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arXiv · 2605.15145

Eclipses of Nearby Millimeter-Bright Galactic Nuclei by Stars in Nuclear Star Clusters

Michal Zajaček
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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 ($z=0.001$) millimeter-bright active galactic nuclei targeted by different facilities in the millimeter domain. At these wavelengths the jet base and the nuclear ring are sufficiently compact so that they 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 $\sim 10-40\%$. 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, eclipses of millimeter radio cores can be applied to estimate the distance of the extragalactic star from the SMBH and its stellar radius. In case the eclipse is recurring, we provide a relation for estimating the SMBH mass.

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Michal Zajaček. 2026-05-14. Eclipses of Nearby Millimeter-Bright Galactic Nuclei by Stars in Nuclear Star Clusters. https://arxiv.org/abs/2605.15145

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