Black Holes as DM annihilation “boosters” · Inserting typical values for the DM candidate and...

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8/28/06 G. Bertone, BHs as DM annihilation “boosters”, TeVPA II Madison, WI 1

Black Holes as DM annihilation “boosters”

Gianfranco BERTONE

INFN, Padova

[email protected]

http://home.fnal.gov/~bertone

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True surface density of DM, Moore et al. 2005

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But annihilation fluxes depend on the density SQUARED

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But this is a very naïve picture!•Potential wells near galactic centers are dominated by baryons•Black Holes are ubiquitous and dominate the innermost regions•Take advantage of new developments in Astrophysics andCosmology

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Given all these uncertainties (plus the particle physicsuncertainties):

How can you convince particle physicists thatyou have actually discovered DM?

i.e. can Astrophysics provide a smoking-gun signature for DM?

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(Somewhat arbitrary)

Black Holes: Definitions

Stellar Mass BHs

•Endpoint of stellar evolution•Indirectly observed•Robust evidence•Lower limits on mass from obs.

Intermediate Mass BHs

•Maybe form in Glob. clusters•Maybe observed as ULXs•Seed for SMBHs?•Speculative but probable!

Supermassive BHs

•Unknown origin•Ubiquitous!•Robust evidence•Mass correlated with host halo

M ≤ 102 M 102 M ≤ M ≤ 106 M 106 M ≤ M ≤ 109 M

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Convincing evidence for BHs, right in our (cosmic) backyard

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Where do the observed BHs come from?

CREDIT: Sloan Digital Sky Survey, Apache Point Observatory

•We don’t know! Butthey are ubiquitous

•High-redshift quasarssuggest that 109 MsunBHs were already inplace when the Universewas only 1Gyr old

•Circumstance that canbe understood in termsof rapid growth startingfrom massive seeds

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Scenario I: Seeds of 102 Msun

•At z ≈18, first stars form (image:formation of a protostar, fromhttp://www.tomabel.com)

•Zero metallicity Pop III starswith masses in the range M ⋲ 60 -140 Msun and M > 260 Msuncollapse directly to black holes

•Stars with 140 < M/ Msun < 260disrupted by pulsation pairproduction instability, leavingbehind no remnant

Gebhardt, Rich, & Ho 2002, Heger,Fryer, Woosley, Langer and Hartmann2003; Madau & Rees 2001; Islam Taylor& Silk 2003

http://www.tomabel.com

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Scenario II: Seeds of 105 Msun

•In halos with efficientmolecular hydrogen coolingand which do not experienceany major mergers, aprotogalactic disk forms andcan evolve uninterrupted.

•Effective viscosity transfersmass inward

•A baryonic mass of order 105

Msun loses its angularmomentum and is transferredto the center of the halo.

•Central object may be brieflypressure-supported, but iteventually collapses to form ablack hole

Koushiappas, Bullock & Dekel 2004

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Conserve Mass & Angular Momentum:

γsp=!

Mf

iM

*Adiabatic* growth of a Black Hole:BHs as “Annihilation Boosters”!

9-2γ4-γ

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Collisional growth of Spikes (in presence of Stellar Cusps)

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An intuitive description of Dark Matter “Spikes”

GB & Merritt 2005

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Populating the MW halo with mini-spikes

GB 2006

•Populate halos at high z with prescription from given IMBHs model

•Evolve mini-halos with semi-analytic codes (Zentner, Bullock 2003, Zentner et al. 2004)

•Obtain statistical realization of MW halo at z=0 (RED dots)

•Iterate (BLUE dots)

•Average results over realizations (GB, Zentner & Silk 2005)

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Gamma-Rays from DM Mini-spikes around IMBHs

Inserting typical values for the DM candidate and the spike, we find inscenario II

•One would naïvely expect that the flux scales with σv/m2

•BUT The maximum density is higher for the pessimistic case, andrcut=rcut(m,\sigma v). This partially compensates for the decrease in fluxdue to the prefactor σv/m2

•The final luminosity of the objects is thus proportional to ~ (σv)2/7m−9/7

KEY POINT!

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Gamma-Rays from DM Mini-spikes

Inserting typical values for the DM candidate and the spike, we find inscenario II

Note the normalization of the flux:

Each Black Hole would be as luminous

(in terms of annihilation radiation) as the whole Galaxy!!

KEY POINT!

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IMBH Scenario 2 (105 Msun)

GB, Zentner & Silk 2005

Results:

•Very high fluxes!

•Sources off the disk(need large field ofview to search forthem)

•Tens of sources withIDENTICAL spectrum:smoking-gun for DM

•Scatter amongdifferent realizationsrelatively small

•Can use ACTs tostudy sources ≥ 300GeV

Smoking gun!

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IMBH Scenario 2 (103 Msun)


Alternative strategy:

Use MAGIC or otherACTs to re-observeselected unidentifiedEGRET (and GLAST…)sources.

Criteria for EGRET:

• Off the disk

• Appropriate spectrum

• Extrapolate spectra athigh energies for areasonable guess onthe detectability

Ongoing collaborationwith MAGIC group

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Probe high mχ with ACTsFull-sky search with GLAST

Observational Strategies

HESS

MAGIC

VERITASFull-sky search, simulation

of sources and spectra

G. Busetto, R. Rando

Re-observation of EGRET

sources, selection of candidates

M. Doro, M. Gaug, M. Mariotti, V. Scalzotto

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Antares IceCube

Interesting alternative: Neutrino Telescopes

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Prospects for detection with Neutrino Telescopes

GB 2006

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C O N C L U S I O N S

• BHs can effectively “boost” the DM annihilation signal

• Intermediate Mass Black Holes may represent a uniqueopportunity to discover Dark Matter particles

• GLAST can rule out this scenario or prove it right.Importance of ACTs (MAGIC, HESS, VERITAS,CANGAROO) in extending the search at higher energies

• Neutrino telescopes IceCube and ANTARES might be ableto detect neutrinos from mini-spikes

• Further applications: see talks of S. Ando (gamma-raybackground) and P. Brun (anti-matter) in the DM session!

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Why “annihilations”?

Early Universe

X

Today

X

X

X

SM

SM

SM

SM

Rough estimate of the relic density:

Electroweak-scale cross sections can reproduce correct relicdensity. LSP in SUSY scenarios KK DM in UED scenarios are OK!!

X = DARK MATTER SM = STANDARD MODEL PARTICLE

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Spectrum per annihilation


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Annihilation Radiation

Direct productionHadronization and

decay

Neutrinos•direct production

•decay of heavy quarks•hadronization followed by decay of charged pions,

PhotonsDirect production

Hadronization thenDecay of neutral pions

e+e- pairsDirect production

Hadronization thenDecay of charged pions

Initial State (X= χ or B(1))Relevant final states

X

X

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Interesting applications: Work in progress…

Ahn, Bertone, Merritt & Zhang 2006 Bertone, Brun & Salati 2006

Gamma-ray Background Anti-matter searches

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Black Holes as DM annihilation “boosters” · Inserting typical values for the DM candidate and...

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