An international team of astronomers has investigated a short-lived optical flare designated AT2022zod. As a result, they found evidence indicating that this flare is an unusual tidal disruption event. The findings were presented in a research paper published Dec. 1 on the arXiv pre-print server.
When a star passes close enough to a supermassive black hole and is pulled apart by the black hole’s tidal forces, it triggers the process of disruption, which is known as a tidal disruption event (TDE). Afterward, the tidally disrupted stellar debris starts raining down on the black hole, and radiation emerges from the innermost region of accreting debris, which is an indicator of the presence of a TDE.
A mysterious flare
AT2022zod was identified as an optical flare, which lasted slightly more than a month—from October 13 to November 18, 2022, with a rise time of approximately 13.24 days. The flare had an apparent magnitude of 19.2 mag and was identified in the elliptical galaxy SDSS J105602.80+561214.7 at a redshift of 0.11, within 10,000 light years from the galaxy’s center.
A group of astronomers led by Kristen C. Dage of Curtin University in Perth, Australia, decided to investigate AT2022zod to shed more light on its origin.
“We examined and systematically constrained several possible origins for the flaring event AT2022zod, including AGN [active galactic nucleus] variability, a supernova explosion, a compact-object merger, and the tidal disruption of a star by a SMBH [supermassive black hole]. We first characterized the photometric and temporal properties of AT2022zod,” the researchers explain.
Uncovering the nature of luminous transient
The study found that AT2022zod is an unusually luminous transient as it reached a much higher peak luminosity than most events with similar duration. This makes it unlikely to have originated from the central SMBH of the host galaxy SDSS J105602.80+561214.7.
Furthermore, based on the collected data, the astronomers strongly disfavored AGN variability, supernovae, kilonovae, and periodic TDE as possible scenarios that could explain the origin of AT2022zod.
The authors of the paper suggest that AT2022zod may be a tidal disruption event by a massive black hole (MBH) in the intermediate-mass range or by a star disrupted by the central SMBH on a non-parabolic orbit. They insist that the most plausible origin for AT2022zod is a TDE of a star by a MBH embedded in an ultra-compact dwarf galaxy (UCD).
“We argue that the most likely origin is a UCD embedded in the host galaxy, hosting its own massive black hole,” the scientists write.
They note that the environment of AT2022zod closely resembles those inferred for several other TDEs associated with MBHs.
Summing up the results, the authors of the study emphasize the importance of finding more unusual TDEs like AT2022zod. This can be achieved by Vera C. Rubin Observatory for and can help us improve the MBH census up to higher redshifts.
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More information:
Kristen C. Dage et al, AT2022zod: An Unusual Tidal Disruption Event in an Elliptical Galaxy at Redshift 0.11, arXiv (2025). DOI: 10.48550/arxiv.2512.02136
Journal information:
arXiv
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