Scientific Paper

An international team of astronomers has discovered the first radio-bright tidal disruption event (TDE) occurring outside a galaxy's center, combining data from the Atacama Large Millimeter/submillimeter Array (ALMA) and from the Very Large Array (VLA) of the U.S. National Science Foundation National Radio Astronomy Observatory (NSF NRAO), along with several partner telescopes. The event, designated AT 2024tvd, revealed the fastest-evolving radio signals ever observed from this type of cosmic catastrophe.

The discovery, led by principal investigators Itai Sfaradi and Raffaella Margutti of the University of California, Berkeley, and others, represents a significant breakthrough in understanding how massive black holes can hide in unexpected places throughout the universe.

"This is truly extraordinary," said Sfaradi, lead author of the study. "Not only is this the first time we've observed such bright radio emission from a tidal disruption event happening away from a galaxy's center, but it's also evolving faster than anything we've seen before."

Tidal disruption events occur when a star ventures too close to a massive black hole and is torn apart by the black hole's immense gravitational forces. While these events typically occur at the centers of galaxies where supermassive black holes reside, AT 2024tvd was discovered approximately 0.8 kiloparsecs (about 2,600 light-years) away from its host galaxy's center.

The international team observed the event in great detail using a network of radio telescopes that covered a wide range of wavelengths, from centimeters to millimeters. Their data revealed an exceptionally fast and unusual evolution never before seen in this kind of phenomenon. The event produced two separate bursts of radio waves that brightened and faded far more rapidly than any known tidal disruption event. The first burst increased in brightness over a very short period of time and then dimmed almost as quickly, while the second flared up and faded even faster. These dramatic changes occurred on timescales many times shorter than those astronomers typically observe, showing that this was an extraordinarily dynamic and short-lived event.

"The radio emission from AT 2024tvd evolves so rapidly that it stands out even among the most extreme cosmic events we know," explained co-principal investigator Raffaella Margutti. "These observations are revealing new physics about how material behaves when launched from the vicinity of black holes," added Kate Alexander, PI of the VLA Program and professor at the University of Arizona. 

The discovery utilized an extensive network of radio telescopes, including NSF NRAO's VLA and ALMA, the Arcminute Micro-Kelvin Imager Large Array (AMI-LA), the Allen Telescope Array (ATA), and the Submillimeter Array (SMA). This multi-telescope approach allowed the team to track the event's evolution across a wide range of radio frequencies over approximately 300 days.

The research suggests that the rapid radio evolution results from at least one—and possibly two—outflows launched significantly after the initial stellar disruption. The team's analysis indicates these outflows were likely launched 80 and 170 days after the optical discovery, challenging traditional models of how tidal disruption events unfold.

"What makes this discovery even more remarkable is that it reveals a massive black hole that would otherwise be invisible to us," said Raffaella Margutti, "The only reason we can detect this wandering black hole is because it happened to tear apart a star and produce these incredibly bright radio signals."

The off-nuclear position of this TDE provides crucial insights into the population of massive black holes that may be wandering through galaxies or recoiling from past interactions. Current theories suggest such black holes could result from triple black hole interactions or be remnants from galaxy mergers.

The team's sophisticated analysis also marks the first time that both free-free absorption and inverse-Compton cooling have been considered together in modeling TDE radio emission, providing new tools for understanding these extreme events.

"This discovery opens up entirely new possibilities for finding hidden black holes throughout the universe," noted Itai Sfaradi. "With upcoming sky surveys, we may discover that these off-nuclear tidal disruption events are more common than we thought."

The research also revealed a potential connection between the launch of radio-emitting outflows and changes in the event's X-ray emission, suggesting a link to accretion processes around the black hole.

AT 2024tvd was initially discovered by the Zwicky Transient Facility on August 25, 2024, at optical wavelengths before follow-up observations revealed its radio brightness and off-nuclear nature.

Additional Information

The findings are published in The Astrophysical Journal Letters, and you can read them HERE.

This text is based on the press release by the National Radio Astronomy Observatory (NRAO), an ALMA partner on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.

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