Ely Kovetz

The Observable Universe: probes of different epochs in its history.

What do I do?

For more details about my research, including links to relevant talks and publications, click on the topics below:

The Cosmic Microwave Background: Exploring the Early Universe

Line-Intensity Mapping: Astrophysics and Cosmology at High Redshifts

Gravitational waves from Mergers of Compact Objects: a Powerful New Probe

Why am I interested?

In recent celebrated work, my colleagues at JHU and I proposed that the GWs detected by LIGO originated from the coalescence of ~30 M⊙ primordial-BH (PBH) binaries which make up the dark matter. We found the rate of such mergers, dominated by eccentric events in low-mass dark matter halos, to be consistent with LIGO estimates for the merger rate of massive BHs.
How would we detect PBH dark matter?
As illustrated in the figure below (from Kovetz, PRL 2017), we can use an analogy with the detection methods of particle dark matter. Direct detection looks for signatures of direct interactions between standard astrophysical objects and PBHs. Indirect detection examines the signal from “annihilation” of two PBHs, i.e. gravitational waves. Direct detection: With J. Muñoz, a JHU graduate student at the time (now @Harvard), we proposed a general method to probe compact dark matter by studying Fast Radio Bursts (FRBs) with repeating echoes as a result of strong gravitational lensing by these compact sources, showing that tight bounds can be achieved in the ∼20−100M⊙ mass range with one year of CHIME observations. Future analysis of GRB autocorrelations may lead to even tighter constraints (Ji, Kovetz and Kamionkowski, 2018).
Indirect detection: As in the particle dark-matter case, the challenge is to quantify the standard model background and identify unique features of the desired signal. In Kovetz (PRL, 2017), I examined the indirect detection prospects with LIGO, taking into account the stellar-BH background. With JHU collaborators, we suggested to probe the progenitors of merging binaries based on the characteristically high orbital ellipticity in those formed by two-body capture. Finally, in recent work we considered the merger rate of early-Universe PBH binaries, estimating analytically the effects of interactions with baryons and other dark matter, and showed that LIGO may already place strong constraints on PBHs. Follow up work involves numerical simulations to verify this.

Left: Constraints on the fraction fDM of dark matter in PBHs in the LIGO mass window. Microlensing con- straints shown in cyan; from galactic wide binaries in red; from the lensing magnification PDF of SNe in blue; dynamical constraints from Eri II and ultra-faint dwarfs in green/yellow. Stronger limits are inferred from LIGO O1 results (Ali-Haımoud, Kovetz and Kamionkowski, 2017) and expected soon from null detection of strong lensing of FRBs in CHIME (Munoz, Kovetz et al., PRL 2016).
Right: Future constraints on the fraction of dark matter in PBHs, as a function of mass: Dashed lines correspond to 3σ limits, solid lines are more stringent 5σ limits. Constraints based on the 1D mass distribution shown in red; 2D distribution (tighter, as the noise per bin is smaller) in blue. For 30M⊙, we get fPBH 50% at 5σ (3σ) in the 2D (1D) case. Bands indicate factors 400% (200%) uncertainty in the background (signal) amplitude. From Kovetz (PRL, 2017).

Related talks:

In Kovetz et al. (2017), I explored how the BH mass function can be probed with LIGO, providing important insights regarding stellar-BH formation (such as the empirically motivated mass gap between Neutron Stars and BHs), progenitor scenarios for merging binaries, wind-driven mass-loss in Wolf-Rayet stars, etc. Based on the simplest assumptions for the stellar-BH mass function—an Initial Mass Function (α=−2.35) power-law and an exponential cutoff—our prediction (with half the data published at the time) for the distribution of detected mergers with BH masses M1,M2 agrees nicely with new data. The prescription we provided for estimating future measurement uncertainty in the mass function and merger rate parameters is being further developed and will enable to place constraints on more detailed modeling of the progenitors, taking into account star-formation history and metallicity evolution, isolated vs. dynamical binary formation, etc. In recent work with colleagues at JHU, we focused on probing hierarchical mergers in globular clusters (GCs) and the runaway formation of intermediate mass BHs with LIGO, showing how future LIGO measurements can set limits on their occupation fraction in GCs (with implications for their potential to provide supermassive BH (SMBH) seeds). Recent work (Wong, Kovetz et al., 2018) addressed the synergy between ground-based observatories and LISA, showing that information from the former can greatly boost the detection rate of stellar-mass BH mergers in the latter. Essentially, we demonstrated that the ground-based catalog of detected events can be used to filter out spurious noise triggers that show up as the detection threshold of LISA is lowered. We showed that this could yield as much as a factor 4-8 increase in the number of "multi-band" stellar-mass black-hole mergers - i.e., events detected in both a ground-based LIGO-type network and LISA. Multi-band detections (with larger frequency lever arm) will yield better measurements of eccentricity (crucial for distinguishing between binary-formation channels) and enable various tests of modified GR.

     Left: Predicted mass distributions of detected stellar-BH mergers (Kovetz et al. 2017) without (blue) and with (red) the inclusion of mergers from runaway formation of intermediate-mass black holes (Kovetz et al. 2018). Advanced LIGO will be able to probe this IMBH formation mechanism.
Right: Boost factor in LISA detection rate of stellar-mass BH mergers using ground-based information (Wong, Kovetz et al. 2018)

Related talks:

Odds and Ends