dark matter in the universe katherine freese michigan center for theoretical physics university of...

Dark Matter in the Universe

Katherine FreeseMichigan Center for Theoretical PhysicsUniversity 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

The mass of the galaxy:

1210

1210 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 aGalaxy: speed is Determined by Mass

Speed is determined by Mass

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.

€

GM(r)

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:

EXPECTEDFROM STARS

OBSERVED:FLAT ROTATIONCURVE

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

Optical Image X-ray Image from the ROSAT satellite

Without dark matter, the hot gas would evaporate.

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 starsFaint stars

Planetary Objects (Brown Dwarfs)Planetary Objects (Brown Dwarfs) Stellar Remnants:Stellar Remnants: White DwarfsWhite Dwarfs Neutron StarsNeutron Stars Black HolesBlack 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

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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)



Baltz, Gondolo, and Shara (ApJ 2004)

Consistent withMACHO 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

v

cmhχ

sec/103 3272 ×≈Ω

AXIONS



Axion masses



AXION BOUNDS from ADMXRF cavity experiment (1998)



Overall status of axion bounds



Inflation with the QCD axion



V (a) = V0[1

Chain Inflate:Tunnel from higher to lower minimum in stages, with a fraction of an efold at each stage

Freese, Liu, and Spolyar (2005)

WIMPsWIMPsRelic Density: Ωχh2≈( 3x10-26 cm3/sec / χχsm)

vh

13272 scm103⋅≈Ω

v Annihilation cross section χχsm of Weak Interaction strength gives right answer

Prospects for detection:

Detection

direct

indirect

Neutrinosfrom sun/earth

anomalouscosmic 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 SymmetricParticle: 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):

• On going searches: LHC, CDMS XENON, GLAST, ICECUBE

€

Ωχh2 =

3×10−27 cm3 /sec

<σv>ann

SUSY dark matter



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 depositsa tiny amount of energy. The nucleus recoils, and we detectthis 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 modulationDrukier, Freese, and Spergel (PRD 1986); Freese, Frieman, and Gould (PRD 1988)

Data do show a 6 modulation

WIMP interpretation is controversial

Bernabei et al 2003

DAMA/LIBRA(April 17, 2008)8 sigma

Event rate

€

dR

dE=

NT

MT

×dσ

dE× nv f (v, t)d3v∫

(number of events)/(kg of detector)/(keV of recoil energy)

€

=ρ 0F

2(q)

2mμ 2

f (v, t)

vd3v

v> ME / 2μ 2∫

Spin-independent

Spin-dependent

€

0 =A2μ 2

μ p2

σ p

€

0 =4μ 2

πSp Gp + Sn Gn

2

DAMA: spin-independent?

Spin-independent cross section with canonical Maxwellian halo is excluded by CDMS-II (2004)

EDELWEISS

DAMA

CDMS-IIBaltz&GondoloBottino et al

CDMS

XENON

DAMA2008

DAMA: spin-dependent?Savage, Gondolo, Freese 2004(1) Neutron only

DAMA: spin-dependent?Savage, Gondolo, Freese 2004(2) Proton only

DAMA: spin-dependent?Savage, Gondolo, Freese 2004(3) Proton+neutron

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

HESS Gamma-ray DataAharonian et al 2004

Neutralinos at Galactic Center?

• Compact source: 0.01 - 1 pc• J~10 or 103

• Compatible with mass from stellar motions

Ghez et al 2003 Genzel et al 2003

mSUGRA studyHall, Baltz, Gondolo 2004

WMAP microwave emission interpreted as dark matter

annihilation in inner galaxy?



Finkbeiner 2005

Consistent with 100 GeV WIMPs.

Gamma-ray line

• Characteristic of WIMP annihilation• Need good energy resolution

GLAST Simulation

€

χχ → γγ• 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

Dark Matter Distribution in Halo affects Signal in

Detectors

Streams of WIMPs

• For example, leading tidal stream of Sagittarius dwarf galaxy may pass through Solar SystemMajewski et al 2003, Newberg et al 2003

• Dark matter density in stream ~ Freese, Gondolo, Newberg 2003• New annual modulation of rate and

endpoint energy; difficult to mimic with lab effects

Freese, Gondolo, Newberg, Lewis 2003

€

0.01−0.01+0.20 ρ local

Sagittarius stream

Plot for 20% Sgr stream density (to make effect visible); χp=2.7x10-42cm2

Rate modulation

Endpoint energy modulation

Sagittarius stream

Directional detection with DRIFT-IIFreese, Gondolo, Newberg 2003

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

arXiv:0802.1724K. Freese, D. Spolyar, and A. Aguirre

Phys. Rev. Lett. 98, 010001 (2008) D. Spolyar , K .Freese, and P. Gondolo

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)

Naoki Yoshida

0.3 Mpc

Yoshida

Self-gravitating cloud

5pc

ABN 2002

Time increasing

Density increasing

A new born proto-starwith T* ~ 20,000K

r ~ 10 Rsun!

Thermal evolution of a primordial gas

adiabatic contraction

H2 formationline cooling (NLTE)

loitering(~LTE)

3-bodyreactio

n

Heatreleas

e

opaque tomolecular

line

collisioninducedemissionT [K]

104

103

102

number density

opaqueto cont.

anddissociation

adiabatic phaseMust be cool to collapse!

Scales

• Jeans Mass ~ 1000 M

at

• Central Core Mass (requires cooling)

accretion

Final stellar Mass??

in standard picture

€

n ≈104cm−3

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):

• On going searches: LHC, CDMS XENON, GLAST, ICECUBE

€

Ωχh2 =

3×10−27 cm3 /sec

<σv>ann

Dark Matter

Our Canonical Case:

Minimal supergravity (SUGRA)– Mass 50GeV-2TeV– can be an order of magnitude bigger

Nonthermal relics– can be much larger!

€

<v>ann =3×10−26cm3 /sec

€

Mχ =100GeV

€

<v>ann

€

<v>ann

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?

Via Lactea 2006

Substructure

NFW profile

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)

€

ρ(r)= ρο

rrs

(1+ rrs

)2

€

ρο=

€

ρ(rs)= 1/4 ρο

€

rs= “Scale Radius”

“Central Density”

Other Variables

• We can exchange

• radius at which

€

ρο, rs → Mvir, Cvir

€

Rvir

€

ρDM = 200 × The DM density of the universe at

the time of formation.€

Cvir =Rvir

rs

€

Mvir =2004π3

Rvir3 ρcrit(z)

Dark Matter Density Profile

• Adiabatic contraction (a prescription):– As baryons fall into core, DM particles

respond to potential well.

• Profile

that we find: €

r M(r) = constant

€

ρχ(r)=r−1.9 Outside Core

€

ρχ(n)=5 GeV (n /cm−3)0.8

(using prescription from Blumenthal, Faber, Flores, and Primack ‘86)

ABN 2002

Time increasing

Density increasing

DM profile and Gas

Z=20 Cvir=2 M=7x105 M

Blue: Original NFW Profile

Gas ProfileEnvelope

Black: 1016 cm-3

Green: 1010 cm-3

Red: 1013 cm-3

Gas densities:

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:

Fraction of annihilation energy

deposited in the gas:

Previous work noted that at

annihilation products simply escape

(Ripamonti,Mapelli,Ferrara 07)

€

Qann =nχ2 <σv>× mχ

€

=ρχ

2 <σv>mχ

€

ΓDMHeating = fQ Qann

€

fQ :1/3 electrons

1/3 photons

1/3 neutrinos€

n≤104cm−3

Crucial Transition

• At sufficiently high densities, most of the annihilation energy is trapped inside the core and heats it up

• When:

• The DM heating dominates over all cooling mechanisms, impeding the further collapse of the core

€

mχ ≈1 GeV

€

mχ ≈100 GeV

€

mχ ≈10 TeV €

n ≈109 /cm3

€

n ≈1013 /cm3

€

n ≈1015−16 /cm3

DM Heating dominates over cooling when the red lines cross the blue/green lines (standard evolutionary tracks from

simulations). Then heating impedes further collapse.

€

<v>ann =3×10−26cm3 /sec

€

ΓDM ∝<σv>mχ

New Stellar Phase:fueled by dark matter

• Yoshida etal. 2007

Yoshida et al ‘07

New Stellar Phase

• “Dark Star” supported by DM annihilation rather than fusion

• They are giant diffuse stars that fill Earth’s orbit

• 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.

€

mχ ≈1 GeV

€

core radius 17 a.u.

Mass 11 M

€

mχ ≈100 GeV

€

core radius 960 a.u.

Mass 0.6 M

Luminosity 140 solar

Key Question: Lifetime of Dark Stars

• How long does it take the DM in the core to annihilate away?

• For example for our canonical case:

• 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?

€

Te ≈mχ

ρχ <σv>

€

Te ≈600 million years for n≈1013cm−3

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 STARSDriven 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.

• and

• DM luminosity LDM generally independent of DM mass and annihilation rate!

mχ= 100 GeV <v>ann=3x10-26 cm3/s

Limits from Super-K

Capture Rate (Astrophysics)

• Typical Mass of first stars– Up to 103 M (Jeans Mass)

• First stars DM host halo

• DM Velocity – Much slower than Milky Way since typical host halo is much smaller

• DM density

M ~ (10 to 250) M

MDM~106 M

Simulations: 108 GeV/cm3

Adiabatic Contraction: 1018 Gev/cm3(Blumenthal, Faber, Flores, Primack 1987)

(Abel, Bryan, Norman 2002)

Capture Rate per Unit Volume

• nχ (number density of DM) cm-3

• n (number density of H) cm-3

• V(r) escape velocity at a point r

• velocity of the DM

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.

• c scattering cross section

Press, Spergel 85 & Gould 88

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, whichproduces the second term in parentheses on the RHS below.

H fraction (fH) DM density (ρχ)

Proton mass (Mp ) DM mass (mχ)

DM Luminosity (LDM)

• Fraction of Energy deposited (f)- we assume a third goes into neutrinos so we take f = (2/3).

• Equilibrium between the annihilation and Capture is very short

Independent of the mass of particle!

Comparison of Luminosity

Black line- LEdd

Green line-LDM

If LDM exceeds Ledd, stellar mass is fixed!

Blue line-L(fitted)

Red () zero metallicity stars on MS (Heger &Woosley)

10M

50M

100M

250M

70M

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

G Newton's ConstantM Stellar Mass

•Assume opacity (mean free path)is dominated by Thompson scattering since the surface of first stars is hot.

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.

• We derived the above by fixing v=10 km/s • 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

Lines correspond to fixed cross section. We show the relationshipbetween the DM density and mass of the first stars.

M=10M

ρχ=1014 Gev/cm3

10-38 cm2 10-40 cm2 10-43 cm2

First Stars: Limits on SD ScatteringLimits with Stellar Mass Larger than 1M

5x1012

(GeV/cm3)

5x1015

(GeV/cm3)

1018

(GeV/cm3)Xenon SI

Zeplin SI

Super K

(SD limits examined in Savage, Freese, Gondolo 2005)

First Stars also limit SI Scattering

Super K

Limits with Stellar Mass Larger than 1M

5x1012

(GeV/cm3)

5x1015

(GeV/cm3)

1018

(GeV/cm3)Xenon SI

CDMSII SI

Zeplin SI

Present bounds from DMTools

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

dark matter in the universe katherine freese michigan center for theoretical physics university of...

Documents

dark matter slide

mass slide

dark matter detection

dark stars

universe slide

flat slide

dark matter haloes

baryonic dark matter