טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentShiber Sagiv
SubjectThe Role of Energetic Jets in Late Stages of Stellar
Evolution
DepartmentDepartment of Physics
Supervisor Professor Noam Soker
Full Thesis textFull thesis text - English Version


Abstract

I conduct three-dimensional hydrodynamical simulations of a secondary star that launches jets while orbiting the envelope of a giant star, in order to study the effects of jets on the grazing envelope evolution (GEE) and the common envelope evolution (CEE). I perform these simulations under the assumption that the secondary star accretes envelope gas via an accretion disk that launches the jets.

According to binary evolution theories, in a CEE a drag force acts on a companion that orbits inside the envelope of a giant star, dissipates orbital angular momentum and deposits orbital energy in the envelope that will eventually unbind the envelope. Observations of close binary systems with an evolved compact object support this scenario. However, numerical simulations of the CEE fail to achieve the unbinding of the envelope.

Jets launched by a secondary star can aid in the envelope removal. Moreover, in some cases, jets may prevent the engulfment of the secondary star and then the system will experience a GEE instead of a CEE.

I present the first three-dimensional hydrodynamical simulations of the GEE both at the onset in which the orbit of the secondary star is circular at the giant’s surface, and while the secondary star performs a spiral-in motion into the envelope. I find that in both cases the jets inflate the envelope and eject some mass. In most of the GEE simulations the outflow has a toroidal shape accompanied by two faster rings, one ring at each side of the equatorial plane. Only simulations with narrow jets result in a descendant nebula that is bipolar. The interaction of the jets with the giant envelope is the sole cause of these outflow structures, as we do not include in these simulations the secondary star gravity and the envelope self-gravity.

To investigate the role of jets in the unbinding of the envelope, I additionally conduct novel three-dimensional hydrodynamical simulations of the CEE which include jets as well as the gravitational energy released by the inspiraling core-companion system. I find that jets unbind approximately three times as much envelope mass as identical simulations that do not include jets, and that they generate high velocity outflows in the polar directions.

My results show that jets can play a crucial role in the ejection of the common envelope and in shaping bipolar outflows.