Transcript Dark Matter Capture in the first stars

Dark Matter in the Universe
Katherine Freese
Michigan Center for Theoretical Physics
University of Michigan
OUTLINE
• I) Review of Evidence for Dark Matter
• II) Dark Matter Detection: Are any of three claimed
detections right?
DAMA, HEAT, gamma-rays from galactic center
• Effect of mass distribution in Halo on detection:
Sagittarius stream can be a smoking gun for WIMP
detection
• III) DARK STARS: dark matter in the first stars
produces a new phase of stellar evolution!
Pie Chart of the Universe
The Dark Matter Problem:
• 90% of the mass in galaxies and
clusters of galaxies are made of an
unknown dark matter component
Known from: rotation curves,
gravitational lensing,
hot gas in clusters.
Our Galaxy:
The Milky Way
1012
The mass of the galaxy:
1012 solar
masses
Schematic
of Milky Way
Galaxies have Dark Matter
Haloes
Solar System Rotation Curve
Average Speeds of
the Planets
As you move out from
the Sun, speeds of the
planets drop.
Tyco Brahe
(1546-1601)
Lost his nose in a duel,
and wore a gold and
silver replacement.
Studied planetary orbits.
Died of a burst bladder
at a dinner with the king.
Rotation Curves of Galaxies
Orbit of a star in a
Galaxy: speed is
Determined by
Mass
Speed is determined by Mass
GM(r)

The speed at distance
r from the center of
the galaxy is determined
by the mass interior to
that radius. Larger mass
causes faster orbits.
Vera Rubin
Studied rotation curves
of galaxies, and found
that they are FLAT
95% of the matter in galaxies is
unknown dark matter
• Rotation Curves of Galaxies:
OBSERVED:
FLAT
ROTATION
CURVE
EXPECTED
FROM STARS
Sun’s orbit is sped up by dark
matter in the Milky Way
Lensing: Another way to
detect dark matter: it makes
light bend
Lensing by dark matter
Dark Matter in a Rich Cluster
Hot Gas in Clusters: The Coma Cluster
Without dark matter, the hot gas would evaporate.
Optical Image
X-ray Image from the ROSAT satellite
Dark Matter Candidates
•
•
•
•
•
•
•
MACHOs (massive compact halo objects)
WIMPs
Axions
Neutrinos (too light)
Primordial black holes
WIMPzillas
Kaluza Klein particles
Baryonic Dark Matter is NOT
enough
The Dark Matter is NOT
• Diffuse Hot Gas (would produce x-rays)
• Cool Neutral Hydrogen (see in quasar absorption
lines)
• Small lumps or snowballs of hydrogen (would
evaporate)
• Rocks or Dust (high metallicity)
(Hegyi and Olive 1986)
MACHOS
(Massive Compact Halo
Objects)
 Faint stars
 Planetary Objects (Brown Dwarfs)
 Stellar Remnants:
 White Dwarfs
 Neutron Stars
 Black Holes
Is Dark Matter Made of Stars?
NO!
• Faint Stars: Hubble Space Telescope
• Planetary Objects:
parallax data
microlensing experiments
Together, these objects make up less than
3% of the mass of the Milky Way.
(Graff and Freese 96)
MACHO AND EROS
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Is Dark Matter made of Stellar
Remnants (white dwarfs, neutron
stars, black holes)? partly
• Their progenitors overproduce infrared radiation.
• Their progenitors overproduce element abundances (C, N,
He)
• Enormous mass budget.
• Requires extreme properties to make them.
• NONE of the expected signatures of a stellar remnant
population is found.
• AT MOST 20% OF THE HALO CAN BE
MADE OF STELLAR REMNANTS
[Fields, Freese, and Graff (ApJ 2000, New Astron. 1998); Graff,
KF, Walker and Pinsonneault (ApJ Lett. 1999)]
Candidate MACHO microlensing event in
M87 (giant elliptical galaxy in VIRGO
cluster, 14 Mpc away)
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Baltz, Gondolo,
and Shara
(ApJ 2004)
Consistent with
MACHO data in
Milky Way (to LMC)
I HATE MACHOS!
DESPERATELY
LOOKING FOR WIMPS!
Good news: cosmologists
don't need to "invent" new
particle:
• Weakly Interacting
Massive Particles
(WIMPS). e.g.,neutralinos
• Axions
ma~10-(3-6) eV
arises in Peccei-Quinn
solution to strong-CP
problem
27 3
3

10
cm
/sec

h


v
2
AXIONS
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Axion masses
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AXION BOUNDS from ADMX
RF cavity experiment (1998)
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Overall status of axion bounds
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Inflation with the QCD axion
Chain Inflate:
Tunnel from
higher to lower
minimum in
stages, with a
fraction of an
efold at each
stage
Freese, Liu, and
Spolyar (2005)
V (a) = V0[1− cos (Na /v)] − η cos(a/v +γ)
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WIMPs
Relic Density: h2≈( 3x10-26 cm3/sec /27
sm
)
31
3
10
cm
s

h
v
Annihilation cross section sm of
Weak Interaction strength gives right
answer
2
v
Prospects for detection:
direct
Detectio
n
Neutrinos
from sun/earth
indirect
anomalous
cosmic rays
WIMP candidate motivated by SUSY:
Lightest Neutralino, LSP in MSSM
Supersymmetry
• Particle theory designed to keep particle
masses at the right values
• Every particle we know has a partner:
photon
photino
quark
squark
electron
selectron
• The lightest supersymmetric partner is a
dark matter candidate.
Lightest Super Symmetric
Particle: neutralino
• Most popular dark matter candidate.
• Mass 1Gev-10TeV
(canonical value 100GeV)
• Majorana particles: they are their own antiparticles and
thus annihilate with themselves
• Annihilation rate in the early universe determines the
density today.
• The annihilation rate comes purely from particle physics
and automatically gives the right answer for the relic
density!
Dark Matter Annihilation
• Annihilation mediated by weak
interaction.
• Thus for the standard neutralino
(WIMPS):
27
3
310 cm /sec
2
 h 
v ann
• On going searches: LHC, CDMS
XENON, GLAST, ICECUBE

SUSY dark matter
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Coannihilation included
(Binetruy, Girardi, and
Salati 1984);
Griest and Seckel 1991)
Detecting Dark Matter
Particles
• Accelerators
• Direct Detection
• Indirect Detection (Neutrinos)
• Sun (Silk,Olive,Srednicki ‘85)
• Earth (Freese ‘86; Krauss, Srednicki, Wilczek ‘86)
• Indirect Detection (Gamma Rays, positrons)
• Milky Way Halo (Ellis, KF et al ‘87)
• Galactic Center (Gondolo and Silk 2000)
• Anomalous signals seen in HEAT (e+), HESS,
CANGAROO, WMAP, EGRET, etc.
Detection of WIMP dark
matter
A WIMP in the Galaxy
travels through our
detectors. It hits a
nucleus, and deposits
a tiny amount of energy.
The nucleus recoils,
and we detect
this energy deposit.
Expected Rate: less than one count/kg/day!
Three claims of WIMP dark
matter detection: how can we
be sure?
• 1) The DAMA annual modulation
• 2) The HEAT positron excess
• 3) Gamma-rays from Galactic Center
HAS DARK MATTER BEEN
DISCOVERED?
The DAMA
Annual
Modulation
DAMA annual modulation
Drukier, Freese, and Spergel (PRD 1986);
Freese, Frieman, and Gould (PRD 1988)
Bernabei et al 2003
Data do show a 6 modulation
WIMP interpretation is controversial
DAMA/LIBRA
(April 17,
2008)
8 sigma
Event rate
(number of events)/(kg of detector)/(keV of recoil energy)
NT d
3


nv
f
(v,t)
d
v
 M dE
T
 0 F 2 (q)
f (v,t) 3

dv

2
2
v
ME
/
2

2m
v
dR

dE

Spin-independent  0 

Spin-dependent  0 

A 2 2

4 2

2
p
p
S p G p  S n Gn
2
DAMA: spin-independent?
Spin-independent
cross section with
canonical
Maxwellian halo
is excluded by
CDMS-II (2004)
EDELWEISS
DAMA
CDMS-II
Baltz&Gondolo
Bottino et al
2008
DAMA
CDMS
XENON
DAMA: spin-dependent?
(1) Neutron only
Savage, Gondolo, Freese 2004
DAMA: spin-dependent?
(2) Proton only
Savage, Gondolo, Freese 2004
DAMA: spin-dependent?
(3) Proton+neutron
Savage, Gondolo, Freese 2004
The HEAT
Positron Excess
Positron excess
• HEAT balloon found anomaly in
cosmic ray positron flux
• Explanation 1: dark matter
annihilation
• Explanation 2: we do not
understand cosmic ray
propagation
• Upcoming: PAMELA data
release, June 2008
Baltz, Edsjo, Freese, Gondolo 2001
Gamma-rays
from the Galactic
Center
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HESS Gamma-ray Data
Aharonian et al 2004
Neutralinos at Galactic Center?
mSUGRA study
Hall, Baltz, Gondolo 2004
• Compact source:
0.01 - 1 pc
• J~10 or 103
• Compatible with
mass from stellar
motions
Ghez et al 2003
Genzel et al 2003
WMAP microwave emission
interpreted as dark matter
annihilation in inner galaxy?
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Consistent with 100 GeV WIMPs.
Finkbeiner 2005
Gamma-ray line
• Characteristic of WIMP annihilation
• Need good energy resolution
GLAST Simulation
  
• GLAST may do
it below ~80 GeV

Bergstrom, Ullio and
Buckley 1998
Three Claims of WIMP
detection
• The DAMA annual modulation
• The HEAT positron excess
• Gamma-rays from Galactic Center
Upcoming Data
• LHC (find SUSY)
•
•
•
•
Indirect Detection due to annihilation:
GLAST first light May 27, 2008 (gamma rays)
PAMELA (positrons)
ICECUBE (neutrinos)
• Direct Detection: CDMS, XENON, WARP, CRESST, ZEPLIN,
COUPP, KIMS …
On GLAST
• First light, May 27, 2008
• DM annihilation to gamma rays
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Dark Matter Distribution in
Halo affects Signal in
Detectors
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Streams of WIMPs
• For example, leading tidal stream of
Sagittarius dwarf galaxy may pass through
Solar System
Majewski et al 2003, Newberg et al 2003
0.20
• Dark matter density in stream ~ 0.010.01
local
Freese, Gondolo, Newberg 2003
• New annual modulation of rate and endpoint
energy; difficult to mimic with lab effects
Lewis 2003
Freese, Gondolo, Newberg,
Sagittarius stream
Rate modulation
Endpoint energy modulation
Plot for 20% Sgr stream density (to make effect visible); p=2.7x10-42cm2
Sagittarius stream
Freese, Gondolo, Newberg 2003
Directional detection with DRIFT-II
Stream shifts peak date of annual modulation
Sagittarius stream
• Increases countrate in detectors up to
cutoff in energy spectrum
• Cutoff location moves in time
• Sticks out like a sore thumb in
directional detectors
• Changes date of peak in annual
modulation
• Smoking gun for WIMP detection
Dark Stars:
Dark Matter Annihilation in the
First Stars leads to a new phase
of stellar evolution.
Katherine Freese
Phys. Rev. Lett. 98, 010001 (2008)
D. Spolyar , K .Freese, and P. Gondolo
arXiv:0802.1724
K. Freese, D. Spolyar, and A. Aguirre
Also with P. Bodenheimer and N. Yoshida
Our Results
• Dark Matter (DM) in proto-stellar haloes can
dramatically alter the formation of the first
stars
• The LSP (lightest supersymmetric particle)
provides a heat source that prevents the
protostar from further collapse, leading to a
new stellar phase:
• The first stars in the universe are giant
(> 1 A.U.) H/He stars powered by dark matter
annihilation rather than by fusion
Basic Picture
• The first stars form in a DM rich environment
• As the gas cools and collapses to form the
first stars, the cloud pulls DM in as it
collapses.
• DM annihilates and annihilates more rapidly
as its densities increase
• At a high enough DM density, the DM heating
overwhelms any cooling mechanisms which
stops the cloud from continuing to cool and
collapse.
Basic Picture Continued
• Thus a gas cloud forms which is
supported by DM annihilation
• More DM and gas accretes onto the
initial core which potentially leads to a
very massive gas cloud supported by
DM annihilation.
• If it were fusion, we would call it a star.
• Hence the name Dark Star
• The First Stars- standard picture
• Dark Matter
• The LSP (lightest SUSY particle)
• Density Profile
• DM annihilation: a heat source that
overwhelms cooling in Pop III star formation
• Outcome: A new stellar phase
• Observable consequences
Dark Matter 
 Talk about Gas first
The First Stars
• Important for:
• End of Dark Ages.
• Reionize the universe.
• Provide enriched gas for later stellar
generations.
• May be precursors to black holes which power
quasars.
First Stars: Standard Picture
• Formation Basics:
– At z = 10-50
– Form inside DM haloes of (105-106) M
– Baryons initially only 15%
The dominant cooling Mechanism is H2
Not a very good coolant
(Hollenbach and McKee ‘79)
0.3 Mpc
Naoki Yoshida
Self-gravitating cloud
5pc
Yoshida
 Time increasing
 Density increasing
ABN 2002
A new born proto-star
with T* ~ 20,000K
r ~ 10 Rsun!
Thermal evolution of a primordial gas
adiabatic phase
Must be cool to collapse!
104
T [K]
H2 formation
line cooling
3-body
reaction
(NLTE)
103
loitering
(~LTE)
102
collision
induced
emission
adiabatic
contraction
Heat opaque to
release molecular
line
number density
opaque
to cont.
and
dissociation
Scales
• Jeans Mass ~ 1000 M
at
n  10 cm
4
3
• Central Core Mass (requires cooling)

 accretion
Final stellar Mass??
in standard picture
Dark Matter + Pop III Stars
• Dark Matter annihilation heats the
collapsing gas cloud preventing further
collapse, which halts the march toward
the main sequence.
- A “Dark Star” may result forming
(a new Stellar phase)
Dark Matter Annihilation
• Annihilation mediated by weak
interaction.
• Thus for the standard neutralino
(WIMPS):
27
3
310 cm /sec
2
 h 
v ann
• On going searches: LHC, CDMS
XENON, GLAST, ICECUBE

Dark Matter
26
Our Canonical Case:
vann 310 cm /sec
3
M  100GeV
Minimal supergravity (SUGRA)
– Mass 50GeV-2TeV
– v can be an order of magnitude bigger
ann


Nonthermal relics
–

vann can be much larger!
Dark Matter
• We consider a range:
– Mass: 1GeV-10TeV
– a range of Cross sections
• Results apply to other candidates
– Sterile 
– K-K particles
Dark Matter Density Profile
• Annihilation rate proportional to square
of dark matter density
• We need to know how much dark
matter is inside the star: what is the DM
profile?
Substructure 
NFW profile
Via Lactea 2006
Hierarchical Structure
Formation
Smallest objects form first
Pop III stars (105 M)
Merge  galaxies
Merge  clusters etc.
Numerical Simulations
• NFW Profile (Navarro,Frank,white ‘96)
(r)
  “Central Density”

(rs) 1/4 
r (1 r )2
rs
rs
rs 


“Scale Radius”
Other Variables
• We can exchange
, rs  Mvir, Cvir
•
Rvir

Rvir
Cvir 
rs
radius at which
DM  200 

4

3
Mvir 200
Rvir
crit(z)
3
The DM density of the universe at
the time of formation.
Dark Matter Density Profile
• Adiabatic contraction (a prescription):
– As baryons fall into core, DM particles
respond to potential well.
r M(r)  constant
• Profile
 (r) r1.9 Outside Core
that we find:
 (n)5 GeV (n/cm3)0.8

(using prescription from Blumenthal, Faber, Flores, and Primack ‘86)

 Time increasing
 Density increasing
ABN 2002
DM profile and Gas
Gas Profile
Envelope

Gas densities:
Black: 1016 cm-3
Red: 1013 cm-3
Green: 1010 cm-3

Blue: Original NFW Profile
Z=20 Cvir=2 M=7x105 M
ABN 2002
How accurate is Blumenthal
method for DM density profile?
• Work with Jerry Sellwood (in prep):
• There exist three adiabatic invariants.
• In spherical case, one is zero. Blumenthal
method conserves only angular momentum;
takes into account only circular orbits. With
Sellwood, also include radial orbits and
invariant. Find that our naivest results were
only high by 25%! Adiabatic conraction works
where it really shouldn’t.
Dark Matter Heating
Heating rate:
Qann n2 v  m
Fraction of annihilation energy
deposited in the gas:

2  v 
m
DMHeating fQ Qann


4
3
Previous work noted that at n10 cm
annihilation products simply escape
(Ripamonti,Mapelli,Ferrara 07)


1/3 electrons
fQ :
1/3 photons
1/3 neutrinos
Crucial Transition
• At sufficiently high densities, most of the annihilation energy is
trapped inside the core and heats it up
• When:
•
9
3
n
10
/cm
m 1 GeV 
m 100 GeV  n 1013 /cm3
1516
3
n
10
/cm
m 10 TeV 


The DM heating dominates over all cooling mechanisms,
of the core
impeding the further collapse



DM Heating dominates over cooling when the red lines
cross the blue/green lines (standard evolutionary tracks from
simulations). Then heating impedes further collapse.
DM  v 
m
vann 31026 cm 3 /sec


New Stellar Phase:
fueled by dark matter
Yoshida
et al ‘07
•
Yoshida etal. 2007
New Stellar Phase
• “Dark Star” supported by DM annihilation rather
than fusion
• They are giant diffuse stars that fill Earth’s orbit

m 1 GeV
core radius 960 a.u.
Mass 11 M
m 100 GeV
core radius 17 a.u.
Mass 0.6 M
• THE POWER OF DARKNESS: DM is only 2% of the
mass 
of the star but provides the heat source
• Dark stars
 are made of DM but are not dark:
they do shine, although they’re cooler than standard
early stars.
Luminosity 140 solar
Key Question: Lifetime of Dark
Stars
• How long does it take the DM in the core to annihilate away?
•
•
m
Te 



v


For example for our canonical case:
Te 600 million years for n 1013cm3
v.s. dynamical time of <103yr:
the core may fill in with DM again s.t. annihilation heating
continues for a longer time
Are there still some dark stars around today?


Possible effects
• Reionization: Delayed due to later formation
of Pop III stars? Can study with upcoming
measurements of 21 cm line.
• Solve big early black hole problem.
– Massive quasars at high z
Observables
• Dark stars are giant objects with core radii > 1 a.u.
– Find them with JWST:
NASA’s 4 billion dollar sequel to HST plans to see the first
stars and should be able to differentiate standard fusion
driven ones from dark stars, which will be cooler
•  annihilation products in AMANDA or ICECUBE?
Fluxes too low, angular resolution inadequate in
current detectors. Someday.
• Can neutralinos be discovered via dark stars or can
we learn more about their properties?
DARK STARs (in conclusion)
• The first Stars live in a DM rich
environment.
• DM annihilation heating in Pop III
protostars can delay/block their
production.
• A new stellar phase DARK STARS
Driven by DM annihilating and not by
fusion!
What happens next?
• Outer material accretes onto core
– Accretion shock
• Once T~106 K:
– Deuterium burning, pp chain, Helmholz
contraction, CNO cycle.
• Star reaches main sequence
– Pop III star formation is delayed.
Next stage
• Even once/if first star reaches main
sequence and has fusion in core, DM
annihilation can be very important.
• Can be dominant heat source
• Can determine the mass of the stars
(Freese, Spolyar, Aguirre Feb. 08;
Iocco Feb. 08)
Basic Idea
•
•
•
•
Dark star phase has ended
Next, fusion powered star forms: on main sequence
New star captures DM
Capture rate extremely high, which leads to a very
large luminosity from the DM.
• How big?
All first stars
1 M
Fixes mass of the first stars or limits DM scattering cross section.
Capture Rate (Particle Physics)
• Scattering
– Consider only SD scattering for first stars, which are made
only of H and He. SI scattering is generally subdominant.
Limits from
Super-K
•
and
m= 100 GeV
<v>ann=3x10-26 cm3/s
• DM luminosity LDM generally independent of DM
mass and annihilation rate!
Capture Rate (Astrophysics)
• Typical Mass of first stars
M ~ (10 to 250) M
– Up to 103 M (Jeans Mass)
MDM~106 M
• First stars DM host halo
• DM Velocity
– Much slower than Milky Way
since typical host halo is much smaller
• DM density
Simulations: 108 GeV/cm3
(Abel, Bryan, Norman 2002)
(Blumenthal, Faber, Flores,
Primack 1987)
Adiabatic Contraction: 1018
Gev/cm3
Capture Rate per Unit Volume
• n (number density of DM) cm-3
Press, Spergel 85 & Gould 88
• n (number density of H) cm-3
• V(r) escape velocity at a point r
•
velocity of the DM
• c scattering cross section
We can neglect the term in the
brackets because the DM velocity
is much less than the escape
velocity for the first stars, which
makes B big.
If the star moves relative to the DM halo, the term in the brackets changes.
Luckily, we can still neglect the term.
Capture Rate in the First Stars
Capture Rate s-1
1 Assume constant DM density
2 Conservatively fix v(r) to the escape from surface of star (vesc).
3 Integrate nH giving the number of H in the star, which
produces the second term in parentheses on the RHS below.
H fraction (fH)
Proton mass (Mp )
DM density ()
DM mass (m)
DM Luminosity (LDM)
• Equilibrium between the annihilation and Capture is very short
• Fraction of Energy deposited (f)- we assume a third goes
into neutrinos so we take f = (2/3).
Independent of the
mass of particle!
Comparison of Luminosity
If LDM exceeds Ledd, stellar mass is fixed!
70M 



250M
100M
50M
 10M
Black line- LEdd
Green line-LDM Blue line-L(fitted)
Red () zero metallicity stars on MS (Heger &Woosley)
LDM versus L
• We compare the DM luminosity against fusion
luminosity of zero metallicity stars half way through
H burning (on the main sequence) for various
masses. (Heger,Woosley, in prep)
– H burning represents the largest fraction of a star’s life.
• DM luminosity wins for a sufficiently high DM density.
Similar and Simultaneous Work
• Within a few days of each other, we and Fabio Iocco
posted the same basic idea:
– Both groups found that the DM luminosity can be larger than
fusion for the first stars.
• We went one step further:
– We found that when the DM luminosity exceeds the
Eddington luminosity, we can uniquely fix the mass of the
first stars.
Eddington Luminosity
•Luminosity of a star at which the radiation pressure
overwhelms the gravitational force.
C speed of light
p opacity
•Assume opacity (mean free path)
is dominated by Thompson scattering
since the surface of first stars is hot.
G Newton's Constant
M Stellar Mass
Max Stellar Mass
• Once LDM exceeds LEdd, star cannot accrete any
more matter and mass is determined.
• We can solve for the max stellar mass by setting
LEdd=LDM.
•
•
_ km/s
v=10
We derived the above by fixing
And also noting that (Vesc)2  (M)0.55,
which follows since R  (M)0.45
We find that the M
and c are inversely
related for a fixed
DM density.
Conclusions too
• Even if the Dark Star phase is short.
• DM Capture can still alter the first stars.
– DM luminosity larger than fusion
Luminosity
– May uniquely determine Mass of first stars
• Conversely- the first stars may offer the
best bounds or opportunity to measure
the the scattering cross section of DM.
Max Mass
10-38 cm2
10-40 cm2
10-43 cm2
Lines correspond to fixed scattering cross section. We show the
relationship between the DM density and mass of the first stars.
Max Mass Example
10-38 cm2
10-40 cm2
10-43 cm2
M=10M
=1014 Gev/cm3
Lines correspond to fixed cross section. We show the relationship
between the DM density and mass of the first stars.
First Stars: Limits on SD Scattering
Limits with Stellar Mass Larger than 1M
5x1012

Super K
Zeplin SI


Xenon SI
(SD limits examined in Savage, Freese, Gondolo 2005)
(GeV/cm3)
5x1015
(GeV/cm3)
1018
(GeV/cm3)
First Stars also limit SI Scattering
Limits with Stellar Mass Larger than 1M
5x1012
(GeV/cm3)
Super K
5x1015
Zeplin SI

(GeV/cm3)

CDMSII SI

Xenon SI
Present bounds from DMTools
1018
(GeV/cm3)
CONCLUSION
• Dark matter experiments are underway
• Already hints of detection?
• Dark Stars: new phase of stellar
evolution for the very first stars driven
by SUSY dark matter annihilation