Periodic Reporting for period 4 - Cat-In-hAT (Catastrophic Interactions of Binary Stars and the Associated Transients)
Periodo di rendicontazione: 2023-07-01 al 2025-06-30
The research in this project addressed open questions concerning the common envelope evolution (CEE), which is a cataclysmic phase in the evolution of binary stars and which enables evolutionary outcomes unachievable in other ways. A strong, recent driver to better understand CEE comes from the observations of merging black holes and neutron stars with gravitational waves. A new observational probe of CEE are transient brightenings called Luminous red novae. In this project, we performed computer simulations to comprehensively examine different phases of CEE with a particular emphasis on the accompanying transients.
CEE can begin in several ways. By identifying and studying each of these ways we aim to assess which binaries will go through CEE. Perhaps the most common way to start CEE is when the transfer of mass between two stars in an orbiting binary becomes unstable. An important ingredient needed to assess the mass transfer (in)stability in stellar evolution calculations is the relation between the size of the star (or rather by how much it overfills its so-called Roche lobe) and the mass transfer rate. Furthermore, loss of mass from one of the stars will alter its internal structure, which serves as a starting point for the subsequent more dynamical evolution. Another way to start CEE is when a star on an eccentric orbit grazes its companion. Each grazing ejects a little bit of mass and tightens the orbit.
The transient brightening associated with the dynamical phase of CEE can reveal new information about the progenitor binary system, the mechanism of its instability, and the surrounding medium. To successfully model these transients, we need incorporate a number of physical effects such as recombination and ionization of various elements, formation of dust and molecules, and transport of radiation inside this environment.
Finally, dynamical interactions inside CEE eventually get weaker and the system evolution slows down. Further evolution includes interplay between the binary orbit and the remaining, expanding gas. A number of different phenomena can play a role in this late phase, in particular magnetic fields and the possibility of collimated bipolar outflows. Our goal here was to perform dedicated multi-dimensional simulations of this phase and link them to preceding dynamical evolution and observed phenomena.
CEE can begin in several ways. By identifying and studying each of these ways we aim to assess which binaries will go through CEE. Perhaps the most common way to start CEE is when the transfer of mass between two stars in an orbiting binary becomes unstable. An important ingredient needed to assess the mass transfer (in)stability in stellar evolution calculations is the relation between the size of the star (or rather by how much it overfills its so-called Roche lobe) and the mass transfer rate. Furthermore, loss of mass from one of the stars will alter its internal structure, which serves as a starting point for the subsequent more dynamical evolution. Another way to start CEE is when a star on an eccentric orbit grazes its companion. Each grazing ejects a little bit of mass and tightens the orbit.
The transient brightening associated with the dynamical phase of CEE can reveal new information about the progenitor binary system, the mechanism of its instability, and the surrounding medium. To successfully model these transients, we need incorporate a number of physical effects such as recombination and ionization of various elements, formation of dust and molecules, and transport of radiation inside this environment.
Finally, dynamical interactions inside CEE eventually get weaker and the system evolution slows down. Further evolution includes interplay between the binary orbit and the remaining, expanding gas. A number of different phenomena can play a role in this late phase, in particular magnetic fields and the possibility of collimated bipolar outflows. Our goal here was to perform dedicated multi-dimensional simulations of this phase and link them to preceding dynamical evolution and observed phenomena.
We studied the stability of mass transfer in binary stars by developing one-dimensional model of the process. We estimated uncertainties in calculating this process and established path to further improvements of the model. We investigated how changes to the internal structure of a star in a binary due to binary processes influence the subsequent common envelope evolution. We performed three-dimensional simulations of a grazing encounter of an neutron star or black hole with an evolved red supergiant. We predicted shape and timescale of asymmetric mass ejection due to dust formation and radiation pressure, which might be identified in observations of evolved stars.
We implemented radiation transport in a moving mesh code to study various types of transients. First, we looked at wind-reprocessed transients and tidal disruption events in centers of galaxies. Next, we applied the code to transients associated with common envelope evolution, investigating the importance of shock interactions on the luminosity and duration of the emission. We also contributed to a study combining observations of a common envelope transients, its progenitor, and binary evolution models.
We presented a comprehensive study using three-dimensional simulations of physical processes occurring during the post-dynamical inspiral of common envelope evolution. We characterized the transport of energy and angular momentum between the binary and the surrounding gas, amplification of magnetic fields, and physical processes in the inner regions including jets.
We implemented radiation transport in a moving mesh code to study various types of transients. First, we looked at wind-reprocessed transients and tidal disruption events in centers of galaxies. Next, we applied the code to transients associated with common envelope evolution, investigating the importance of shock interactions on the luminosity and duration of the emission. We also contributed to a study combining observations of a common envelope transients, its progenitor, and binary evolution models.
We presented a comprehensive study using three-dimensional simulations of physical processes occurring during the post-dynamical inspiral of common envelope evolution. We characterized the transport of energy and angular momentum between the binary and the surrounding gas, amplification of magnetic fields, and physical processes in the inner regions including jets.
There are several aspects of our results that can be considered as beyond the state of the art. First, dedicated simulations of the late phases of common envelope evolution and in-depth investigation of fluid dynamics in this situation exceeded what was done previously. Second, we conducted the first two-dimensional simulations of common envelope transients and included realistic microphysics, confirming previous semi-analytic ideas. This work opens new avenues for connecting Luminous red novae to binary evolution models and multi-dimensional simulations of common envelope evolution. Finally, we contributed to collaborative work on one common envelope transient, which was the first to present synthesis of observations and theoretical models.