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Two phases of WIMP dark matter annihilation in the First Stars

Two phases of WIMP dark matter annihilation in the First Stars. Fabio Iocco INAF/Osservatorio Astrofisico di Arcetri. In collaboration with: Bressan, E. Ripamonti, R. Schneider, A. Ferrara, P. Marigo S.C. Yoon, S. Akiyama. TeVPA 2008, Beijing , september 25 th.

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Two phases of WIMP dark matter annihilation in the First Stars

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  1. Two phases of WIMP dark matter annihilation in the First Stars Fabio Iocco INAF/Osservatorio Astrofisico di Arcetri In collaboration with: Bressan, E. Ripamonti, R. Schneider, A. Ferrara, P. Marigo S.C. Yoon, S. Akiyama TeVPA 2008, Beijing, september 25th

  2. The first stars (Population III) Form in halos of Mh106Msun at z20 (Tvir< 104K) First Starsprimordial chemical composition (BBN:noC,N,O-- A > 7) Weak cooling:H2 vs CObig masses No fragmentation, one star per halo Live fast, die young (30-300Msun go SNe) Hot: first engines for IGM Reionization (possibly) seed BH, correlated to quasars As of now, we have (very likely) not seen one yet Simulations! By courtesy of M. J. Turk

  3. Building the DM cusp Gas (collisional) cooling and collapsing to the center “pulling in” DM (gravitationally) (modeled through adiabatic contraction) Spolyar, Freese & Gondolo 07 (PRL 100, 2008) Iocco + 08 (also Freese+ 08)

  4. Powering the structure (with DM) Energy production DM profile critical! + Energy deposition Energy repartition for WIMP annihilation: 1/3 electrons 1/3 photons 1/3 neutrinos (lost) Absorption: Gas profile critical! Natarjan, Tan & O’ Shea 08

  5. (only)First Stars can do it ! At ngas~1012 #/cm3 (and above) structure opaque to annihilation products Spolyar, Freese & Gondolo 07 (PRL 100, 2008)

  6. What happens, then? 100 Msun initial conditions: R=1014cm ngas=1016 #/cm3 delicate equilibrium between accretion (or DM cusp build-up) and annihilation

  7. Evolving “Dark Stars” Adiabatic Contraction phase Acts at proto-stellar stages (or early pre-MS) at T 5000 K Adopted fiducial values: (mX=200GeV, shorter times)

  8. Scattering and capture Halo WIMPs (originally outside the star) are captured Captured WIMPs accumulate inside the star, thermalizing (needs some time) “sinking” to the center (most of annihilations is there) by scattering off the gas of the star

  9. Scattering: some more Capture rate depends on stellar characteristics And environemt (continuously capturing halo WIMPs)! Dark Matter annihilation inside first stars can overpower nuclear Needs continous replenishment!!!! Scott, Fairbairn & Edsjo 08 also excellent review DM in star can power only 10 yr!

  10. So what, once they become “DM burner” (/Dark Stars)? Active in late stages of pre-MS on Hayashi track KH < DM They don’t “need” to burn nuclear Iocco + 08 See also: Salati & Silk 89 (low-mass-analitical) Fairbairn, Scott, Edsjo 08 (ZAMS low-mass) Taoso, Berone, Meynet & Esktrom 08 Yoon, Iocco & Akiyama 08 Scott, Fairbairn, Edsjo 08

  11. Prolonged lifetimes DM powered stars are“frozen” as long as environmental DM stays supecritical Taoso, Bertone, Meynet & Ekstrom 08 frozen evolving SD0=10-38 cm2

  12. Direct observation?(surviving the ages) z (not actual size) Halo merger DM cusp erosion (baryons + self-annihilation) Bertone & Merritt 05 Wechsler + 02

  13. Some more properties(useful for indirect detection) # ionizing photons! (tricky: increase or decrease depending on DM density) Chemistry (yeah: analize that!) Yoon, Iocco & Akiyama 08

  14. Indirect observation?(surviving the models) Structure Formation: Collapse of the cloud Sources Feedback! UV IMF SFR Soft X-rays Metal Production H2 dissociation First studies on “Dark Stars” & Reionization; H2 formation Schleicher, Benerjee & Klessen 08 Cloud temperature Ionization of IGM

  15. Conclusions First phase of DM annihilation acts in proto-stellar phase, very likely transient. Yet to be explored in detail (depends mostly on <sv>) Capture phase at ZAMS or slightly earlier, potentially everlasting (strongly depends on SD -which is good-) Both phases are unlikely to be observed directly *but* studies on Reionization, 21cm, chemical evolution may help in the future…

  16. It is a field in its infancy! Mauro Maiuri, born august 19th 2008 Give us some more time, and stay tuned!

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