arXiv subjects

Mark Dodici

Publications and source records attributed to Mark Dodici.

5 recordsLinked to original sources

arXiv2026

Binary disruptions driven by massive disks around massive black holes

Accretion disks around massive black holes (MBHs) in galactic nuclei can contain significant mass, in which case their non-spherical potentials exert significant torques on single and binary stars orbiting the MBHs. These torques can drive orbits to very large eccentricities. Previous works have shown that this driving can cause disruptions of single stars by the tidal gravity of the MBH. Here, we characterize the ability of these torques to drive binary stars to the point of disruption via the Hills mechanism. We derive semi-analytical estimates, validated with numerical simulations, of the number of binary disruptions driven by a generic disk in a generic nucleus. Using these results, we estimate that the formation of the ~5-Myr-old disk of stars in the Galactic Center drove a burst of ~10^2 binary disruptions. These disruptions produced an excess of S-cluster stars and hypervelocity stars --- possibly including S5-HVS1, the fastest-known hypervelocity star. In other galaxies, analogues of S-cluster stars produced by this process may evolve into tidal disruption events following a disk phase. Hypervelocity star observations may help clarify the importance of disk-driven disruptions, which eject stars nearly isotropically and in temporal bursts --- a unique combination among processes driving binary disruptions.

astro-ph.GA↗

arXiv2025

Dynamical evolution of stellar binaries in galactic centers

Stellar binaries in galactic centers are relevant to several observable phenomena, including hypervelocity stars, X-ray binaries, and mergers of stars and compact objects; however, we know little about the properties of these binaries. Past works have suggested that a small fraction of them should contract to a few stellar radii or collide, due to the co-operation of stellar tides and the eccentricity oscillations induced by the strong tidal field of the central massive black hole. We revisit this model with several updates. We first argue that when a binary's pericenter separation is driven down to a few stellar radii, diffusive excitation of stellar tides should quickly contract the orbit, saving the stars from collision. Instead, the stars should end up as a very tight binary. We then show that vector resonant relaxation and perturbations from passing stars -- effects not included in past models -- dramatically increase the prevalence of such encounters. In numerical experiments, we find that 1 in 5 binaries around 1 pc from Sgr A* should tidally contract in this way while still on the main sequence. This rate climbs to 3 in 5 around 0.01 pc, inward of which it plateaus. We briefly discuss observable implications of these results, with particular attention to young stellar binaries in the Galactic Center.

astro-ph.GA↗

arXiv2024

Studying Binary Formation under Dynamical Friction Using Hill's Problem

Using the equations of motion from Hill's problem, with added accelerations for different forms of dynamical friction, we provide the (to-date) broadest scale-free study of friction-driven binary formation in gaseous disks and stellar clusters. We focus mainly on binary formation between stellar-mass black holes in active galactic nuclei (AGNi), considering both gas dynamical friction from AGN disks and stellar dynamical friction from the nuclear star cluster. We first find simple, dimensionless friction coefficients that approximate the effects of standard models for gas and stellar dynamical friction. We perform extensive simulations of Hill's problem under such friction, and we present a picture of binary formation through encounters between single stars on nearby orbits, as a function of friction parameter, eccentricity, and inclination. Notably, we find that the local binary formation rate is a linear function of the friction coefficient so long as the friction is weak. Due to the dimensionless nature of our model problem, our findings are generalizable to binary formation at all scales (e.g., intermediate-mass black holes in a star cluster, planetesimals in a gaseous disk).

astro-ph.GA↗

arXiv2023

Improving Undergraduate Astronomy Students' Skills with Research Literature via Accessible Summaries: An Exploratory Case Study with Astrobites-based Reading Assignments

Undergraduate physics and astronomy students are expected to engage with scientific literature as they begin their research careers, but reading comprehension skills are rarely explicitly taught in major courses. We seek to determine the efficacy of a reading assignment designed to improve undergraduate astronomy (or related) majors' perceived ability to engage with research literature by using accessible summaries of current research written by experts in the field. During the 2022-2023 academic year, faculty members from six institutions incorporated reading assignments using accessible summaries from Astrobites into their undergraduate astronomy major courses, surveyed their students before and after the activities, and participated in follow-up interviews with our research team. Quantitative and qualitative survey data from 52 students show that students' perceptions of their abilities with jargon and identifying main takeaways of a paper significantly improved with use of the tested assignment template. Additionally, students report increased confidence of their abilities within astronomy after exposure to these assignments, and instructors valued a ready-to-use resource to incorporate reading comprehension in their pedagogy. This exploratory case study with Astrobites-based assignments suggests that incorporating current research in the undergraduate classroom through accessible literature summaries may increase students' confidence and ability to engage with research literature, assisting in their preparation for participation in research careers.

physics.ed-ph↗

arXiv2021

Polycyclic Aromatic Hydrocarbons, the Anomalous Microwave Emission, and Their Connection to the Cold Neutral Medium

Using new large area maps of the cold neutral medium (CNM) fraction, $f_{\rm CNM}$, we investigate the relationship between the CNM, the abundance of polycyclic aromatic hydrocarbons (PAHs), and the anomalous microwave emission (AME). We first present our $f_{\rm CNM}$ map based on full-sky HI4PI data, using a convolutional neural network to covert the spectroscopic HI data to $f_{\rm CNM}$. We demonstrate that $f_{\rm CNM}$ is strongly correlated with the fraction of dust in PAHs as estimated from mid- and far-infrared dust emission. In contrast, we find no correlation between $f_{\rm CNM}$ and the amount of AME per dust emission, nor between $f_{\rm CNM}$ and the AME peak frequency. These results suggest PAHs preferentially reside in cold, relatively dense gas, perhaps owing to enhanced destruction in more diffuse media. The lack of correlation between $f_{\rm CNM}$ and AME peak frequency is in tension with expectations from theoretical models positing different spectral energy distributions of AME in the cold versus warm neutral medium. We suggest that different PAH abundances and emission physics in different interstellar environments may explain the weaker than expected correlation between 12$\mu$m PAH emission and AME even if PAHs are the AME carriers.

astro-ph.GA↗