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

22 August 2007COSMO 07, Univ. Sussex2 The overall gist Primordial black holes (PBHs) may have formed in the early universe Primordial black holes (PBHs) may have formed in the early universe Evaporation of PBHs injects energy into the intergalactic medium Evaporation of PBHs injects energy into the intergalactic medium Energy injection affects ionization and temperature of IGM Energy injection affects ionization and temperature of IGM The redshifted 21cm line of neutral hydrogen is sensitive to changes in both – very good probe of exotic physics The redshifted 21cm line of neutral hydrogen is sensitive to changes in both – very good probe of exotic physics

22 August 2007COSMO 07, Univ. Sussex3

22 August 2007COSMO 07, Univ. Sussex4

22 August 2007COSMO 07, Univ. Sussex5 21cm signal During Dark Ages, universe mostly cold neutral hydrogen, and visible/UV light immediately absorbed During Dark Ages, universe mostly cold neutral hydrogen, and visible/UV light immediately absorbed Use the hyperfine splitting line of hydrogen: Use the hyperfine splitting line of hydrogen: in radio wavelengths, unabsorbed in radio wavelengths, unabsorbed requires little energy to excite requires little energy to excite

22 August 2007COSMO 07, Univ. Sussex6 21cm tomography z=8.16z=7.68z=6.89 Zahn et al 2006

22 August 2007COSMO 07, Univ. Sussex7 Observing with 21cm

22 August 2007COSMO 07, Univ. Sussex8 21cm vs. CMB More information in 21cm tomography More information in 21cm tomography temperature + ionization of gas temperature + ionization of gas many redshifts (not an integrated signal) many redshifts (not an integrated signal) Example: constraining dark matter annihilation (measuring energy injection) Example: constraining dark matter annihilation (measuring energy injection) CMBPol: (dE/dt)/vol < eV/s/m 3 (Padmanabhan & Finkbeiner 2005) CMBPol: (dE/dt)/vol < eV/s/m 3 (Padmanabhan & Finkbeiner 2005) Future 21cm obs: (dE/dt)/vol < eV/s/m 3 (Furlanetto, Oh & Pierpaoli 2006) Future 21cm obs: (dE/dt)/vol < eV/s/m 3 (Furlanetto, Oh & Pierpaoli 2006)

22 August 2007COSMO 07, Univ. Sussex9 Spin and brightness temps The 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

22 August 2007COSMO 07, Univ. Sussex10 z=200z=30 Temperature atomic collisions Radiative coupling to CMB Wouthuysen-Field Effect X-ray heating TγTγ Spin and brightness temps

22 August 2007COSMO 07, Univ. Sussex11 Hawking radiation PBHs emit particles in a roughly blackbody spectral distribution PBHs emit particles in a roughly blackbody spectral distribution Temperature ~ M -1 Temperature ~ M -1 Power ~ M -2 Power ~ M -2 Lifetime ~ M 3 Lifetime ~ M 3 PBH evaporation injects energy into the IGM PBH evaporation injects energy into the IGM

22 August 2007COSMO 07, Univ. Sussex12 Analogy with decaying dark matter Furlanetto, Oh & Pierpaoli (hereafter FOP) Furlanetto, Oh & Pierpaoli (hereafter FOP) Energy injection from decaying DM in the dark ages Energy injection from decaying DM in the dark ages Implications for 21cm observations Implications for 21cm observations Claim: 21cm can detect eV/cm 3 /s Claim: 21cm can detect eV/cm 3 /s Hypothesis: PBH evaporation should look similar to decaying DM Hypothesis: PBH evaporation should look similar to decaying DM

22 August 2007COSMO 07, Univ. Sussex13 Simple order-of-magnitude estimate Assume: Assume: Constant comoving number density n PBH Constant comoving number density n PBH Uniformly distributed PBHs Uniformly distributed PBHs Constant energy injection rate Constant energy injection rate Find (dE/dt)/volume for M=10 11 kg PBHs: Find (dE/dt)/volume for M=10 11 kg PBHs: P ͌ 2e-4 * hbar * c 6 / (G * M) 2 = 3.4e11 W Limit: eV/cm 3 /s = 1.6e-37 J/m 3 /s => n PBH Ω PBH n PBH Ω PBH < 4.7e-12

22 August 2007COSMO 07, Univ. Sussex14 Method

22 August 2007COSMO 07, Univ. Sussex15 Method 1.Simulate Hawking radiation Produce spectrum (with graybody factors) Produce spectrum (with graybody factors) Track photon energies with redshift Track photon energies with redshift 2. 2.Allow for absorption by IGM photoionization, Compton scattering, pair production (off atoms, free ions and the CMB), scattering off CMB photons 3. 3.Find total energy injection into IGM over course of PBH evolution 4. 4.Track temperature and ionization of IGM (pre- and post-recombination) 5. 5.Track 21cm brightness temperature 6. 6.Compute 21cm power spectrum

22 August 2007COSMO 07, Univ. Sussex16 Method 1.Simulate Hawking radiation Produce spectrum (with graybody factors) Produce spectrum (with graybody factors) Track photon energies with redshift Track 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 photoionization, Compton scattering, pair production (off atoms, free ions and the CMB), scattering off CMB photons 3. 3.Find total energy injection into IGM over course of PBH evolution 4. 4.Track temperature and ionization of IGM (pre- and post-recombination) 5. 5.Track 21cm brightness temperature 6. 6.Compute 21cm power spectrum

22 August 2007COSMO 07, Univ. Sussex17 Method 1.Simulate Hawking radiation Produce spectrum (with graybody factors) Produce spectrum (with graybody factors) Track photon energies with redshift Track 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 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. 4.Track temperature and ionization of IGM (pre- and post-recombination) 5. 5.Track 21cm brightness temperature 6. 6.Compute 21cm power spectrum

22 August 2007COSMO 07, Univ. Sussex18 Method 1.Simulate Hawking radiation Produce spectrum (with graybody factors) Produce spectrum (with graybody factors) Track photon energies with redshift Track 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 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. 5.Track 21cm brightness temperature 6. 6.Compute 21cm power spectrum

22 August 2007COSMO 07, Univ. Sussex19 Method 1.Simulate Hawking radiation Produce spectrum (with graybody factors) Produce spectrum (with graybody factors) Track photon energies with redshift Track 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 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 temperature 6. 6.Compute 21cm power spectrum

22 August 2007COSMO 07, Univ. Sussex20 Method 1.Simulate Hawking radiation Produce spectrum (with graybody factors) Produce spectrum (with graybody factors) Track photon energies with redshift Track 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 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 temperature 6.Compute 21cm power spectrum

22 August 2007COSMO 07, Univ. Sussex21 Results – ionization history PBHs and decaying DM

22 August 2007COSMO 07, Univ. Sussex22 Results – ionization history late-evaporating PBHs

22 August 2007COSMO 07, Univ. Sussex23 Results – ionization history early-evaporating PBHs

22 August 2007COSMO 07, Univ. Sussex24 Results – ionization history M = kg, z evap = 22 M = 5 x kg, z evap = 89 early-evaporating PBHs

22 August 2007COSMO 07, Univ. Sussex25 Results – brightness temperature (no energy injection)

22 August 2007COSMO 07, Univ. Sussex26 Results – brightness temperature (no energy injection) M = 5 x kg z evap = 89 M = kg, z evap = 22

22 August 2007COSMO 07, Univ. Sussex27 Conclusions & future work 21cm observations can detect exotic sources of energy injection in the dark ages 21cm observations can detect exotic sources of energy injection in the dark ages Limits on PBH evaporation from 21cm will be at least comparable to existing limits Limits on PBH evaporation from 21cm will be at least comparable to existing limits Future work: Future work: 21cm power spectrum calculation 21cm power spectrum calculation Predict constraints given survey parameters Predict constraints given survey parameters Use 21cm for other exotic physics Use 21cm for other exotic physics