[Paper Review] Electromagnetic probes of primordial black holes as dark matter

Yacine Ali-Haïmoud, S. Clesse+92 more|arXiv (Cornell University)|Mar 11, 2019

Pulsars and Gravitational Waves Research106 references21 citations

TL;DR

This paper proposes that electromagnetic observations from upcoming 2020s missions—Euclid, WFIRST, eROSITA, and Athena—can probe whether primordial black holes (PBHs) with masses ~30 M⊙ constitute all or part of dark matter. By measuring sub-percent-level fluctuations in the source-subtracted cosmic infrared background and cross-correlating them with unresolved X-ray background anisotropies, the method can test PBH dark matter models with high sensitivity, offering a critical electromagnetic pathway to confirm or rule out this long-standing hypothesis.

ABSTRACT

The LIGO discoveries have rekindled suggestions that primordial black holes (BHs) may constitute part to all of the dark matter (DM) in the Universe. Such suggestions came from 1) the observed merger rate of the BHs, 2) their unusual masses, 3) their low/zero spins, and 4) also from the independently uncovered cosmic infrared background (CIB) fluctuations signal of high amplitude and coherence with unresolved cosmic X-ray background (CXB). Here we summarize the prospects to resolve this important issue with electromagnetic observations using the instruments and tools expected in the 2020's. These prospects appear promising to make significant, and potentially critical, advances. We demonstrate that in the next decade, new space- and ground-borne electromagnetic instruments, combined with concurrent theoretical efforts, should shed critical light on the long-considered link between primordial BHs and DM. Specifically the new data and methodologies under this program will involve: I) Probing with high precision the spatial spectrum of source-subtracted CIB with Euclid and WFIRST, and its coherence with unresolved cosmic X-ray background using eROSITA and Athena, II) Advanced searches for microlensing of Galactic stars by the intervening Galactic Halo BHs with OGLE, Gaia, LSST and WFIRST, III) Supernovae (SNe) lensing in the upcoming surveys with WFIRST, LSST and also potentially with Euclid and JWST, IV) Advanced theoretical work to understand the details of PBH accretion and evolution and their influence on cosmic microwave background (CMB) anisotropies in light of the next generation CMB experiments, V) Better new samples and theoretical understanding involving stability and properties of ultra faint dwarf galaxies, pulsar timing, and cosmological quasar lensing.

Motivation & Objective

• To test the hypothesis that primordial black holes (PBHs) with ~30 M⊙ masses constitute all or part of the dark matter in the Universe.
• To leverage upcoming 2020s space and ground-based electromagnetic instruments to resolve the PBH-dark matter connection with high precision.
• To use cross-correlation of cosmic infrared background (CIB) and unresolved cosmic X-ray background (CXB) fluctuations to detect PBH-induced anisotropies.
• To advance theoretical understanding of PBH accretion, evolution, and their imprints on CMB anisotropies and galaxy populations.
• To combine microlensing surveys (OGLE, Gaia, LSST, WFIRST) and quasar lensing data to constrain PBH mass functions and halo distributions.

Proposed method

• Measure source-subtracted cosmic infrared background (CIB) anisotropies at 1.8 μm with Euclid and WFIRST to sub-percent statistical accuracy.
• Cross-correlate CIB fluctuations with unresolved cosmic X-ray background (CXB) using eROSITA and Athena to detect coherence indicative of high-redshift PBHs.
• Model the CIB power spectrum as a Poissonian granulation component from unresolved 30 M⊙ PBHs, comparing it to the ΛCDM baseline.
• Use microlensing light curves from OGLE, Gaia, LSST, and WFIRST to detect PBHs in the Galactic halo via amplification of stellar sources.
• Analyze supernova lensing signatures in deep surveys from WFIRST, LSST, and Euclid to constrain PBH abundance and mass function.
• Integrate theoretical models of PBH accretion and evolution with predictions for CMB anisotropy distortions, informed by next-generation CMB experiments.

Experimental results

Research questions

• RQ1 Can the coherence between source-subtracted CIB anisotropies and the unresolved CXB fluctuation at high redshift provide evidence for PBHs as dark matter?
• RQ2 To what extent can sub-percent-level measurements of CIB fluctuations with Euclid distinguish a PBH-like model from known galaxy populations?
• RQ3 How do microlensing surveys with OGLE, Gaia, and LSST constrain the fraction of dark matter in PBHs across different mass ranges?
• RQ4 Can supernova lensing surveys with WFIRST and LSST detect PBH-induced magnification effects consistent with PBH dark matter models?
• RQ5 What are the predicted imprints of PBH accretion on CMB anisotropies, and how can next-generation CMB experiments test these predictions?

Key findings

• The reconstructed CXB fluctuation from CIB sources is consistent with a high-redshift origin, at levels not directly detectable by future X-ray missions, suggesting a hidden component like PBHs.
• The Poissonian granulation component from 30 M⊙ PBHs making up dark matter closely matches the observed CIB power spectrum, providing a strong consistency check.
• Euclid is expected to measure source-subtracted CIB fluctuations at 1.8 μm with sub-percent statistical accuracy, enabling a direct test of PBH models against known galaxy populations.
• CIB-CXB cross-power measurements using Euclid and eROSITA (green) or Athena (red) can recover the CXB signal at high significance, offering a clean probe of unresolved PBHs.
• Microlensing surveys with OGLE, Gaia, LSST, and WFIRST are expected to detect PBHs in the Galactic halo with high sensitivity, particularly for masses around 30 M⊙.
• Theoretical modeling of PBH accretion and CMB anisotropy effects, combined with next-gen CMB experiments, will further constrain PBH dark matter scenarios.