Primordial Black Holes in the Dark Ages Katie Mack (Princeton/Cambridge) with Daniel Wesley (DAMTP Cambridge)

Primordial Black Holes in Primordial Black Holes in the Dark Agesthe Dark Ages

Katie Mack Katie Mack (Princeton/Cambridge)(Princeton/Cambridge)

with Daniel Wesley (DAMTP Cambridge)with Daniel Wesley (DAMTP Cambridge)

22 August 200722 August 2007 COSMO 07, Univ. SussexCOSMO 07, Univ. Sussex 22

The overall gistThe overall gist

Primordial black holesPrimordial black holes (PBHs) may have (PBHs) may have formed in the early universeformed in the early universe

Evaporation of PBHs Evaporation of PBHs injects energyinjects energy into into the intergalactic mediumthe intergalactic medium

Energy injection affects Energy injection affects ionization and ionization and temperature of IGMtemperature of IGM

The redshifted The redshifted 21cm21cm line of neutral line of neutral hydrogen is sensitive to changes in both – hydrogen is sensitive to changes in both – very good probe of exotic physicsvery good probe of exotic physics




21cm signal21cm signal

During Dark Ages, universe mostly During Dark Ages, universe mostly cold neutral hydrogen, and visible/UV cold neutral hydrogen, and visible/UV light immediately absorbedlight immediately absorbed

Use the hyperfine splitting line of Use the hyperfine splitting line of hydrogen:hydrogen: in radio wavelengths, unabsorbedin radio wavelengths, unabsorbed requires little energy to exciterequires little energy to excite


21cm tomography21cm tomography

z=8.16 z=7.68 z=6.89

Zahn et al 2006


Observing with 21cmObserving with 21cm


21cm vs. CMB21cm vs. CMB

More information in 21cm tomographyMore information in 21cm tomography temperature + ionization of gastemperature + ionization of gas many redshifts (not an integrated signal)many redshifts (not an integrated signal)

Example: constraining dark matter Example: constraining dark matter annihilation (measuring energy injection)annihilation (measuring energy injection) CMBPol: (dE/dt)/vol < 10CMBPol: (dE/dt)/vol < 10-16-16 eV/s/m eV/s/m33

(Padmanabhan & Finkbeiner 2005)(Padmanabhan & Finkbeiner 2005) Future 21cm obs: (dE/dt)/vol < 10Future 21cm obs: (dE/dt)/vol < 10-18-18 eV/s/m eV/s/m33

(Furlanetto, Oh & Pierpaoli 2006)(Furlanetto, Oh & Pierpaoli 2006)


Spin and brightness tempsSpin and brightness tempsThe spin temperature determines the relative occupancy of the hyperfine levels

The brightness temperature measured by observations is determined by the spin temperature’s coupling to the CMB


z=200z=30

Tk

Ts

Temperature

atomic collisions

Radiative coupling to CMB

Wouthuysen-Field Effect

X-ray heatingTγ

Spin and brightness tempsSpin and brightness temps


Hawking radiationHawking radiation

PBHs emit particles PBHs emit particles in a roughly in a roughly blackbody spectral blackbody spectral distributiondistribution

Temperature ~ MTemperature ~ M-1-1

Power ~ MPower ~ M-2-2

Lifetime ~ MLifetime ~ M33

PBH evaporation PBH evaporation injects energy into injects energy into the IGMthe IGM


Analogy with decaying dark Analogy with decaying dark mattermatter

Furlanetto, Oh & Pierpaoli (hereafter FOP)Furlanetto, Oh & Pierpaoli (hereafter FOP) Energy injection from decaying DM in the dark agesEnergy injection from decaying DM in the dark ages Implications for 21cm observationsImplications for 21cm observations

Claim: 21cm can detect Claim: 21cm can detect 1010-24-24 eV/cm eV/cm33/s/s Hypothesis: PBH evaporation should look similar Hypothesis: PBH evaporation should look similar

to decaying DMto decaying DM


Simple order-of-magnitude Simple order-of-magnitude estimateestimate

Assume:Assume: Constant comoving number density nConstant comoving number density nPBHPBH

Uniformly distributed PBHsUniformly distributed PBHs Constant energy injection rateConstant energy injection rate

Find (dE/dt)/volume for M=10Find (dE/dt)/volume for M=101111 kg PBHs: kg PBHs:

PP ͌͌ 2e-4 * hbar * c2e-4 * hbar * c66 / (G * M) / (G * M)22 = 3.4e11 W = 3.4e11 W

Limit: 10Limit: 10-24-24 eV/cm eV/cm33/s = 1.6e-37 J/m/s = 1.6e-37 J/m33/s/s

=>=> n nPBHPBH < 4.7e-49 m < 4.7e-49 m-3-3 =>=> ΩΩPBHPBH < 4.7e-12 < 4.7e-12


MethodMethod


MethodMethod1.1. Simulate Simulate Hawking radiationHawking radiation

Produce spectrum (with graybody factors)Produce spectrum (with graybody factors) Track photon energies with redshiftTrack photon energies with redshift

2. Allow for absorption by IGM photoionization, Compton scattering, pair

production (off atoms, free ions and the CMB), scattering off CMB photons

3. Find total energy injection into IGM over course of PBH evolution

4. Track temperature and ionization of IGM (pre- and post-recombination)

5. Track 21cm brightness temperature6. Compute 21cm power spectrum




2.2. Allow for Allow for absorptionabsorption by IGM by IGM photoionization, Compton scattering, pair photoionization, Compton scattering, pair

production (off atoms, free ions and the production (off atoms, free ions and the CMB), scattering off CMB photonsCMB), scattering off CMB photons

3. Find total energy injection into IGM over course of PBH evolution








3.3. Find Find total energy injectiontotal energy injection into IGM over into IGM over course of PBH evolutioncourse of PBH evolution









4.4. Track Track temperaturetemperature and and ionizationionization of IGM of IGM (pre- and post-recombination)(pre- and post-recombination)









5.5. Track 21cm Track 21cm brightness temperaturebrightness temperature6. Compute 21cm power spectrum








5.5. Track 21cm Track 21cm brightness temperaturebrightness temperature6.6. Compute Compute 21cm power spectrum21cm power spectrum


Results – ionization historyResults – ionization historyPBHs and decaying DM


Results – ionization historyResults – ionization historylate-evaporating PBHs


Results – ionization historyResults – ionization historyearly-evaporating PBHs


Results – ionization historyResults – ionization history

M = 1011 kg, z evap

= 22

M = 5 x 1010 kg, z evap

= 89

early-evaporating PBHs


Results – brightness Results – brightness temperaturetemperature

(no energy injection)


Results – brightness Results – brightness temperaturetemperature

(no energy injection)

M = 5 x 1010 kg

z evap = 89

M = 1011 kg, zevap = 22


Conclusions & future workConclusions & future work

21cm observations can detect exotic 21cm observations can detect exotic sources of energy injection in the dark sources of energy injection in the dark agesages

Limits on PBH evaporation from 21cm Limits on PBH evaporation from 21cm will be at least comparable to existing will be at least comparable to existing limitslimits

Future work:Future work: 21cm power spectrum calculation21cm power spectrum calculation Predict constraints given survey parametersPredict constraints given survey parameters Use 21cm for other exotic physicsUse 21cm for other exotic physics

Documents

Primordial Black Holes in the Dark Ages Katie Mack (Princeton/Cambridge) with Daniel Wesley (DAMTP Cambridge)