Post on 07-Aug-2020
5 Dark matter and dark energy,
the Universe revealed
Our place
Courtesy: NASA
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
– a sphere attracts like a point mass located at its centre
213112
21 skgm1067.6, −−−×== Gd
mmGFm1 m2
attraction
Mass in a galaxy
• Courtesy ukdmc– UK dark matter
collaboration
http://hepwww.rl.ac.uk/ukdmc/dark_matter/rotation_curves.html
NGC 3198
• Stars only extend to 10 kpc• Radio doppler shift shows flat
rotation to 30+ kpcNGC 3198
Courtesy: http://bustard.phys.nd.edu/Phys171/lectures/dm.html
More evidence
• Galaxies have a high mass to luminosity ratio
Sungalaxies LM
LM
⎟⎠⎞
⎜⎝⎛×=⎟
⎠⎞
⎜⎝⎛ 20
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
Massive Particles NGC 4412 courtesy NASA: 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 supersymmetricparticles?
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
• 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
Galactic clustering
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– a fluid – quintessence– vacuum energy
Illustration source: http://www.roundtable.com/Critical_Path/Volume6/ignorance-of-
faculty.jpg
Our Universe• Ω0 = 1.02 ± 0.02• Ωm = 0.27 ± 0.04• Ωb = 0.044 ± 0.004• Ωr = 4.902×10-5
• 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 at 1026 atoms m-3?
Courtesy: Oxford APM survey http://www-astro.physics.ox.ac.uk/~wjs/apm_grey.gif
Galactic spatial density survey covering 2 million galaxies over an extensive part of the southern sky
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
Radial velocity
Transverse velocity
Earth
Star
Hipparcossurvey set the scene for milli-
arc second positional
surveys. Image source ESA
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
Classifying galaxies• Edwin Hubble
– Elliptical• E0 – E7
– Lenticular S0– Spiral
• ordinary Sa, Sb, Sc in order of decreasing spiral tightness
• barred SBa, SBb, SBc
– Irregular
Edwin Hubble (1889 – 1953)
NGC 3384 in Leo
M109, type SBc courtesy: http://seds.lpl.arizona.edu/messier/m/m109.html
Ellipticals
M49 NGC 4472 type E4 courtesy: http://www.noao.edu/image_gallery/images/d5/m49a.jpg
M60 NGC 4649 type E2 courtesy:
http://www.noao.edu/image_gallery/images/d6/m6
0a.jpg
M84, NGC4374 in the Virgo cluster, Type E1 courtesy: http://www.noao.edu/image_gallery/images/d5/m84.jpg
Spirals
M98, NGC4192 Type Sb in Coma Berenices Courtesy: http://www.noao.edu/image_gallery/images/d4/m98a.jpg
M99, NGC4254 Type Sc in Coma Berenices courtesy: http://www.noao.edu/image_gallery/images/d2/m99a.jp
g
M88, NGC4501 Type Sc in Coma Berenices Courtesy http://www.noao.edu/image_gallery/images/d3/m88a.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
Large Magellanic Cloud source:http://www.ast.cam.ac.uk/AAO/images/captions/uks014.html
Small Magellanic Cloud Source:http://www.ast.cam.ac.uk/AAO/images/captions/uks017.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