Two phases of WIMP dark matter annihilation in the First Stars
Fabio IoccoINAF/Osservatorio Astrofisico di Arcetri
TeVPA 2008, Beijing, september 25th
In collaboration with:A. Bressan, E. Ripamonti, R. Schneider, A. Ferrara, P. MarigoS.C. Yoon, S. Akiyama
The first stars (Population III)
Form in halos of Mh106Msun at z20 (Tvir< 104K)
First Stars primordial chemical composition (BBN: no C,N,O -- A > 7)
Weak cooling: H2 vs CO big massesNo 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
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)
Building the DM cusp
Powering the structure (with DM)
Energy production
DM profile critical!DM profile critical! + Energy deposition
Energy repartition for WIMP annihilation:
1/3 electrons1/3 photons
1/3 neutrinos (lost)
Absorption:Gas profile critical! Natarjan, Tan & O’ Shea 08
(only)(only) First Stars First Stars cancan do it ! do it !
Spolyar, Freese & Gondolo 07(PRL 100, 2008)
At ngas~1012 #/cm3
(and above)structure opaque
to annihilation products
What happens, then?
delicate equilibriumbetween accretion
(or DM cusp build-up)and annihilation
100 Msuninitial conditions:
R=1014cmngas=1016 #/cm3
Evolving “Dark Stars”
Adiabatic Contraction phaseActs at proto-stellar stages
(or early pre-MS)at T 5000 K
Adoptedfiducial values:
(mX=200GeV, shorter times)
Scattering and captureHalo WIMPs (originally outside
the star) are captured
by scattering off the gas of the starby scattering off the gas of the star
Captured WIMPs accumulate inside the star, thermalizing
(needs some time)
“sinking” to the center(most of annihilations is there)
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 reviewDM in star can power only 10 yr!
So what, once they become “DM burner” (/Dark Stars)?
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 08Yoon, Iocco & Akiyama 08Scott, Fairbairn, Edsjo 08
Active in late stages of pre-MSon Hayashi track KH < DM
Prolonged lifetimes
Taoso, Bertone, Meynet & Ekstrom 08
DM poweredstars are “frozenfrozen”
as long as environmental DM stays supecritical
frozen
evolving
SD0=10-38 cm2
Direct observation?(surviving the ages)
(not actual size)
Wechsler + 02Bertone & Merritt 05
Halo mergerDM cusp erosion
(baryons + self-annihilation)
z
Some more properties(useful for indirect detection)
# ionizing photons!(tricky: increase or decreasedepending on DM density)
Chemistry(yeah: analize that!)
Yoon, Iocco & Akiyama 08
Indirect observation?(surviving the models)
Sources
Structure Formation:Collapse of the cloud
Metal Production H2 dissociation
UV
Ionization of IGM
Soft X-rays
H2 formation
Cloud temperature
IMFSFR
Feedback!
First studies on “Dark Stars” & Reionization;
Schleicher, Benerjee & Klessen 08
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…
It is a field in its infancy!
Give us some more time, and stay tuned!
Mauro Maiuri, born august 19th 2008