arXiv subjects

Alberto Salvarese

Publications and source records attributed to Alberto Salvarese.

4 recordsLinked to original sources

arXiv2026

Eccentricity as a Magnifying Glass: Precision Population Inference Enabled by Eccentric Neutron Star-Black Hole Mergers

The formation history of compact binary systems remains one of the key open questions in astrophysics. Theoretical studies generally favor isolated binary evolution for neutron star-black hole (NSBH) systems, which tends to produce nearly circular orbits. However, recent analyses of the gravitational-wave event GW200105 indicate that its source has measurable eccentricity, suggesting that alternative formation channels may also contribute. It has been shown that the intrinsic parameters of eccentric NSBH mergers, such as the component masses and spins, are much better measured than circular mergers with LIGO-Virgo-KAGRA (LVK) observatories. We explore how such eccentricity-enhanced parameter measurements can affect the inference of NSBH formation channels. We find that sharper measurements of the effective spin parameter $\chi_{\rm eff}$ increase the fraction of systems for which negative values can be confidently identified, allowing for the clear measurement of a spin-orbit misaligned event every $\sim 2.5$ eccentric NSBH detections for an isotropically distributed population in the fifth LVK observing run (O5). Improved NS mass measurements provide better constraining power for NS mass distributions, potentially revealing structure and tightening the bounds that can be drawn on their upper and lower masses. Similarly, the recovery of a metallicity-dependent BH mass distribution is improved by eccentricity-enhanced measurements. Finally, we show that the proposed population-level eccentricity distribution for dynamical-formation channels can be tested by the end of O5.

astro-ph.HE↗

arXiv2026

Identifying the host of compact binary mergers

Finding the host galaxies of stellar-mass compact binary mergers will open a new window for studying their formation histories and measuring key cosmological parameters, such as the Hubble constant. To date, only one merger, GW170817, has had its host galaxy confidently identified through electromagnetic counterpart observations. The large localization volumes from the LIGO-Virgo-KAGRA (LVK) network, combined with the lack of electromagnetic emission for most events, make host identification challenging. However, as the sensitivity of the gravitational-wave (GW) detector network improves, events are becoming increasingly well localized. Furthermore, galaxy luminosity traces mass or star formation rate, and thus correlates with the probability of hosting a merger. Focusing on the most luminous galaxies within the localization volumes of the best-localized GW events, we estimate the corresponding Hubble constant for each galaxy by combining its redshift with the luminosity distance inferred from LVK observations. For the well-localized LVK events \texttt{S250207bg}, \texttt{GW190814}, and \texttt{S250830bp}, we find only $1$, $1$, and $4$ galaxies, respectively, when restricting the analysis to the most luminous $1\%$ of galaxies above $L_{\rm th} \sim 10^{11} h^{-2} L_{\odot}$ in each event's localization volume and adopting a broad $H_0$ prior. The probability of these galaxies being random, and not associated with the GW events, is $29$-$36\%$ across the three events. We encourage further follow-up observations of these candidate host galaxies. We expect this approach to become increasingly powerful in future LVK observing runs, enabling constraints on merger formation histories and measurements of the Hubble constant.

astro-ph.CO↗

arXiv2025

Listening Across the Cosmic Time: Standard Sirens from Ground- and Space-Based Missions in the Next Decade

Precise measurement of the Hubble parameter will enable stringent tests of the standard model for cosmology. Standard sirens, using the luminosity distances measured by gravitational-wave observations of compact binary mergers, are expected to provide such measurements independently in the next decade. With the ground- and space-based gravitational wave observatories, the LIGO-Virgo-KAGRA (LVK) network and the Laser Interferometer Space Antenna (LISA), different types of standard sirens altogether will place constraints across a wide redshift range. In this paper, we forecast the precisions of standard siren Hubble parameter measurements and compare various scenarios, accounting for the dominant sources of systematic uncertainty. Specifically, we find a $2\%$ constraint on $H_0$, a $1.5-3\%$ constraint on $H(z)$ at $z=1$, and a $3-5\%$ constraint on $H(z)$ at $z=7$ when combining LVK and LISA standard sirens with precise redshift measurements from electromagnetic counterpart observations. We do not find a significant improvement when including standard sirens with no EM counterpart, but which rely on features in the black hole mass distribution, and the potential systematics introduced by the possible redshift evolution of such features could further degrade the measurement accuracy if not properly accounted for.

astro-ph.CO↗

arXiv2024

Mitigating the binary viewing angle bias for standard sirens

The inconsistency between experiments in the measurements of the local Universe expansion rate, the Hubble constant, suggests unknown systematics in the existing experiments or new physics. Gravitational-wave standard sirens, a method to independently provide direct measurements of the Hubble constant, have the potential to address this tension. Before that, it is critical to ensure there is no substantial systematics in the standard siren method. A significant systematic has been identified when the viewing angle of the gravitational-wave sources, the compact binary coalescences, is inferred inaccurately from electromagnetic observations of the sources. Such systematic has led to more than 10% discrepancy in the standard siren Hubble constant measurements with the observations of binary neutron star merger, GW170817. In this Letter, we develop a new formalism to infer and mitigate this systematic. We demonstrate that the systematic uncertainty of the Hubble constant measurements can be reduced to smaller than their statistical uncertainty with 5, 10, and 20 binary neutron star merger observations. We show that our formalism successfully reduces the systematics even if the shape of the biased viewing angle distribution does not follow precisely the model we choose. Our formalism ensures unbiased standard siren Hubble constant measurements when the binary viewing angles are inferred from electromagnetic observations.

astro-ph.CO↗