Eugene, Oregon — Astronomers have uncovered a remarkable phenomenon in the cosmos, as they continue to study a supermassive black hole that has exhibited unexpected behavior since it was first observed four years ago. Initially discovered consuming a star, this event, known as a tidal disruption event (TDE), is revealing significant insights into the dynamics of black holes and their surrounding environments.
The TDE, designated as AT2018hyz, was first identified by a team monitoring astronomical transients in 2018. After a period of radio silence, researchers detected radio emissions from the event in 2022. Recent studies published in The Astrophysical Journal indicate that energy output from AT2018hyz is still on the rise, over three years after its initial detection in optical light. This sustained increase is noteworthy, suggesting ongoing processes at play in the vicinity of the supermassive black hole.
Lead researcher Yvette Cendes, an Assistant Professor of Physics at the University of Oregon, emphasized the significance of these ongoing observations. “We present ongoing radio observations of AT2018hyz, which show a significant increase in energy across multiple frequencies,” she said. This sustained brightening is unusual for TDEs, which typically see a decline in energy output over time.
Astrophysical models propose two potential explanations for the rising emissions. One theory suggests a delayed spherical outflow, where energy is expelled approximately 620 days post-disruption, indicating a complex evolution of the outflow. Alternatively, a highly off-axis jet could be responsible, traveling at relativistic speeds. According to the researchers, this jet may initially suppress radio emissions due to beaming effects, only to become increasingly visible as it decelerates.
The new findings suggest that the radio emissions from AT2018hyz could continue to escalate, with a projected peak around 2027, a timeline that astonished Cendes. “This is really unusual; I can’t think of any other event that has shown such a prolonged rise in emissions,” she added.
The energy output of AT2018hyz ranks it among the most powerful events observed, akin to gamma-ray bursts — some of the universe’s brightest explosions. Intriguingly, the research yielded a striking comparison: AT2018hyz emits at least a trillion times more energy than the fictional Death Star from the Star Wars franchise, demonstrating just how extraordinary this cosmic event is.
Despite the excitement surrounding these findings, unanswered questions remain. Cendes expressed concerns about whether similar rising emissions might be occurring with other black holes and TDEs across the universe. “If an explosion occurs, it’s unlikely we should see something years later without prior observations,” she stated, pointing to the competitive nature of acquiring telescope time for such inquiries.
The TDE AT2018hyz is not isolated in its delayed radio emissions, but its intense luminosity sets it apart within its category. Cendes and her team are committed to further investigating this phenomenon, employing advanced observational strategies to monitor the ongoing evolution of the black hole and its surrounding medium.
This research paves the way for understanding black hole behavior and challenges existing theories regarding stellar disruptions. By continuing to study AT2018hyz, scientists hope to shed light on the ongoing mysteries of the universe, revealing deeper insights into the forces that shape cosmic phenomena.