Monash University astronomers have contributed to a groundbreaking breakthrough in understanding the dramatic fate of stars that get too close to the supermassive black hole at the center of our galaxy. Through innovative simulations, an international team of researchers led by Professor Daniel Price from the School of Physics and Astronomy and former student David Liptai has captured the complex process of how these stars are ripped apart and swallowed by the black hole, providing new insights into the mysterious optical phenomenon of ultraviolet radiation observed during these catastrophic events. “This is the first coherent simulation of the destruction of a star by a supermassive black hole via tidal forces, followed by the evolution of the resulting debris over a period of a year,” Professor Price said. “Our simulation provides a new perspective on the final moments of a star close to a supermassive black hole,” he said. “Capturing the complete evolution of the debris allows us to link our simulations with the increasing number of stellar disruption events confirmed by telescopic surveys.” The research, published in The Astrophysical Journal Letters, is a major advance in astrophysics and opens up new avenues for studying the behavior of matter in extreme gravitational fields and the life cycles of stars and black holes. When a star gets too close to a supermassive black hole, its powerful gravity tears it apart in a process called tidal disruption event (TDE). The stellar debris forms a stream that eventually feeds into the black hole. The stellar debris forms a disk that swirls around the black hole and emits powerful radiation across the entire electromagnetic spectrum. However, many aspects of the TDE are still poorly understood. New simulations show that this debris forms an asymmetric bubble around the black hole that reprocesses energy and produces the light curve observed with lower temperatures, lower luminosity and gas speeds of 10,000-20,000 km/s. “This work helps explain some puzzling properties of the observed TDEs,” Professor Price said. “If we use the analogy of the human body, our body temperature doesn’t change much when we eat lunch because we convert the energy from our lunch into infrared wavelengths. “Similarly, TDEs have black holes whose stomachs are normally invisible because they are suffocated by material that re-radiates at optical wavelengths. Our simulations show how this suffocation occurs.” Other mysteries explained by the new simulations include: Why tidal disruption is observed at optical wavelengths, rather than the X-ray wavelengths where X-rays are expected from accretion onto a supermassive black hole. Why the observed temperatures are more consistent with a stellar photosphere than the expected hot accretion disk. Why are the observed stellar disruption events weaker than expected from models in which black holes efficiently eat matter? Why does the spectrum of observed events indicate that matter is moving towards us at a few percent of the speed of light (10-20,000 km/s)? The research team used the advanced code phantom to smooth particle hydrodynamics and integrate general relativistic effects to accurately simulate the dynamics of the star and debris. This level of detail is crucial for capturing the complex interactions and energy dissipation processes that occur during and after the destruction of the star. “The results support the theoretical existence of an Eddington shell that acts as a processing layer for the emitted energy, explaining the optical and ultraviolet emissions observed during TDEs,” Professor Price said. “The model also provides a possible explanation for the differences in the X-ray and optical light curves observed in these events, suggesting that different viewing angles could potentially explain these discrepancies.”
source:Astrophysical Journal Letters