2021ApJ...912...53W

Due to their small mass, subsolar mass black hole binaries would have to be primordial in origin instead of the result of stellar evolution. Soon after formation in the early universe, primordial black holes can form binaries after decoupling from the cosmic expansion. Alternatively, primordial black holes as dark matter could also form binaries in the late universe due to dynamical encounters and gravitational-wave braking. A significant feature for this channel is the possibility that some sources retain nonzero eccentricity in the LIGO/Virgo band. Assuming all dark matter is primordial black holes with a delta function mass distribution, 1M_☉-1M_☉ binaries formed in this late-universe channel can be detected by Advanced LIGO and Virgo with their design sensitivities at a rate of O (1) yr^–1, where 12%(3%) of events have eccentricity at a gravitational-wave frequency of 10 Hz, e^10 Hz^ >= 0.01(0.1), and nondetection can constrain the binary formation rate within this model. Third generation detectors would be expected to detect subsolar mass eccentric binaries as light as 0.01M_☉ within this channel, if they accounted for the majority of the dark matter. Furthermore, we use simulated gravitational-wave data to study the ability to search for eccentric gravitational-wave signals using a quasi-circular waveform template bank with Advanced LIGO design sensitivity. For a match-filtering targeted search, assuming binaries with a delta function mass of 0.1(1)M_☉ and the eccentricity distribution derived from this late-universe formation channel, 41%(6%) of the signals would be missed compared to the ideal detection rate due to the mismatch in the gravitational-wave signal from eccentricity.