arXiv subjects

Kelly Holley-Bockelmann

Publications and source records attributed to Kelly Holley-Bockelmann.

At least 19 recordsLinked to original sources

arXiv2026

Formation of a nuclear star cluster through the inspiral of globular clusters: A case study of the dwarf elliptical galaxy UGC 7346

Nuclear star clusters (NSCs) are dense stellar environments located in the center of most galaxies. NSCs are thought to form through two primary methods; through the inspiral of globular clusters (GCs) to the galactic center due to dynamical friction, and through in-situ star formation. Recent observations of dwarf elliptical galaxy UGC 7346 suggest that it might be undergoing NSC formation due to the presence of multiple GCs near its photometric center. We perform direct N-body simulations of nine GCs belonging to UGC 7346's GC system to investigate whether their eventual infall to the galactic center would result in the formation of a NSC. Our simulations indicate that GC inspiral leads to the formation of a central stellar over-density relative to the background profile of the host galaxy within $\sim$1.5 Gyr, corresponding to a NSC with a typical mass of $(4.1\text{-}4.5)\times 10^5 M_{\odot}$. Several key structural parameters of the newly formed NSC, including the Sérsic index, effective radius, and central stellar density, lie well within the range observed for NSCs. We also test a hypothetical scenario in which some of the infalling GCs have larger masses ($M \sim 10^6 M_{\odot}$), resulting in the formation of a more massive NSC whose mass and size are more consistent with observations. Our results suggest that inspiral of GCs is a viable channel for assembling a significant mass in the shape of NSC in the center of dwarf galaxies and that UGC 7346 will host a NSC at its center in about 2-3 Gyr.

astro-ph.GA↗

arXiv2026

Probing the Nature of Dark Matter Self-Interactions Through Observations of Massive Black Hole Mergers

Though the nature of dark matter remains elusive, two models have come to prominence with testable predictions: cold dark matter (CDM) and self-interacting dark matter (SIDM). While CDM remains the widely accepted model, SIDM was introduced to potentially help resolve the discrepancies between the predictions of the CDM model and observational data, in particular the predicted central density profiles. Previous work involving simulations of small numbers of Milky Way-mass galaxies shows that SIDM with a constant cross section of 1 $\rm{cm^2/g}$ delays massive black hole (MBH) mergers as compared to CDM when the host halo has a flattened central density profile. In this work, we use mock gravitational wave observations of MBH mergers to test LISA's capability to indirectly probe dark matter physics. As a proof of concept, we use zoom-in simulations of two galaxy evolutionary histories to show that LISA may be able to distinguish (with a p--value $\leq$ 0.05) between CDM and SIDM with a short-range interaction and a constant cross section of 1 $\rm{cm^2/g}$, provided at least $\sim70$ MBH mergers are observed with signal-to-noise ratios greater than 10. Given our small sample size, this should be regarded as illustrative, rather than definitive. We emphasize that our work does not consider more realistic models with a velocity-dependent cross section, though our exploratory work shows that LISA may provide a pathway to probe dark matter self-interactions, motivating future work with more realistic, currently-favored models and larger simulation suites.

astro-ph.CO↗

arXiv2026

ArchGEM: an Advanced Data Analysis Tool for Analyzing Scattered Light Noise in LIGO

Scattered light is one of the most common sources of non-stationary noise at low frequencies in Advanced LIGO detectors. It appears as arch-like features in time-frequency spectrograms, produced when stray light reflects from moving surfaces and recombines with the main interferometer beam. In this study, we present ArchGEM, an automated framework for identifying and characterizing these arches and recovering the physical properties of the scattering surfaces. ArchGEM combines a prominence-based peak-finding method with a Gaussian Mixture Model clustering approach to capture a range of scattered-light morphologies across different detector conditions. We apply ArchGEM to scattered light glitches across Advanced LIGO observing runs O3 (2019--2020) and O4 (2023--2024). We find that the average frequency distributions of this noise span 15--25 Hz in O3a and O4, but increase to 20--40 Hz during O3b. Typical inferred surface velocities are 0.2--0.5 $μ$m/s, and inferred surface displacements are 0.1--0.3 $μ$m. The Gaussian Mixture Model performs most consistently for complex or overlapping features, with mean frequency offsets within 5 Hz of the Gravity Spy baseline. Our results show that ArchGEM provides a practical tool for detector characterization by linking observed spectrogram features to the motion of scattering surfaces and helping guide future mitigation of scattered light noise in current and next-generation interferometers. By quantifying the temporal and spectral behavior of scattered light, ArchGEM provides a robust framework for diagnosing noise sources and guiding targeted mitigation strategies in future detector upgrades.

astro-ph.IM↗

arXiv2026

Partial Relief of the Hubble Tension and a Natural Self-Interacting Dark Matter Candidate From Staged Symmetry Breaking

The values of the Hubble constant ($\rm{H_0}$) inferred from the cosmic microwave background (CMB) and local measurements via the distance ladder exhibit a $\sim5σ$ tension. In this work we propose that the tension might be partially alleviated if a subcomponent of the dark matter undergoes decays triggered by spontaneous symmetry breaking in the dark sector, so that the equation of state parameter of the subcomponent shifts from $w \approx 0$ at early times to $w \approx -1/3$ at late times. We provide an effective field theory whose structure is partially motivated by the desire for a plausible UV completion. We find that such a construction naturally produces a possible self-interacting dark matter candidate with a velocity-dependent scattering cross section as a by-product of gauge invariance. This is relevant for addressing tensions between the predictions of $Λ$CDM and observations of small-scale structure, such as the core-cusp problem.

astro-ph.CO↗

arXiv2025

Intermediate Mass Black Hole Binary Evolution in Nuclear Star Clusters: the effect of the stellar mass black hole population

In this study, we investigate the dynamics of Intermediate-Mass Black Hole (IMBH) binaries within Nuclear Star Clusters (NSCs) that contain a population of stellar-mass black holes (BHs). We examine how these stellar and BH populations influence the dynamics of the IMBH binary and, in turn, how the evolving IMBH binary affects the surrounding stellar and BH populations. We conduct high-resolution $N$-body simulations of NSCs constructed based on observational parameters from two local dwarf galaxies: NGC205 and NGC404. For the first time, we achieve a star particle mass resolution of $1\rm\;M_{\odot}$ and a BH mass resolution of $10\rm\;M_{\odot}$. This level of resolution is crucial for accurately modeling the collisional dynamics of these dense systems. Including stellar-mass BHs within the stellar population significantly influences the IMBH binary dynamics, nearly doubling the sinking rate and halving the merger time. During the initial phase of the inspiral, the IMBH binary disrupts both the stellar and BH cusps. However, the BH cusp quickly regains its steep slope due to its shorter relaxation time and continues to dominate the evolution of the IMBH binary, despite being much less massive compared to the stellar component. We uncover an interesting mechanism in which BHs first efficiently extract energy from the IMBH binary and then transfer this energy to the surrounding stars, allowing the BHs to spiral back toward the center of the system and restart the process. Our results imply that, although stellar mass BHs are a minor component of a stellar population, they can significantly facilitate IMBH growth within NSCs via mergers. We also notice that these dense systems can potentially boost Intermediate Mass Ratio Inspirals (IMRIs) predominantly on radial orbits.

astro-ph.GA↗

arXiv2025

DESI-Like Hubble Expansion From Staged Symmetry Breaking

The Dark Energy Spectroscopic Instrument (DESI) second data release shows a moderate preference for dark energy with a time-varying equation of state parameter, suggesting that the standard $Λ$CDM model may need to be revised. In particular, DESI favors dark energy whose equation of state parameter can drop below $-1$, violating the null energy condition. Chen and Loeb have recently suggested that this violation may be avoided if a subcomponent of the dark matter possesses a time-dependent equation of state. In this work, we present a realization of that idea which can be regarded as a more natural effective field theory. We show that such a construction not only yields dark matter with a time-varying equation of state parameter, but also naturally produces a self-interacting dark matter candidate with a velocity-dependent cross section as a consequence of gauge invariance. The second feature is relevant for addressing tensions between $Λ$CDM and observations of small-scale structure, particularly the diversity of galactic rotation curves.

astro-ph.CO↗

arXiv2025

Cosmological Impacts of Black Hole Mergers: No Relief in Sight for the Hubble Tension

The values of the Hubble constant inferred from local measurements and the cosmic microwave background (CMB) exhibit an approximately 5 sigma tension. Some have suggested this tension is alleviated if matter is converted to dark radiation via dark matter decay. As it is not clear that dark matter decays, we instead examine the effects of converting matter to gravitational radiation via black hole mergers. We consider mergers of supermassive black holes (SMBHs), mergers of stellar-mass black holes, and the formation of SMBHs from mergers of smaller black holes. We find that these processes cannot alleviate the tension, as an unrealistically large merger rate, or an overproduction of SMBHs is required. We also consider whether one can use the Integrated Sachs-Wolfe effect to constrain mechanisms that form SMBHs from mergers of smaller black holes. We find that this is also too small to be viable.

astro-ph.CO↗

arXiv2025

Probing Binary Black Hole Formation Channels through Cosmic Large-Scale Structure

The growing number of binary black hole mergers detected through gravitational waves offers unprecedented insight into their underlying population, yet their astrophysical formation channels remain unresolved. We present a new method to distinguish binary black hole formation channels using their spatial clustering at cosmological scales. Employing the cosmological hydrodynamic simulation Illustris, we trace the distribution of mergers across cosmic time and compare them with the underlying matter distribution associated with three candidate origins: isolated binary stellar evolution, binaries embedded in AGN disks, and primordial black holes within dark matter halos. For mergers at redshift $z \lesssim 0.5$, these channels show distinct clustering signatures that could be accessible with proposed upgrades to current ground-based gravitational-wave detectors. Using mock catalogs for next- generation facilities such as Cosmic Explorer, we find that their sensitivities would enable differentiation of these formation pathways out to redshift $z \sim 5$ within the first decade of observations. This approach provides a new framework to link gravitational-wave populations with the large-scale structure of the Universe. By treating black hole mergers as cosmological tracers, our results demonstrate how cross- correlations between gravitational-wave catalogs and the cosmic matter field can constrain the relative contribution of stellar, AGN, and primordial channels, offering a complementary probe to population- inference studies. These findings underscore the emerging potential of gravitational-wave cosmology to reveal where and how black holes form and merge across cosmic history.

gr-qc↗

arXiv2025

Handy Relation Between Binary Black Hole Merger Times and Host Galaxy Properties

Over the past 15 years, the evidence has clearly demonstrated that massive black hole (MBH) binary merger timescales depend strongly on the structural and kinematic properties of their host galaxy. Stellar density, gas content, shape and kinematics all play a role, combining in non-linear ways to effect the evolution of the binary. The binary properties themselves, such as eccentricity, mass ratio, and orbital plane, all matter as well. This makes it nontrivial to estimate accurate cosmological MBH binary merger rates, or to generate merger rate ranges that reflect the distribution of galaxy hosts and orbits. Using an extensive set of high-resolution direct N-body simulations in which the shape, structure, and kinematics of each galaxy host are directly informed by observations, we map out MBH binary merger timescales over a range of galaxy hosts and MBH binary orbits. This yields a convenient set of scaling relations to determine MBH binary merger timescales -- and the range of merger timescales -- as functions of basic observables. Such scaling relations can be readily employed as a subgrid model in cosmological or semi-analytic studies, for example, to model event rates for LISA or pulsar timing.

astro-ph.GA↗

arXiv2025

A Sea of Black Holes: Characterizing the LISA Signature for Stellar-Origin Black Hole Binaries

Observations by the LIGO, Virgo and KAGRA (LVK) detectors have provided new insights in the demographics of stellar-origin black hole binaries (sBHB). A few years before gravitational-wave signals from sBHB mergers are recorded in the LVK detectors, their early coalescence will leave a unique signature in the ESA/NASA mission Laser Interferometer Space Antenna (LISA). Multiband observations of sBHB sources between LISA and LVK detectors opens an unprecedented opportunity to investigate the astrophysical environment and multi-messenger early-alerts. In this study, we report the sBHB sources that will be present in the LISA data derived directly from the hydrodynamic cosmological simulation Illustris. By surveying snapshots across cosmological volume, metallicity and look-back time, we find that about tens to thousand sBHB candidates will be present in the LISA data for various combinations of mission lifetime. For estimates consistent with the LVK rates, we find that only 20 sBHBs across Illustris snapshots will be detected with significant confidence for a 10-year LISA mission, while a 4-year LISA mission would detect only 2 sBHBs. Our work paves the way for creating LISA mock data and bench marking LISA detection pipelines directly using cosmological simulations.

astro-ph.HE↗

arXiv2025

Comparing the Spatial Correlation of Binary Black Hole Mergers to Large-Scale Structure through the Illustris Simulation

Gravitational waves (GWs) have provided a new lens through which to view the universe beyond traditional electromagnetic methods. The upcoming space-based gravitational wave mission, Laser Interferometer Space Antenna (LISA), will give us the first glimpse of the sky in mHz gravitational waves, a waveband that contains a rich variety of sources including massive binary black hole (MBBH) mergers. In this work, we investigate the spatial distribution of MBBH mergers versus the galaxy distribution to determine how well LISA could be used as a unique and independent probe of large-scale structure. We compare the two-point correlation function (2pt CF) of MBBH mergers to that of galaxies within the cosmological hydrodynamic simulation IllustrisTNG. Our results show that MBBH mergers exhibit stronger clustering than galaxies at scales less than 10 Mpc $h^{-1}$, particularly at higher redshifts, and that the bias is relatively constant as a function of separation. These findings imply that the spatial distribution of MBBH mergers detectable by LISA could inform the observed galaxy distribution. In addition, this implies that searches for a cosmological background in LISA data could use a prior derived from large-scale structure observations to subtract the MBBH foreground.

astro-ph.CO↗

arXiv2025

Where Have All the Little Red Dots Gone? Supermassive Black Hole Binary Dynamics and its Impact on Galaxy Properties

Recent James Webb Space Telescope observations have revealed a peculiar class of galaxies at redshifts $z \gtrsim 6$, characterized by extremely high central stellar densities and overmassive central supermassive black holes (SMBHs), "little red dots" (LRDs). A critical question remains: If LRDs were common at high redshifts, how would they evolve into local elliptical galaxies with significantly lower central densities? To address this, we performed direct $N$-body simulations of LRD mergers, focusing on the coevolution of host galaxies and central SMBHs. We track the complete evolution of SMBH binaries into the three-body hardening and gravitational-wave (GW) emission phase. Our results demonstrate that during galaxy mergers, the central SMBHs can eject a substantial amount of mass from the galactic core via the three-body slingshot effect, leading to a decrease in central stellar surface density by an order of magnitude. Additionally, GW recoil can further contribute in making the galaxy centers less dense and more in alignment with low-redshift quiescent galaxies. This transformation occurs on a relatively short timescale of a few $\sim$100 Myr, implying that LRDs can evolve into lower-redshift elliptical galaxies by $z<4$. The timescales for our SMBH mergers vary between 100 Myr and 800 Myr, depending on the initial orbital parameters of the merging galaxies and the mass ratio of the SMBHs. Our findings provide a plausible mechanism for the transformation of LRDs into elliptical galaxies while highlighting the efficiency of SMBH mergers in such high-density environments, which plays a crucial role in SMBH growth.

astro-ph.GA↗

arXiv2025

ALEXIS: Recreating the X-Ray Emission from the Full Solar Disk as a Linear Combination of Discrete Regions in the Extreme Ultraviolet and Soft X-Rays

Despite a wealth of multi-wavelength, spatially resolved, time-domain solar activity data, an accurate and complete temporo-spatial solar flare census is unavailable, which impedes our understanding of the physics of flare production. We present an Automatically Labeled EUV and X-ray Incident SolarFlares (ALEXIS) pipeline, designed to decompose the X-Ray flux of the full solar disk into a minimum set of discrete regions on the Solar surface. ALEXIS returns an average RMSE between the XRS time series and the discrete EUV signals of 0.066 $\pm$ 0.036 for a randomly selected test bed sample of 1000 hour-long data segments from May 2010 - March 2020. Flare emission that requires multiple regions was found to be synchronous: flares occurring at the same time, sympathetic: flares separated by minutes, or needed to capture the background emission before and/or after the main flare. ALEXIS uses the original full resolution and cadence of both the Atmospheric Imaging Assembly Instrument and the GOES13-15 Solar X-Ray Imager. Comparison of the ALEXIS catalog with those produced by SWPC and SolarSoft show that these canonical databases need revisiting for 62$\%$ and 15$\%$ of the sub-sample, respectively. Additionally, we increased the number of flares reported by SWPC and SolarSoft by 15$\%$. Our pipeline misses 6.7$\%$ of the 1057 flare sub-sample and returns 5$\%$ of false positives from 1211 flares reported by ALEXIS. The ALEXIS catalog returns flare peak times, coordinates, the corrected scaled XRay magnitude, and the associated NOAA active region with a HARP identifier number independently from any external data products.

astro-ph.SR↗

arXiv2025

Multidisciplinary Science in the Multimessenger Era

Astrophysical observations of the cosmos allow us to probe extreme physics and answer foundational questions on our universe. Modern astronomy is increasingly operating under a holistic approach, probing the same question with multiple diagnostics including how sources vary over time, how they appear across the electromagnetic spectrum, and through their other signatures, including gravitational waves, neutrinos, cosmic rays, and dust on Earth. Astrophysical observations are now reaching the point where approximate physics models are insufficient. Key sources of interest are explosive transients, whose understanding requires multidisciplinary studies at the intersection of astrophysics, gravity, nuclear science, plasma physics, fluid dynamics and turbulence, computation, particle physics, atomic, molecular, and optical science, condensed matter and materials science, radiation transport, and high energy density physics. This white paper provides an overview of the major scientific advances that lay at the intersection of physics and astronomy and are best probed through time-domain and multimessenger astrophysics, an exploration of how multidisciplinary science can be fostered, and introductory descriptions of the relevant scientific disciplines and key astrophysical sources of interest.

astro-ph.HE↗

arXiv2025

Properties of 'Lite' Intermediate-Mass Black Hole Candidates in LIGO-Virgo's Third Observing Run

Over a hundred gravitational-wave (GW) detections and candidates have been reported from the first three observing runs of the Advanced LIGO-Virgo-KAGRA (LVK) detectors. Among these, the most intriguing events are binary black hole mergers that result in a 'lite' intermediate-mass black hole (IMBH) of ${\sim}10^2~\mathrm{M}_\odot$, such as GW170502 and GW190521. In this study, we investigate 11 GW candidates from LVK's Third Observing Run (April 2019-March 2020) that have a total detector-frame masses in the lite IMBH range. Using the Bayesian inference algorithm \texttt{RIFT}, we systematically analyze these candidates with three state-of-the-art waveform models that incorporate higher harmonics, which are crucial for resolving lite IMBHs in LVK data. For each candidate, we infer the pre-merger and post-merger black hole masses in the source frame, along with black hole spin projections across all three models. Under the assumption that these are binary black hole mergers, our analysis finds that 5 of them have a post-merger lite IMBH with masses ranging from $110\sim 350~\mathrm{M}_\odot$ with over 90\% confidence interval. Additionally, we note that one of their pre-merger black holes is within the pair-instability supernova mass gap ($60-120~\mathrm{M}_\odot$) with more than 90\% confidence interval, and additional two pre-merger black holes above the mass-gap. Furthermore, we report discrepancies among the three waveform models in their mass and spin inferences of lite IMBHs, with at least three GW candidates showing deviations beyond accepted statistical limits. While the astrophysical certainty of these candidates cannot be established, our study provides a foundation to probe the lite IMBH population that emerge within the low-frequency noise spectrum of LVK detectors.

astro-ph.HE↗

arXiv2024

The potential for long-lived intermediate mass black hole binaries in the lowest density dwarf galaxies

Intermediate Mass Black Hole (IMBH) mergers with masses $10^4 - 10^6$ $M_{\odot}$ are expected to produce gravitational waves (GWs) detectable by the Laser Interferometer Space Antenna (LISA) with high signal to noise ratios out to redshift 20. IMBH mergers are expected to take place within dwarf galaxies, however, the dynamics, timescales, and effect on their hosts are largely unexplored. In a previous study, we examined how IMBHs would pair and merge within nucleated dwarf galaxies. IMBHs in nucleated hosts evolve very efficiently, forming a binary system and coalescing within a few hundred million years. Although the fraction of dwarf galaxies ($10^7$ M$_{\odot} \leq$ $M_{\star} \leq 10^{10}$ M$_{\odot}$) hosting nuclear star clusters is between 60-100\%, this fraction drops to 20-70\% for lower-mass dwarfs ($M_{\star}\approx 10^7$ M$_{\odot}$), with the largest drop in low-density environments. Here, we extend our previous study by performing direct $N-$body simulations to explore the dynamics and evolution of IMBHs within non-nucleated dwarf galaxies, under the assumption that IMBHs exist within these dwarfs. To our surprise, none of IMBHs in our simulation suite merge within a Hubble time, despite many attaining high eccentricities $e \sim 0.7-0.95$. We conclude that extremely low stellar density environments in the centers of non-nucleated dwarfs do not provide an ample supply of stars to interact with IMBHs binary resulting in its stalling, in spite of triaxiality and high eccentricity, common means to drive a binary to coalescence. Our findings underline the importance of considering all detailed host properties to predict IMBH merger rates for LISA.

astro-ph.GA↗

arXiv2024

A Tale of Two Black Holes: Multiband Gravitational-Wave Measurement of Recoil Kicks

The non-linear dynamics of General Relativity leave their imprint on remnants of black hole mergers in the form of a recoil ``kick''. The kick has profound astrophysical implications across the black hole mass range from stellar to super-massive. However, a robust measurement of the kick for generic binaries from gravitational-wave observations has proved so far to be extremely challenging. In this \emph{letter}, we demonstrate the prospects of measuring black hole kicks through a multiband gravitational-wave network consisting of space mission LISA, the current earth-based detector network and a third-generation detector. For two distinct cases of remnant black hole kick (68 km/s, 1006 km/s) emerging from near identical pre-merger configuration of GW190521 -- the first confirmed intermediate-mass black hole -- we find that the multiband network will recover with 90\% credible level the projection of the kick vector relative to the orbital plane within tens of km/s accuracy. Such precise measurement of the kick offer a new set of multi-messenger follow-ups and unprecedented tests of astrophysical formation channels.

gr-qc↗

arXiv2024

A Parametric Study of the SASI Comparing General Relativistic and Nonrelativistic Treatments

We present numerical results from a parameter study of the standing accretion shock instability (SASI), investigating the impact of general relativity (GR) on the dynamics. Using GR hydrodynamics with GR gravity, and nonrelativistic (NR) hydrodynamics with Newtonian gravity, in an idealized model setting, we vary the initial radius of the shock and, by varying its mass and radius in concert, the proto-neutron star (PNS) compactness. We investigate four compactnesses expected in a post-bounce core-collapse supernova (CCSN). We find that GR leads to a longer SASI oscillation period, with ratios between the GR and NR cases as large as 1.29 for the highest-compactness suite. We also find that GR leads to a slower SASI growth rate, with ratios between the GR and NR cases as low as 0.47 for the highest-compactness suite. We discuss implications of our results for CCSN simulations.

astro-ph.HE↗