Detectability of microlensed gravitational waves Yeung, Simon M C; Cheung, Mark H Y; Seo, Eungwang ...
Monthly notices of the Royal Astronomical Society,
09/2023, Volume:
526, Issue:
2
Journal Article
Peer reviewed
ABSTRACT
Gravitational lensing describes the bending of the trajectories of light and gravitational waves due to the gravitational potential of a massive object. Strong lensing by galaxies can create ...multiple images with different overall amplifications, arrival times, and image types. If, furthermore, the gravitational wave encounters a star along its trajectory, microlensing will take place. Previously, it has been shown that the effects of microlenses on strongly-lensed type-I images could be negligible in practice, at least in the low magnification regime. In this work, we study the same effect on type-II strongly-lensed images by computing the microlensing amplification factor. As opposed to being magnified, type-II images are typically demagnified. Moreover, microlensing on top of type-II images induces larger mismatches with un-microlensed waveforms than type-I images. These results are broadly consistent with recent literature and serve to confirm the findings. In addition, we investigate the possibility of detecting and analysing microlensed signals through Bayesian parameter estimation with an isolated point mass lens template, which has been adopted in recent parameter estimation literature. In particular, we simulate gravitational waves microlensed by a microlens embedded in a galaxy potential near moderately magnified type-I and II macroimages, with variable lens masses, source parameters and macromagnifcations. Generally, an isolated point mass model could be used as an effective template to detect a type-II microlensed image but not for type-I images, demonstrating the necessity for more realistic microlensing search templates.
Stellar-mass microlensing of gravitational waves Cheung, Mark H Y; Gais, Joseph; Hannuksela, Otto A ...
Monthly notices of the Royal Astronomical Society,
05/2021, Volume:
503, Issue:
3
Journal Article
Peer reviewed
Open access
ABSTRACT
When gravitational waves (GWs) pass through the nuclear star clusters of galactic lenses, they may be microlensed by the stars. Such microlensing can cause potentially observable beating ...patterns on the waveform due to waveform superposition and magnify the signal. On the one hand, the beating patterns and magnification could lead to the first detection of a microlensed GW. On the other hand, microlensing introduces a systematic error in strong lensing use-cases, such as localization and cosmography studies. By numerically solving the lensing diffraction integral, we show that diffraction effects are important when we consider GWs in the LIGO frequency band lensed by objects with masses $\lesssim 100 \, \rm M_\odot$. We also show that the galaxy hosting the microlenses changes the lensing configuration qualitatively, so we cannot treat the microlenses as isolated point mass lenses when strong lensing is involved. We find that for stellar lenses with masses $\sim \! 1 \, \rm M_\odot$, diffraction effects significantly suppress the microlensing magnification. Thus, our results suggest that GWs lensed by typical galaxy or galaxy cluster lenses may offer a relatively clean environment to study the lens system, free of contamination by stellar lenses, which can be advantageous for localization and cosmography studies.
One class of competitive candidates for dark matter is ultralight bosons. If they exist, these bosons may form long-lived bosonic clouds surrounding rotating black holes via superradiant ...instabilities, acting as sources of gravity and affecting the propagation of gravitational waves around the host black hole. During extreme-mass-ratio inspirals, the bosonic clouds will survive the inspiral phase and can affect the quasinormal-mode frequencies of the perturbed black-hole–bosonic-cloud system. In this work, we compute the shifts of gravitational quasinormal-mode frequencies of a rotating black hole due to the presence of a surrounding bosonic cloud. We then perform a mock analysis on simulated Laser Interferometer Space Antenna observational data containing injected ringdown signals from supermassive black holes with and without a bosonic cloud. We find that with less than an hour of observational data of the ringdown phase of nearby supermassive black holes such as Sagittarius A* and M32, we can rule out or confirm the existence of cloud-forming ultralight bosons of mass ~ 10−17 eV .
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Abstract
The population properties of intermediate-mass black holes remain largely unknown, and understanding their distribution could provide a missing link in the formation of supermassive black ...holes and galaxies. Gravitational-wave observations can help fill in the gap from stellar mass black holes to supermassive black holes with masses between ∼100–10
4
M
⊙
. In our work, we propose a new method for examining lens populations through lensing statistics of gravitational waves, here focusing on inferring the number density of intermediate-mass black holes through hierarchical Bayesian inference. Simulating ∼200 lensed gravitational-wave signals, we find that existing gravitational-wave observatories at their design sensitivity could either constrain the number density of 10
6
Mpc
−3
within a factor of 10, or place an upper bound of ≲10
4
Mpc
−3
if the true number density is 10
3
Mpc
−3
. More broadly, our method leaves room for incorporation of additional lens populations, providing a general framework for probing the population properties of lenses in the universe.
Gravitational lensing describes the bending of the trajectories of light and gravitational waves due to the gravitational potential of a massive object. Strong lensing by galaxies can create multiple ...images with different overall amplifications, arrival times, and image types. If, furthermore, the gravitational wave encounters a star along its trajectory, microlensing will take place. Previously, it has been shown that the effects of microlenses on strongly-lensed type-I images could be negligible in practice, at least in the low magnification regime. In this work, we study the same effect on type-II strongly-lensed images by computing the microlensing amplification factor. As opposed to being magnified, type-II images are typically demagnified. Moreover, microlensing on top of type-II images induces larger mismatches with un-microlensed waveforms than type-I images. These results are broadly consistent with recent literature and serve to confirm the findings. In addition, we investigate the possibility of detecting and analysing microlensed signals through Bayesian parameter estimation with an isolated point mass lens template, which has been adopted in recent parameter estimation literature. In particular, we simulate gravitational waves microlensed by a microlens embedded in a galaxy potential near moderately magnified type-I and II macroimages, with variable lens masses, source parameters and macromagnifcations. Generally, an isolated point mass model could be used as an effective template to detect a type-II microlensed image but not for type-I images, demonstrating the necessity for more realistic microlensing search templates.
Abstract
Solving the problem of dark matter remains one of the greatest unsolved mystery of fundamental physics. One possible dark matter candidate is the scalar ultralight boson, with mass « 1eV. If ...they exist, ultralight bosons will form clouds of significant total mass about rotating black holes, affecting the spacetime around the black hole. After the inspiral phase of a binary merger, the bosonic cloud can affect the perturbations to the black hole, resulting in deviations in the quasinormal mode frequencies of the ringdown signal of a binary merger. Here, we compute these shifts in the gravitational quasinormal mode frequencies for such a system, and conduct an injection campaign with supermassive black holes detected by the Laser Interferometer Space Antenna. We find that detections of the ringdown phase of supermassive black holes can rule out or confirm the existence of cloud-forming ultralight bosons of mass ∼ 10
−18
eV at redshift
z
> 1 if cloud dissipation effects during the inspiral can be neglected.
The population properties of intermediate mass black holes remain largely unknown, and understanding their distribution could provide a missing link in the formation of supermassive black holes and ...galaxies. Gravitational wave observations can help fill in the gap from stellar mass black holes to supermassive black holes. In our work, we propose a new method for probing lens populations through lensing statistics of gravitational waves, here focusing on inferring the number density of intermediate mass black holes. Using hierarchical Bayesian inference of injected lensed gravitational waves, we find that existing gravitational wave observatories at design sensitivity could either identify an injected number density of \(10^6 \mathrm{Mpc}^{-3}\) or place an upper bound of \(\lesssim 10^4 \mathrm{Mpc}^{-3}\) for an injected \(10^3 \mathrm{Mpc}^{-3}\). More broadly, our method could be applied to probe other forms of compact matter as well.
One class of competitive candidates for dark matter is ultralight bosons. If they exist, these bosons may form long-lived bosonic clouds surrounding rotating black holes via superradiant ...instabilities, acting as sources of gravity and affecting the propagation of gravitational waves around the host black hole. During extreme-mass-ratio inspirals, the bosonic clouds will survive the inspiral phase and can affect the quasinormal-mode frequencies of the perturbed black-hole-bosonic-cloud system. In this work, we compute the shifts of gravitational quasinormal-mode frequencies of a rotating black hole due to the presence of a surrounding bosonic cloud. We then perform a mock analysis on simulated Laser Interferometer Space Antenna observational data containing injected ringdown signals from supermassive black holes with and without a bosonic cloud. We find that with less than an hour of observational data of the ringdown phase of nearby supermassive black holes such as Sagittarius A* and M32, we can rule out or confirm the existence of cloud-forming ultralight bosons of mass \( \sim 10^{-17} \rm eV\).
When gravitational waves pass through the nuclear star clusters of galactic lenses, they may be microlensed by the stars. Such microlensing can cause potentially observable beating patterns on the ...waveform due to waveform superposition and magnify the signal. On the one hand, the beating patterns and magnification could lead to the first detection of a microlensed gravitational wave. On the other hand, microlensing introduces a systematic error in strong lensing use-cases, such as localization and cosmography studies. We show that diffraction effects are important when we consider GWs in the LIGO frequency band lensed by objects with masses \(\lesssim 100 \, \rm M_\odot\). We also show that the galaxy hosting the microlenses changes the lensing configuration qualitatively, so we cannot treat the microlenses as isolated point mass lenses when strong lensing is involved. We find that for stellar lenses with masses \(\sim 1 \, \rm M_\odot\), diffraction effects significantly suppress the microlensing magnification. Thus, our results suggest that gravitational waves lensed by typical galaxy or galaxy cluster lenses may offer a relatively clean environment to study the lens system, free of contamination by stellar lenses. We discuss potential implications for the strong lensing science case. More complicated microlensing configurations will require further study.
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