In an exciting breakthrough in the study of tidal disruption events (TDEs), astronomers have captured the intense and rapid brightening of AT2018hyz, a TDE located 665 million light-years away. This discovery, published in a new study on the arXiv preprint server, marks a pivotal moment in our understanding of the energetic phenomena triggered when a star is torn apart by the gravitational forces of a supermassive black hole. By employing an international array of telescopes, including MeerKAT and ALMA, the researchers have been able to track the radio emission from AT2018hyz, revealing a startling pattern of luminosity growth that challenges previous models of TDE behavior.
What is a Tidal Disruption Event?
A Tidal Disruption Event occurs when a star ventures too close to a supermassive black hole and is ripped apart by the black hole’s tidal forces. The stellar debris, which rains down on the black hole, forms an accretion disk and generates high-energy radiation. This radiation is one of the key signatures of a TDE and has been studied extensively in various cosmic events. The observation of AT2018hyz marks another important step in understanding the diverse outcomes of these violent cosmic interactions. Located in a post-starburst galaxy known as 2MASS J10065085+0141342, AT2018hyz was initially discovered in 2018 by the All Sky Automated Survey for SuperNovae (ASASS-SN).
While TDEs are relatively common, the radio emission observed from AT2018hyz was unlike anything seen in previous TDEs. This unique feature has triggered a reevaluation of the physical processes at play in such events, offering new insights into the behavior of matter under extreme conditions.
Rapid Brightening in the Radio Spectrum
The recent observational campaign spanning two years has revealed an unprecedented rapid rise in the radio luminosity of AT2018hyz. The data show that the radio emission from this TDE increased at a staggering rate across all frequencies, surpassing the luminosity of previous non-relativistic TDEs. According to the research, this rapid brightening reached a peak luminosity of approximately 10 duodecillion erg/s, a figure that rivals that of the well-known relativistic TDE, Sw 1644+57.
This breakthrough is significant because it demonstrates that AT2018hyz is among the most luminous non-relativistic TDEs observed to date. The study’s authors point out that this behavior challenges previous assumptions about the nature of radio emissions from TDEs. As they explain, “The observed behavior is consistent with two possible scenarios: (i) a delayed spherical outflow launched about 620 days post-disruption with a velocity of ≈ 0.3c and an energy of ∼ 1050 erg, and (ii) a highly off-axis (≈ 80 − 90◦) relativistic jet with a Lorentz factor of Γ ∼ 8 and EK ≈ 1052 erg.”
Luminosity light curve over time of AT2018hyz in several frequency bands, including early upper limits (triangles) and the late-time detections starting at about 970 days (circles). Credit: arXiv (2025). DOI: 10.48550/arxiv.2507.08998
Understanding the Origin of the Radio Emission
The nature of the radio emission from AT2018hyz is still a subject of intense debate. The two hypotheses put forward by the research team suggest distinct mechanisms behind the observed brightening. The first theory involves a spherical outflow, which would have been launched about 620 days after the star’s disruption. This outflow would have a velocity of approximately 0.3c (about 30% the speed of light) and an energy of approximately 1050 erg. This scenario posits that the rapid increase in radio luminosity is due to the dispersal of energy across a broad area, possibly caused by the delayed ejection of material from the disrupted star.
On the other hand, the second hypothesis suggests the presence of a relativistic jet that is highly off-axis, meaning that it is directed at a significant angle to our line of sight. This jet would have a Lorentz factor of Γ ∼ 8, indicating that it is traveling at relativistic speeds, and an energy of EK ≈ 1052 erg. A relativistic jet traveling at these speeds would produce intense radiation that could account for the observed rapid brightening of AT2018hyz in the radio spectrum.