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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 QuickTime™ and a TIFF (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) QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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 QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Axion masses QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. AXION BOUNDS from ADMX RF cavity experiment (1998) QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Overall status of axion bounds QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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) QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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 3 310 cm /sec 2 h v ann • On going searches: LHC, CDMS XENON, GLAST, ICECUBE SUSY dark matter QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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 Sn 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 QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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? QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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 QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. Dark Matter Distribution in Halo affects Signal in Detectors QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. 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 ~ 0.010.01 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 3 310 cm /sec 2 h v ann • On going searches: LHC, CDMS XENON, GLAST, ICECUBE Dark Matter 26 Our Canonical Case: vann 310 cm /sec 3 M 100GeV Minimal supergravity (SUGRA) – Mass 50GeV-2TeV – v can be an order of magnitude bigger ann Nonthermal relics – vann 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 rs 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)r1.9 Outside Core that we find: (n)5 GeV (n/cm3)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 n2 v m Fraction of annihilation energy deposited in the gas: 2 v m DMHeating fQ Qann 4 3 Previous work noted that at n10 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 1516 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 vann 31026 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 1013cm3 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