Kinematics of filaments in cooling flow clusters and heating by mixing

We compare a recent study of the kinematics of optical filaments in three cooling flow clusters of galaxies with previous numerical simulations of jet-inflated hot bubbles, and conclude that the velocity structure functions of the filaments better fit direct excitation by the jets than by turbulent cascade from the largest turbulent eddies. The observed velocity structure functions of the optical filaments in the three clusters are steeper than that expected from a classical cascade in turbulent dissipation. Our three-dimensional (3D) hydrodynamical simulations show that as the jets inflate bubbles in the intracluster medium (ICM), they form vortexes in a large range of scales. These vortexes might drive the ICM turbulence with eddies of over more than an order of magnitude in size. A direct excitation of turbulence by the vortexes that the jets form and the slow turbulent dissipation imply that heating the ICM by mixing with hot bubbles is more efficient than heating by turbulent dissipation.Comment: Accepted for publication in The Astrophysical Journa

Fermion Bag Solitons in the Massive Gross-Neveu and Massive Nambu-Jona-Lasinio Models in 1+1 Dimensions: Inverse Scattering Analysis

Formation of fermion bag solitons is an important paradigm in the theory of hadron structure. We report here on our non-perturbative analysis of this phenomenon in the 1+1 dimensional massive Gross-Neveu model, in the large $N$ limit. Our main result is that the extremal static bag configurations are reflectionless, as in the massless Gross-Neveu model. Explicit formulas for the profiles and masses of these solitons are presented. We also present a particular type of self-consistent reflectionless solitons which arise in the massive Nambu-Jona-Lasinio models, in the large-N limit.Comment: latex, 8 pages, no figures. Talk by JF at QFTEXT05, Barcelona, Sept. 200

Uplifted cool gas and heating by mixing in cooling flows

We analyze our earlier three-dimensional hydrodynamical numerical simulation of jet-inflated bubbles in cooling flow clusters, and find that dense gas that was not heated by the jets' activity and that resides around the hot jet-inflated bubbles can be identified as uplifted gas as observed in some clusters. During the build up of the dense gas around the hot bubble, mixing of hot bubble gas with other regions of the intracluster medium (ICM) heats the ICM. The vortices that mix the ICM with the hot bubble gas also excite shock waves, sound waves, and turbulence. Sound waves, shocks, turbulence, and uplifted gas, might be easier to detect than the mixing process and hence attract more attention, but we argue that the contributions of these processes to the heating of the ICM do not add up to the level of contribution of the mixing-heating process.Comment: Accepted for publication by Research in Astronomy and Astrophysic

Gentle heating by mixing in cooling flow clusters

We analyze three-dimensional hydrodynamical simulations of the interaction of jets and the bubbles they inflate with the intra-cluster medium (ICM), and show that the heating of the ICM by mixing hot bubble gas with the ICM operates over tens of millions of years, and hence can smooth the sporadic activity of the jets. The inflation process of hot bubbles by propagating jets forms many vortices, and these vortices mix the hot bubble gas with the ICM. The mixing, hence the heating of the ICM, starts immediately after the jets are launched, but continues for tens of millions of years. We suggest that the smoothing of the active galactic nucleus (AGN) sporadic activity by the long-lived vortices accounts for the recent finding of a gentle energy coupling between AGN heating and the ICM.Comment: Accepted for publication in Ap

Heating Cold Clumps by Jet-inflated Bubbles in Cooling Flow Clusters

We simulate the evolution of dense-cool clumps embedded in the intra-cluster medium (ICM) of cooling flow clusters of galaxies in response to multiple jet-activity cycles, and find that the main heating process of the clumps is mixing with the hot shocked jets' gas, the bubbles, while shocks have a limited role. We use the PLUTO hydrodynamical code in two dimensions with imposed axisymmetry, to follow the thermal evolution of the clumps. We find that the inflation process of hot bubbles, that appear as X-ray deficient cavities in observations, is accompanied by complicated induced vortices inside and around the bubbles. The vorticity induces efficient mixing of the hot bubbles' gas with the ICM and cool clumps, resulting in a substantial increase of the temperature and entropy of the clumps. For the parameters used by us heating by shocks barely competes with radiative cooling, even after 25 consecutive shocks excited during 0.5 Gyr of simulation. Some clumps are shaped to filamentary structure that can turn to observed optical filaments. We find that not all clumps are heated. Those that cool to very low temperatures will fall in and feed the central supermassive black hole (SMBH), hence closing the feedback cycle in what is termed the cold feedback mechanism.Comment: Accepted by MNRA

An outburst powered by the merging of two stars inside the envelope of a giant

We conduct three-dimensional hydrodynamical simulations of energy deposition into the envelope of a red giant star as a result of the merger of two close main sequence stars or brown dwarfs, and show that the outcome is a highly non-spherical outflow. Such a violent interaction of a triple stellar system can explain the formation of `messy', i.e., lacking any kind of symmetry, planetary nebulae (PNe) and similar nebulae around evolved stars. We do not simulate the merging process, but simply assume that after the tight binary system enters the envelope of the giant star the interaction with the envelope causes the two components, stars or brown dwarfs, to merge and liberate gravitational energy. We deposit the energy over a time period of about nine hours, which is about one per cent of the orbital period of the merger product around the centre of the giant star. The ejection of the fast hot gas and its collision with previously ejected mass are very likely to lead to a transient event, i.e., an intermediate luminosity optical transient (ILOT).Comment: Appeared in MNRAS, 471, 3456 (2017

Rescuing the intracluster medium of NGC 5813

We use recent X-ray observations of the intracluster medium (ICM) of the galaxy group NGC 5813 to confront theoretical studies of ICM thermal evolution with the newly derived ICM properties. We argue that the ICM of the cooling flow galaxy group NGC 5813 is more likely to be heated by mixing of post-shock jets' gas residing in hot bubbles with the ICM, than by shocks or turbulent-heating. Shocks thermalize only a small fraction of their energy in the inner regions of the cooling flow; in order to adequately heat the inner part of the ICM, they would overheat the outer regions by a large factor, leading to its ejection from the group. Heating by mixing, that was found to be much more efficient than turbulent-heating and shocks-heating, hence, rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.Comment: Accepted for publication in Research in Astronomy and Astrophysic

Energy transport by convection in the common envelope evolution

We argue that outward transport of energy by convection and photon diffusion in a common envelope evolution (CEE) of giant stars substantially reduces the fraction of the recombination energy of hydrogen and helium that is available for envelope removal. We base our estimate on the properties of an unperturbed asymptotic giant branch (AGB) spherical model, and on some simple arguments. Since during the CEE the envelope expands and energy removal by photon diffusion becomes more efficient, our arguments underestimate the escape of recombination energy. We hence strengthen earlier claims that recombination energy does not contribute much to common envelope removal. A large fraction of the energy that jets deposit to the envelope, on the other hand, might be in the form of kinetic energy of the expanding and buoyantly rising hot bubbles. These rapidly rising bubbles remove mass from the envelope. We demonstrate this process by conducting a three-dimensional hydrodynamical simulation where we deposit hot gas in the location of a secondary star that orbits inside the envelope of a giant star. Despite the fact that we do not include the large amount of gravitational energy that is released by the in-spiraling secondary star, the hot bubbles alone remove mass at a rate of about 0.1 Mo/yr, which is much above the regular mass loss rate.Comment: accepted to MNRA

Inclined jets inside a common envelope of a triple stellar system

We conduct a three-dimensional hydrodynamical simulation to study the interaction of two opposite inclined jets inside the envelope of a giant star, and find that the jets induce many vortexes inside the envelope and that they efficiently remove mass from the envelope and form a very clumpy outflow. We assume that this very rare type of interaction occurs when a tight binary system enters the envelope of a giant star, and that the orbital plane of the tight binary system and that of the triple stellar system are inclined to each other. We further assume that one of the stars of the tight binary system accretes mass and launches two opposite jets and that the jets' axis is inclined to the angular momentum axis of the triple stellar system. The many vortexes that the jets induce along the orbit of the tight binary system inside the giant envelope might play an important role in the common envelope evolution (CEE) by distributing energy in the envelope. The density fluctuations that accompany the vortexes lead to an outflow with many clumps that might facilitate the formation of dust. This outflow lacks any clear symmetry, and it might account for very rare types of `messy' planetary nebulae and `messy' nebulae around massive stars. On a broader scope, our study adds to the notion that jets can play important roles in the CEE, and that they can form a rich variety of shapes of nebulae around evolved stars.Comment: Accepted for publication in MNRA

A companion star launching jets in the wind acceleration zone of a giant star

By conducting three-dimensional (3D) hydrodynamical simulations we find that jets that a main sequence companion launches as it orbits inside the wind acceleration zone of an asymptotic giant branch (AGB) star can efficiently remove mass from that zone. We assume that during the intensive wind phase a large fraction of the gas in the acceleration zone does not reach the escape velocity. Therefore, in the numerical simulations we blow the wind with a velocity just below the escape velocity. We assume that a main sequence companion accretes mass from the slow wind via an accretion disk, and launches two opposite jets perpendicular to the equatorial plane. This novel flow interaction shows that by launching jets a companion outside a giant star, but close enough to be in the acceleration zone of a slow intensive wind, can enhance the mass loss rate from the giant by ejecting some gas that would otherwise fall back onto the giant star. The jets are bent inside the wind acceleration zone and eject mass in a belt on the two sides of the equatorial plane. The jet-wind interaction contains instabilities that mix shocked jets' gas with the wind, leading to energy transfer from the jets to the wind. As well, our new simulations add to the rich variety of jet-induced outflow morphologies from evolved stars.Comment: Accepted for publication in The Astrophysical Journa