Tidal Disruptions of Main-sequence Stars of Varying Mass and Age: Inferences from the Composition of the Fallback Material
Physical and Biological Sciences
Lamat
We study black holes within galactic nuclei by analyzing the movement of stars swarming around them. When the conditions are right we can observe the black hole’s destructive power. With the right trajectory and the strong gravitational force of the black hole the stars are put on a course to be squeezed and spun enough to break it apart. The material gravitationally bound to the black hole after the disruption accretes onto the black hole and creates a powerful flare. We use a simple framework to calculate the time evolution of the composition of the accreted fallback material onto a supermassive black hole arising from the tidal disruption of main sequence stars. We study stars with masses between 0.8 and 3.0 solar mass, at various evolutionary stages, built using the Modules for Experiments in Stellar Astrophysics code. We show that most stars develop enhancements in nitrogen (14N) and depletions in carbon (12C) and oxygen (16O) over their lifetimes, and that these features are more pronounced for higher mass stars. We and that, in an accretion-powered tidal disruption flare, these features become prominent only after the time of peak of the fallback rate and appear at earlier times for stars of increasing mass. We postulate that no severe compositional changes resulting from the fallback material should be expected near peak for a wide range of stellar masses and, as such, are unable to explain the extreme helium-to-hydrogen line ratios observed in some TDEs. On the other hand, the resulting compositional changes could help explain the presence of nitrogen-rich features, which are currently only detected after peak. When combined with the shape of the light curve, the time evolution of the composition of the fallback material provides a clear method to help constrain the nature of the disrupted star. This will enable a better characterization of the event by helping break the degeneracy between the mass of the star and the mass of the black hole when ting tidal disruption light curves.
