => t0 = billin years. Watch live at Fund mre dark matter and a little less dark energy than previusly suppsed. Fllw at