Star Formation and Bipolar Flows

Australian Journal of Physics

Two types of mass ejection are associated with the formation of young stars: poorly collimated bipolar flows and well collimated jets. Some mechanisms which have been suggested for the driving of these flows are reviewed. These include centrifugally driven magnetised winds, magnetic pressure driven winds and bubbles driven by ionised or neutral winds. The idea that the bipolar flows are bubbles driven by a neutral wind seems attractive on both theoretical and observational grounds but the source of the neutral wind-disk or star-is uncertain. It is possible that the jets are driven by magnetic pressure or by a rapidly rotating magnetic field close to the star. However, no definitive theory exists at the present time.

The Astrophysical Journal, 2006

We develop a unified model for molecular outflows in star formation. The model incorporates essential features expected of the primary wind, which is thought to be driven magnetocentrifugally from close to the central stellar object, and the ambient core material shaped by anisotropic magnetic support. The primary wind is modeled as a toroidally magnetized fast outflow moving radially away from the origin, with an angle-dependent density distribution: a dense axial jet surrounded by a more tenuous wide-angle wind, as expected in the X-wind model. If dynamically significant magnetic fields are present, the star-forming core will settle faster along the field lines than across, forming a toroid-like structure. We approximate the structure with a singular isothermal toroid whose density distribution can be obtained analytically. The interaction of the laterally stratified wind and the ambient toroid is followed using the Zeus2D magnetohydrodynamics ( MHD) code. We find that the lobes produced by the interaction resemble many systematics observed in molecular outflows from very young stars, ranging from Class 0 to I sources. In particular, both the dense axial jet and the wide-angle wind participate in the wind-ambient interaction. In our model, the jet-and wind-driven pictures of molecular outflows are unified. We discuss the observational implications of the unified picture, including the possibility of detecting the primary jet /wind directly.

The astrophysical journal, 2023

We develop a unified model for molecular outflows in star formation. The model incorporates essential features expected of the primary wind, which is thought to be driven magnetocentrifugally from close to the central stellar object, and the ambient core material shaped by anisotropic magnetic support. The primary wind is modeled as a toroidally magnetized fast outflow moving radially away from the origin, with an angle-dependent density distribution: a dense axial jet surrounded by a more tenuous wide-angle wind, as expected in the X-wind model. If dynamically significant magnetic fields are present, the star-forming core will settle faster along the field lines than across, forming a toroid-like structure. We approximate the structure with a singular isothermal toroid whose density distribution can be obtained analytically. The interaction of the laterally stratified wind and the ambient toroid is followed using the Zeus2D magnetohydrodynamics (MHD) code. We find that the lobes produced by the interaction resemble many systematics observed in molecular outflows from very young stars, ranging from Class 0 to I sources. In particular, both the dense axial jet and the wide-angle wind participate in the wind-ambient interaction. In our model, the jet-and wind-driven pictures of molecular outflows are unified. We discuss the observational implications of the unified picture, including the possibility of detecting the primary jet /wind directly.

Protostars and Planets V, 2007

Jets and outflows from young stars are an integral part of the star formation process. A particular framework for explaining these phenomena is the X-wind theory. Since PPIV, we have made good progress in modeling the jet phenomena and their associated fundamental physical processes, in both deeply embedded Class I objects and more revealed classical T Tauri stars. In particular, we have improved the treatment of the atomic physics and chemistry for modeling jet emission, including reaction rates and interaction cross-sections, as well as ambipolar diffusion between ions and neutrals. We have broadened the original X-wind picture to include the winds driven magnetocentrifugally from the innermost disk regions. We have carried numerical simulations that follow the wind evolution from the launching surface to large, observable distances. The interaction between the magnetocentrifugal wind and a realistic ambient medium was also investigated. It allows us to generalize the shell model of Shu et al. (1991) to unify the the jet-driven and wind-driven scenarios for molecular outflow production. In addition, we review related theoretical works on jets and outflows from young stars, and make connection between theory and recent observations, particularly those from HST/STIS, VLA and SMA.

2007

The driving mechanism of jets and outflows in star formation process is studied using resistive MHD nested grid simulations. We calculated cloud evolution from the molecular cloud core to the stellar core. In the collapsing cloud core, we found two distinct flows: Low-velocity flows (sim 5 km/s) with a wide opening angle, driven from the adiabatic core, and high-velocity flows (sim 30 km/s) with good collimation, driven from the protostar. High-velocity flows are enclosed by low-velocity flows after protostar formation. The difference in the degree of collimation between the two flows is caused by the strength of the magnetic field and configuration of the magnetic field lines. The magnetic field around an adiabatic core is strong and has an hourglass configuration; therefore, flows from the adiabatic core are driven mainly by the magnetocentrifugal mechanism and guided by the hourglass-like field lines. In contrast, the magnetic field around the protostar is weak and has a straight configuration owing to Ohmic dissipation in the high-density gas region. Therefore, flows from the protostar are driven mainly by the magnetic pressure gradient force and guided by straight field lines. Differing depth of the gravitational potential between the adiabatic core and the protostar cause the difference of the flow speed. Low-velocity flows correspond to the observed molecular outflows, while high-velocity flows correspond to the observed optical jets. We suggest that the outflow and the jet are driven by different cores, rather than that the outflow being entrained by the jet.

The Astrophysical Journal, 2009

The protostellar outflow is star's first cry at the moment of birth. The outflows have indispensable role in the formation of single stars, because they carry off the excess angular momentum from the centre of the shrinking gas cloud, and permits further collapse to form a star. On the other hand, a significant fraction of stars is supposed to be born as binaries with circumbinary disk that are frequently observed. Here, we investigate the evolution of a magnetized rotating cloud using three-dimensional resistive MHD nested-grid code, and show that the outflow is driven by the circumbinary disk and has an important role even in the binary formation. After the adiabatic core formation in the collapsing cloud core, the magnetic flux is significantly removed from the centre of the cloud by the Ohmic dissipation. Since this removal makes the magnetic braking ineffective, the adiabatic core continuously acquires the angular momentum to induce fragmentation and subsequent binary formation. The magnetic field accumulates in the circumbinary disk where the removal and accretion of magnetic field are balanced, and finally drives circumbinary outflow. This result explains the spectacular morphology of some specific young stellar objects such as L1551 IRS5. We can infer that most of the bipolar molecular outflows observed by low density tracers (i.e., CO) would correspond to circumbinary or circum-multiple outflows found in this report, since most of the young stellar objects are supposed to be binaries or multiples.

Symposium - International Astronomical Union, 2004

Recent observations have revealed that young stellar objects are associated with jet-like structures and Herbig-Haro objects emitting at wavelengths ranging from optical lines to radio continua. These phenomena are similar in morphologies, and have mostly comparable energetics, dynamics, and kinematics. Probing such phenomena observed at various wavelengths with self-consistent physical and radiative processes arising within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk is a challenge for confronting theory and observation of outflows. How such early outflow phase may play a role in forming planetary materials may help solve puzzles posed by meteorites. We will discuss the relevant observations, theoretical foundations for modelling approaches, magnetic structures and dynamical effects, and the connection to the early solar system.

isara solutions, 2020

“Sustainability” is a buzzword these days, but it hasn’t always been the case. The focus on developmental activities over the years/decades has led to a massive increase in the scale of human activity. It is now sufficiently significant to affect the operations of global biogeochemical systems, and thus the future of life on earth.

Jurnal Penelitian Pendidikan Islam, 2021

This article aims to reveal the concept of Islamic religious education learning in elementary schools.In the development of primary school age children have their own characteristics, the ability to think of elementary school age children develop gradually. It needs to be understood wisely to be able to deliver successful educational goals. This research adopts a descriptive qualitative approach with library research methods. The results showed that Islamic religious education in elementary school is quite unique, if in the past the mind of the child is still imaginative and egocentric then at this time the child's mind develops towards concrete, rational and objective thinking. The scope of islamic religious education study is the Qur'an, religion, morals, fiqh /worship, and islamic cultural history. The method of education that can be applied refers to the Qurani method namely amstal method, qishah method, ibrah mauidzah method, hiwar jadali method, uswah hasanah method, a...

Ius Canonicum