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5 Dark Matter and Dark Energy, the Universe Revealed Courtesy: NASA 5 Dark matter and dark energy, the Universe revealed Courtesy: NASA Our place How much matter? • Add up all we can see – ~ 1 atom per 10 m-3 • Ω = 1? – ~ 1 atom m-3 • Dark matter – MACHOS – WIMPS The quintuplet cluster, courtesy NASA http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-000908.jpg What’s in the dark? • We can’t see everything • Dark matter in silhouette • Dark matter feels the force of gravity NGC 3314, courtesy NASA: http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-000893.jpg Newton’s law of Gravity • Every little bit of mass in the Universe attracts every other bit with a force • The force of attraction between two masses m1 and m2 is proportional to the product of the masses and the inverse square of the distance d between them attraction m m F = G 1 2 , G = 6 .67 × 10 −11 m 3 kg −1s − 2 d 2 m1 m2 – a sphere attracts like a point mass located at its centre Mass in a galaxy • Courtesy ukdmc – UK dark matter collaboration http://hepwww.rl.ac.uk/ukdmc/dark_matter/rotation_curves.html NGC 3198 Courtesy: http://bustard.phys.nd.edu/Phys171/lectures/dm.html • Stars only extend to 10 kpc • Radio doppler shift shows flat NGC 3198 rotation to 30+ kpc ⎛ M ⎞ ⎛ M ⎞ ⎜ ⎟ = 20×⎜ ⎟ More evidence L L ⎝ ⎠galaxies ⎝ ⎠Sun • Galaxies have a high mass to luminosity ratio MACHOS • Massive Compact Halo Objects – candidates: • red dwarves • brown dwarves • white dwarves • VMOs – very massive objects • SMOs – super massive objects • cold clouds of mainly hydrogen • primordial black holes – none of these account for all the ‘missing mass’ 23% of energy is dark matter • Most of it is not baryonic • WIMPS – Weakly Interactive NGC 4412 courtesy NASA: Massive Particles http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-000933.jpg Boulby mine • Dark matter wimp search – source: UKDMC – http://hepwww.rl.ac.uk/ukdmc /ukdmc.html Any more ideas? • Schematic of a spiral galaxy if we include dark matter • Are WIMPS supersymmetric particles? Source: http://bustard.phys.nd.edu/Phys171/lectures/dm.html Anglo Australian 2dF galaxy survey http://www.mso.anu.edu.au/2dFGRS/Public/ Part of the map of the Universe • The structure of the universe –every dot a galaxy • Part of the Sloan Survey of distant galaxies from z ≈ 0.05 to z ≈ 0.5 Courtesy: http://www.astro.princeton.edu/~mjuric/universe /p0.300.gif Galactic clustering • Clustering of mass is driven by gravity • Explanation of clustering is a major goal of modern astronomy Galaxies abound courtesy NASA http://grin.hq.nasa.gov/IMAGES/SMALL/GPN -2000-000912.jpg Dark Energy • Accelerating expansion of the universe • CosmoΛogical constant – Λ is negative – 1 = Ω0 = Ωm + ΩΛ – surely Ω is exactly 1? – zero energy in the Universe! • There are no good candidates for dark energy Illustration source: http://www.roundtable.com/Critical_Path/Volume6/ignorance-of- – a fluid – quintessence faculty.jpg – vacuum energy Our Universe • Ω0 = 1.02 ± 0.02 • Ωm = 0.27 ± 0.04 • Ωb = 0.044 ± 0.004 -5 • Ωr = 4.902×10 • Ων <0.015, • ΩΛ = 0.73 ± 0.04 • q0 = -0.60 ±0.02 • t0 = 13.7 ± 0.2 Gyr • baryons/photons is (6.1 ± 0.7)×10-10 • mneutrinos <0.23 eV • CMB z = 1088 ± 1 NGC 1316 courtesy NASA: http://imgsrc.hubblesite.org/hu/db/2005/11 /images/a/formats/large_web.jpg Clustering of mass • How did the universe progress from a few atoms m-3 to matter as we know it 26 -3 at 10 atoms m ? Galactic spatial density survey covering 2 million galaxies over an extensive part of the southern sky Courtesy: Oxford APM survey http://www- astro.physics.ox.ac.uk/~wjs/apm_grey.gif Clues to galaxy formation • Metallicity (Fe observed in a star’s spectrum) is a clue to density and age of surroundings of stars • Halo stars have low metallicity – hot dark matter and cold dark matter scenarios predict different populations of low metallicity stars • Distribution and velocity surveys are needed to mine the history of our galaxy Mapping dark matter • Develop the galactic rotational velocity idea to get more detailed velocity information for a much larger range of stars and structures • 10 km s-1 ≡ 2.75 milli-arc sec y-1 at 25,000 LY Hipparcos survey set the scene for milli- Transverse arc second velocity positional Star surveys. Image source ESA Earth Radial velocity http://sci.esa.int/science- e/www/object/index.cfm?f objectid=14060 Our galactic history • A story for the future Graphic of Milky Way galaxy courtesy NASA: http://solarsystem.nasa.gov/multimedia/gallery/MilkyWay.jpg Edwin Hubble Classifying galaxies (1889 – 1953) • Edwin Hubble – Elliptical NGC 3384 • E0 – E7 in Leo – Lenticular S0 – Spiral • ordinary Sa, Sb, Sc in order of decreasing spiral tightness • barred SBa, SBb, SBc – Irregular M109, type SBc courtesy: http://seds.lpl.arizona.edu/messier/m/m109.html M60 NGC 4649 type E2 Ellipticals courtesy: http://www.noao.edu/ima ge_gallery/images/d6/m6 0a.jpg M49 NGC 4472 type E4 courtesy: http://www.noao.edu/image_gallery/images/d5/m49a.jpg M84, NGC4374 in the Virgo cluster, Type E1 courtesy: http://www.noao.edu/image_gallery/images/d5/m84.jpg M88, NGC4501 Type Sc in Coma Berenices Courtesy Spirals http://www.noao.edu/image_gallery/images/d3/m88a.jpg M99, NGC4254 Type Sc in Coma Berenices courtesy: http://www.noao.edu/image_gallery/images/d2/m99a.jp g M98, NGC4192 Type Sb in Coma Berenices Courtesy: http://www.noao.edu/image_gallery/images/d4/m98a.jpg M65 type Sa Courtesy: AAO NGC 1232 • Sc galaxy in Eridanus • source: ESO M51 Courtesy: http://heritage.stsci.edu/2001/10/big.html Barred spirals M91, NGC4548 type SBb in Coma Berenices Courtesy: http://www.noao.edu/image_gallery/images/d6/m91a.jpg NGC 3185 type Sba Courtesy: http://astronote.org/note/files/objects/img/ngc3185.jpg NGC 3185 type SBc Courtesy: http://astronote.org/note/files/objects/img/ngc3185.jp g NGC 1365 One of the best barred spirals in the southern hemisphere Source: http://www.eso.org/outreach/press-rel/pr- 1999/phot-08a-99-preview.jpg NGC 1672 Courtesy: NASA/ESA Hubble Heritage; http://www.spacetelescope.org/images/html/heic0706a.html Irregular Small Magellanic Cloud Source: http://www.ast.cam.ac.uk/AAO/images/captions/uks017.html Large Magellanic Cloud source: http://www.ast.cam.ac.uk/AAO/images/captions/uks014.html Hubble’s tuning fork diagram • Original diagram suggested an evolutionary sequence • Not that simple Source: http://www.astr.ua.edu/preprints/white/gal_tuningfrk.html Tuning fork schematic Fig. 17.7, Courtesy: Kuhn & Koupelis Why spirals? • Effect is not a consequence of differential rotation • ~ 20 rotations around our galaxy for our Sun • Spiral pattern would be lost Fig. 16.19 Courtesy Kuhn & Koupelis Density waves Fig. 16.21 Courtesy: Kuhn & Koupelis.
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