Eclipses of Nearby Radio-Loud Galactic Nuclei by Stars in Nuclear Star Clusters

TL;DR

This paper explores the potential for detecting eclipses of radio-loud galactic nuclei by stars in nuclear clusters at millimeter wavelengths, offering a new method to study SMBHs and their surrounding stellar environments.

Contribution

It introduces the concept of observing stellar eclipses of radio cores in nearby active galactic nuclei at millimeter wavelengths as a novel probe of SMBHs and nuclear star cluster composition.

Findings

Evolved stars with radii > 500 R_sun can cause ~10% eclipses in the millimeter domain.

Eclipse recurrence timescales are at least 10 years with durations around 10 days.

Eclipse profiles vary with frequency, becoming shallower and broader at lower frequencies.

Abstract

It is of a general interest to look for signatures of stellar bodies orbiting supermassive black holes (SMBHs) in galactic nuclei other than the Galactic center. Previously stellar transits were analyzed in UV, optical, and X-ray domains as well as potential microlensing signatures due to more compact bodies orbiting SMBH accretion disks. Here we complement previous studies by considering nearby ($z=0.001$) radio-loud active galactic nuclei targeted by different facilities in the millimeter domain. At these wavelengths the radio core is sufficiently small so that it can be occulted by large evolved stars in dense nuclear star clusters. We find that in the millimeter domain evolved stars with stellar radii of $\gtrsim 500\,R_{\odot}$ can cause eclipses with the relative depth of $\sim 10\%$. Typical recurrence timescales are at least 10 years and the eclipse durations are $\sim 10$ days. Towards lower frequencies the eclipse temporal profiles become shallower and broader while towards higher frequencies they are deeper and narrower. Although expected to be rare due to selection effects and evolved stars being prone to tidal disruption, recurrent eclipses of mm radio cores can be applied to infer SMBH masses and constrain the composition of the Nuclear Star Cluster of the host nucleus.