Rare Optical Flare AT2022zod May Be an Unusual Tidal Disruption Event, Astronomers Say
International Team Investigates a Powerful and Mysterious Flare
Study Posted on arXiv Reveals New Clues to a Rare Phenomenon
An international team of astronomers has examined a brief but intense optical flare known as AT2022zod, uncovering evidence that it may represent an unusual tidal disruption event. Their results, posted on 1 December on the arXiv pre-print server, shed new light on this rare phenomenon.
A tidal disruption event (TDE) occurs when a star wanders too close to a supermassive black hole and is torn apart by immense tidal forces. The shredded stellar material then spirals inward, producing radiation from the innermost regions of the accreting debris—a telltale hallmark of a TDE.
A Mysterious Flare Observed in 2022
Optical Outburst Lasted Just Over a Month
AT2022zod was observed as an optical flare lasting just over a month, from 13 October to 18 November 2022, with a rise of roughly 13.24 days. Reaching an apparent magnitude of 19.2, the flare emerged from the elliptical galaxy SDSS J105602.80+561214.7 at a redshift of 0.11, situated around 10,000 light years from the galactic center.
The phenomenon drew the attention of a team led by Kristen C. Dage of Curtin University in Perth, who sought to clarify its origins.
"We examined and systematically assessed several potential explanations for the outburst AT2022zod, including AGN variability, a supernova, a compact-object merger, and the tidal disruption of a star by a supermassive black hole. Our first step was to characterize its photometric and temporal behaviour," the authors noted.
Uncovering the Nature of the Luminous Transient
Analysis Suggests an Exceptionally Bright and Unusual Event
The analysis revealed that AT2022zod is an unusually bright transient, achieving a peak luminosity far exceeding that of most events of comparable duration. This makes it improbable that the flare originated from the central supermassive black hole of its host galaxy, SDSS J105602.80+561214.7.
In addition, the data strongly rule out AGN variability, supernovae, kilonovae and periodic tidal disruption events as viable explanations.
Possible Explanation Points to Massive Black Hole in Ultra-Compact Dwarf Galaxy
Researchers Consider Two TDE Scenarios
The Researchers propose that AT2022zod may instead represent a tidal disruption event caused either by an intermediate-mass black hole or by a star torn apart by the galaxy's central SMBH on a non-parabolic orbit. they conclude that the most likely scenario is a TDE involving a massive black hole embedded within an ultra-compact dwarf galaxy.
"The evidence points most convincingly to an ultra-compact dwarf galaxy within the host, harbouring its own massive black hole," the authors note.
They observe that AT2022zod's environment is strikingly similar to that associated with other TDEs believed to involve massive black hole.
Future Observations Expected to Reveal More Rare Events
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The study's authors emphasize that uncovering more rare events like AT2022zod—an aim well supported by the forthcoming Vera C. Rubin Observatory—will be essential for improving the inventory of massive black holes across higher redshift ranges.
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