Download Lecture 1 - Kavli IPMU

Dark Matter
a series of lectures at the crossroads
of particle physics, astronomy, and cosmology
Kai Martens
Kavli-IPMU
The University of Tokyo
Outline of the Lecture Series:
1.) Dark Matter: Early Evidence from the Motion of Stars and Galaxies
2.) Cosmology and Dark Matter (or: Why it is not Neutrinos)
3.) Nothing New? MOND, MACHOS, and Their Limitations
4.) Ideas from Particle Physics: Axions and WIMPs
5.) Direct Detection Experiments for WIMPs
6.) Seminar: The XMASS 800kg Dark Matter Experiment
7.) WIMP Annihilation: Indirect Detection Experiments
8.) Axion Experiments and Searches
Sept. 28, 2012
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Initital Remarks
science is a collaborative effort: communication is most important!
neither Japanese nor German are the international languages of science
→ English is (American English, that is...)
I will try to speak slowly and clearly,
and I would love it if you:
- ask questions during the lecture
- talk to me and/or asked questions after the lecture
- let me know if there is something that you do not understand
personal interaction is very important, especially among scientists;
if you really are too shy to talk:
my e-mail address is:
please start your subject line with:
Sept. 28, 2012
[email protected]
Konan: [your subject]
Kai Martens, Kavli-IPMU
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A Word About Myself
from: Frankfurt am Main, Germany
studied physics in Germany:
Vordiplom in Freiburg
PhD in Heidelberg:
PhD experiment: WA89 (Hyperon Beam Experiment)
@ CERN, Geneva:
PostDoc:
1990 – 1995
University of Tokyo (ICRR) & SUNY at Stony Brook
Super-Kamiokande & K2K:
1995 – 2000
Assistant/Associate Professor @ University of Utah, USA 2000 – 2008
experiments: HiRes, Flash (SLAC),
& Telescope Array
Associate Professor @ Kavli-IPMU, The University of Tokyo
experiment: XMASS
Sept. 28, 2012
Kai Martens, Kavli-IPMU
2008 – …
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Resources:
http://arxiv.org/
http://pdg.lbl.gov/
http://apod.nasa.gov/apod/astropix.html
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Outline of the First Lecture:
-
getting acquainted with each other:
-
-
the historical path:
-
-
discussion encouraged !!!
measuring the motion of stars and galaxies
evidence from our galaxy
evidence from clusters of galaxies
the local DM density
next lecture (this afternoon):
Sept. 28, 2012
Cosmology and Dark Matter
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Something to Keep in Mind:
skepticism, scepticism:
a personal disposition toward doubt or
incredulity of facts, persons, or institutions.
(http://www.thefreedictionary.com/scepticism)
http://pdg.lbl.gov/2011/reviews/rpp2011-rev-history-plots.pdf
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Solar System Orbits:
We know gravity.
1589 Galileo's experiment w/two balls
→ accerleration independent of mass
(according to: Vincenco Vivani, Galileo's student)
1687 Newton's Principia Mathematica:
F =G
m1 m2
r
2
note the scale:
AU
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Kai Martens, Kavli-IPMU
– not mm,
– not parsec
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How To Find Dark Objects...
which was the first astronomical object found based on
Newton's theory of gravitation?
Urbain Le Verrier, a french mathematician,
predicted Neptune's position applying
celestial mechanics, especially to Uranus
given Verrier's predictions the planet
Neptune was observed with the telescope at the
Berlin Observatory in the night of Sept. 23, 1846
great success:
gravity works!
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Not Always Though:
planet Mercury:
precession of the perihelion:
why???
postulate: planet “Vulcan”...
but that was the wrong answer;
the right one is:
general relativity's bent space
near the Sun...
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Circular Orbits and Mass:
1.7e-7
solar mass:
2x1030kg
2.4e-6
3.0e-6
planetary masses
as fraction of solar
3.2e-7
9.5e-4
2.9e-4
4.4e-5 5.0e-5 7.5e-9
velocity
Keplerian orbits
to measure enclosed mass → measure orbital velocity
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Milky Way Galaxy
Milky Way:
~ 3x1011 stars
~ 1x1012 M⊙
~ 100 kly across
type: SBc
barred spiral
Sun:
orbital period: ~200My
distance to center:
27.2 kly (8.3kpc)
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Velocity Dispersion and Mass
galaxy (Milky Way...) stable; stars are “bound” to it.
Q: How to get away?
A: Run fast (escape velocity...) !
general idea:
measure velocities of those who are bound
→ infer how strong the bond is
Mm
F =G 2
r
gravitational bond
→ how big is the mass that binds
statistical power:
→ need many objects, know their mass !!!
→ distribution of velocities:
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(Gaussian:)
μ, σ
Kai Martens, Kavli-IPMU
← “dispersion”
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The Mass of Stars:
we understand stars:
- color represents temperature
- temperature represents mass:
for main sequence !!!
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Starlight and Temperature:
Wien's law: max  1/T
Sun's surface: 5778 K
solar
spectrum
(above atmosphere)
absorption
lines: velocity!
blue stars: 30,000K – 60,000K O
blue-white stars: 10,000K – 30,000K B
white stars: 7,500K – 10,000K A
yellow-white stars: 6,000K – 7,500K F
yellow stars (Sun): 5,000K – 6,000K G
yellow-orange stars: 3,500K – 5,000K K
red stars: < 3,500K M
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For Example: Hydrogen Lines
absorption spectrum:
emission spectrum
photons (light): Eph = hfph = hc/ ph
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Relative Velocity: Doppler Effect
if the source of the light is in motion towards or away from the observer,
spectral lines become blue- or red-shifted:
λ obs
v rel
=1+
λ em
c
only radial
motion becomes
measurable;
lateral
does not:
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Velocity of Stars, Galaxies, Clusters:
λ obs
v rel
=1+
λ em
c
BAS11:
20 dense galaxy clusters
> 10,000 galaxies
~ 1 GLy away
note: the whole pattern moves
without pattern (single line): which one is it ???
(sorry, could not find
a picture of the
supercluster; on the other hand: if its clusters were resolved...)
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Perpendicular to Galactic Plane:
use “vertical acceleration” (Oort Criterium)
to measure local density (mass/volume):
type of star
A
K giants
M dwarfs
dispersion
[km/s]
scale height
[pc]
9
17
18
120
270
350
blue stars: 30,000K – 60,000K O
scale height:
different stars →
different distribution
around plane
blue-white stars: 10,000K – 30,000K B
white stars: 7,500K – 10,000K A
yellow-white stars: 6,000K – 7,500K F
yellow stars (Sun): 5,000K – 6,000K G
yellow-orange stars: 3,500K – 5,000K K
(not trivial !!!)
red stars: < 3,500K M
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1932: Stars in Galactic Neighborhood
1932: Jan Oort (Leiden, Netherlands) measures velocities of stars
in our galactic neighborhood:
gravitational mass
needed to keep them in the galactic plane:
3
~ 1M⊙/375ly > 2mstars,visible
→ dark matter
same approach, better telescopes (star catalogues, Hipparcos)
→ local density today!
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Clusters of Galaxies: Virial Theorem
here gravitational mass is derived from the
motion of the member galaxies:
cluster → same distance → red-shift dispersion due to relative motion
stable system (!), averaged over time:
T = total kinetic energy,
V = total potential energy
2 T =−∑ F⃗ i⋅r⃗i
V ( r )=ar
n
2 T =n V tot
→ calculate mass required to keep together (cluster)
→ compare to luminous mass in cluster (galaxies and gas...)
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1933: Coma Cluster of Galaxies
Fritz Zwicky (Caltech, USA):
virial theorem: ΣT = ½ ΣU
→ galaxies in Coma cluster
too fast for cluster's
gravitational potential
→ dark matter
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contamination:
forground/background
galaxies
bias:
unobserved galaxies
~ 90% of mass
in cluster is dark
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http://apod.nasa.gov/apod/ap100502.html
Today: Galaxies in the Coma Cluster
Coma Cluster:
- thousands of galaxies, mostly ellipticals
- each galaxy: billions of stars ...
- millions of Ly across, 321 MLy away:
redshift 0.0231 (6.925 km/s), velocity dispersion: 1000 km/s
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