Look forward. Malcolm S. Longair s Galaxy Formation 2 nd edition [Library]

Transcription

1 Lk frward Why Study? : Hngsheng Zha and yu will be the st, and yu will be the st, Online ntes: star- take yur wn ntes (including blackbard lectures Malclm S. Lngair s Galaxy Frmatin nd editin [Library] Chpt -,5-8: expanding metrics, energy density, curvature, distances Chpt,,5,0: DM, Structure grwth, inflatin Chpt 9-0,3: Thermal Histry f Particle Reactin, Neutrins, WIMPs Text (intr): Andrew Liddle: Intr t Mdern (advanced): Jhn Peacck: Csmlgical Physics Web Lecture Ntes: Jhn Peacck, Ned Wright Fascinating questins: Birth, life, destiny f ur Universe Ht Big Bang --> ( 75% H, 5% He ) bserved in stars Frmatin f structure ( galaxies ) Technlgy -> much recent prgress: Precisin csmlgy: uncertainties f 50% --> % Deep mysteries remain: Dark Matter? Dark Energy? General Relativity wrng? Stretches yur mind: Curved expanding spaces, lking back in time, Observable Space-Time and Bands See What is ut there? In all Energy bands Pupil Galile s Lens 8m telescpes square km arrays Radi, Infrared ptical X-ray, Gamma-Ray (spectrum) The Visible Csms: a hierarchy f structure and mtin Csms in a cmputer Observe A Hierarchical Universe Planets mving arund stars; Stars gruped tgether, mving in a slw dance arund the center f galaxies. COBE satellites Grund Undergrund DM detectr Knw Hw were we created? XYZ & T? Us, CNO in Life, Sun, Milky Way, further and further first galaxy first star first Helium first quark Nw Billin years ag first secnd quantum rigin

2 Csmic Village The Milky Way and Andrmeda galaxies, alng with abut fifteen r sixteen smaller galaxies, frm what's knwn as the Lcal Grup f galaxies. The Lcal Grup sits near the uter edge f a supercluster, the Virg cluster. Hubble Deep Field: At faint magnitudes, we see thusands f Galaxies fr every star Galaxies themselves sme 00 billin f them in the bservable universe frm galaxy clusters bund by gravity as they jurney thrugh the vid. But the largest structures f all are superclusters, each cntaining thusands f galaxies and stretching many hundreds f millins f light years. are arranged in filament r sheet-like structures, between which are gigantic vids f seemingly empty space. the Milky Way and Andrmeda are mving tward each ther, the Lcal Grup is falling int the middle f the Virg cluster, and ~00 galaxies in the visible Universe ~00 stars per galaxy ~00 stars in the visible Universe the entire Virg cluster itself, is speeding tward a mass knwn nly as "The Great Attractr." Tday Intrducing Gravity and DM (Key players) Accelerating/Decelerating Expansin These structures and their mvements can't be explained purely by the expansin f the universe must be guided by the gravitatinal pull f matter. Visible matter is nt enugh ne mre player int ur hierarchical scenari: dark matter.

3 Csmlgists hpe t answer these questins: Lking Back in Time main cncepts in csmlgy Blah Hw ld is the universe? H 0 Why was it s smth? P(k), inflatin Hw did structures emerge frm smth? N-bdy Hw did galaxies frm? Hydr Expansin & Metric Csmlgical Redshift Energy density Will the universe expand frever? Omega, Lamda Or will it cllapse upn itself like a bubble? A few mins after New Year Celebratin at Trafalgar Square Feb t=5 days later D D 3 st cncept Metric: ant netwrk n expanding sphere D He C C C 3 3. He Hmgeneus Istrpic Universe Walking Elevating Earth Radius Stretching R(t) phi+dphi B A B A A 3 B 3 R(t) chi+dchi dl = [ R( t) d# ] + [ R( t)sin # d" ] A B 3 Angle χ Angle φ Expanding Radius R(t) Fundamental bservers,,3, with Fixed angular (c-mving) crdinates (χ,φ) n expanding spheres, distances given by Metric at csmic time t ds = c dt -dl, dl = R (t) (dχ + sin χ dφ ) 3

4 Stretch f phtn wavelength in expanding space Emitted with intrinsic wavelength λ 0 frm Galaxy A at time t<t nw in smaller universe R(t) < R nw Received at Galaxy B nw (t nw ) with λ λ / λ 0 = R nw /R(t) = +z(t) > Redshift Expansin is a stretching f space. The mre space there is between yu and a galaxy, the faster it appears t be mving away. Expansin stretches the wavelength f light, causing a galaxy s spectrum t be REDSHIFTED: STATIONARY: DOPPLER SHIFT: REDSHIFT: REDSHIFT IS NOT THE SAME AS DOPPLER SHIFT nd main cncept: Csmlgical Redshift The space/universe is expanding, Galaxies (pegs n grid pints) are receding frm each ther As a phtn travels thrugh space, its wavelength becmes stretched gradually with time. Phtns wave-packets are like links between grid pints This redshift is defined by: " z # = + z Galaxy Redshift Surveys Large Scale Structure: Empty vids ~50Mpc. Galaxies are in. Walls between vids.. Filaments where walls intersect. 3. Clusters where filaments intersect. Like Sap Bubbles df galaxy redshift survey z = 0 z = 0.3 Hubble law : V = H 0 d Hubble "cnstant": H km s Mpc Istrpic Expansin V (km/s) d (Mpc) Why WRONG? Extinctin by interstellar dust was nt then knwn, giving incrrect distances. Universal Expansin Hubble s law appears t vilate Cpernican Principle. we at a special lcatin? Milky Way Is everything mving away frm us? The Are

5 Universal Expansin Q : What is s special abut ur lcatin? A : Nthing Me Yu Accrding t Hubble s v Law: v v 3v I see: Yu see: 3v v v v The Universal Expansin An bserver in any galaxy sees all ther galaxies mving away, with the same Hubble law. Expansin (r cntractin) prduces a centre-less but dynamic Universe. E.g. Cnsider a quasar with redshift z=. Since the time the light left the quasar the universe has expanded by a factr f +z=3. At the epch when the light left the quasar, the distance between us and Virg (presently 5Mpc) was 5Mpc. the CMB temperature then (presently 3K) was 9K. the quasar appears receding with Dppler speed V=c. The quasar appears at a lk-back distance d = [t(0)-t(z)] c, where the lk-back time [t(0)-t(z)] ~ z/h 0 at small z<<, H 0 - =Taylr expansin ceff. nw + z = (wavelength) ( t) Rnw = R( t) (expansin factr) T( t) = (Phtn Blackbdy T " /, why?) T nw Hubble Law typical age (at z=) V = H 0 d t 0 d V = = Mpc km yr H 0 7 km/s Mpc s yr =3 Gyr. 3 rd cncept: The changing rate f expansin Newtnian Analgy: Cnsider a sphere f radius R(t), effective mass inside M = πρ R 3 /3 if energy density inside is =ρ(t) c. On this expanding sphere, a test m Kin.E. + Pt.E. = cnst Energy m (dr/dt) / G m M/R = (-k/)m c d Slpe = c Cnvert H as a frequency Hertz, find an integer clse t lg0(h)? Multiple chices -30, -0, 0, 0, 30. (dr/dt) /(c ) (πg/3)ρr /c =-k/ Unitless k <0, =0, >0 pen-flat-clse Newtnian expansin satisfies H = (dr/dt/r) = (ρ + ρ cur ) (8πG/3) the cst k absrbed in density ρ cur (t) = -k(ch 0 - /R) (3H 0 /8πG) ~ -k R - * cst Nw H = H 0 Lk back t 0 -t 5