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