Star formation

About: Star formation is a research topic. Over the lifetime, 37405 publications have been published within this topic receiving 1808161 citations. The topic is also known as: astrogenesis.

Magnetized Disk-Winds and the Origin of Bipolar Outflows.

Abstract: Interstellar magnetic fields play certainly a distinct role in star formation and in galactic molecular disks These magnetic fields are, however, also a key ingredient for accretion disks around young stellar objects and in the nuclei of galaxies In these objects we find a strong observational link between accretion disks and bipolar outflows in the form of winds and jets

The burst mode of accretion and disk fragmentation in the early embedded stages of star formation

Abstract: We revisit our original papers on the burst mode of accretion by incorporating a detailed energy balance equation into a thin-disk model for the formation and evolution of circumstellar disks around low-mass protostars. Our model includes the effect of radiative cooling, viscous and shock heating, and heating due to stellar and background irradiation. Following the collapse from the prestellar phase allows us to model the early embedded phase of disk formation and evolution. During this time, the disk is susceptible to fragmentation, depending upon the properties of the initial prestellar core. Globally, we find that higher initial core angular momentum and mass content favors more fragmentation, but higher levels of background radiation can moderate the tendency to fragment. A higher rate of mass infall onto the disk than that onto the star is a necessary but not a sufficient condition for disk fragmentation. More locally, both the Toomre Q-parameter needs to be below a critical value and the local cooling time needs to be shorter than a few times the local dynamical time. Fragments that form during the early embedded phase tend to be driven into the inner disk regions and likely trigger mass accretion and luminosity bursts that are similar in magnitude to FU-Orionis-type or EX-Lupi-like events. Disk accretion is shown to be an intrinsically variable process, thanks to disk fragmentation, nonaxisymmetric structure, and the effect of gravitational torques. The additional effect of a generic α-type viscosity acts to reduce burst frequency and accretion variability, and is likely to not be viable for values of α significantly greater than 0.01.

Recent star formation in the extreme outer disk of M83

Abstract: Ultraviolet imaging with the Galaxy Evolution Explorer (GALEX) has revealed an extensive sample of UV-bright stellar complexes in the extreme outer disk of M83, extending to about 4 times the radius at which the majority of H II regions are detected (R_H II = 5´.1, or 6.6 kpc). These sources are typically associated with large-scale filamentary H I structures in the warped outer disk of M83 and are distributed beyond the galactocentric radii at which molecular interstellar medium has yet been detected. We present measured properties of these stellar complexes, including far-UV and near-UV magnitudes and local gas surface density. Only a subset of the outer-disk UV sources have corresponding H II regions detected in Hα imaging, consistent with a sample of mixed age in which some sources are a few megayears old and others are much more evolved (~10^8 yr).

Filamentary accretion flows in the embedded serpens south protocluster

Abstract: One puzzle in understanding how stars form in clusters is the source of mass—is all of the mass in place before the first stars are born, or is there an extended period when the cluster accretes material which can continuously fuel the star formation process? We use a multi-line spectral survey of the southern filament associated with the Serpens South embedded cluster-forming region in order to determine if mass is accreting from the filament onto the cluster, and whether the accretion rate is significant. Our analysis suggests that material is flowing along the filament's long axis at a rate of ~30 M ☉ Myr–1 (inferred from the N2H+ velocity gradient along the filament), and radially contracting onto the filament at ~130 M ☉ Myr–1 (inferred from HNC self-absorption). These accretion rates are sufficient to supply mass to the central cluster at a similar rate to the current star formation rate in the cluster. Filamentary accretion flows may therefore be very important in the ongoing evolution of this cluster.

Diffuse infrared emission from the galaxy. I: Solar neighborhood

Abstract: A large-scale study of the infrared emission originating in the solar neighborhood based on IRAS data is presented. Away from heating sources and outside molecular clouds, the infrared emission from the ISM is well-correlated with the column density of H I gas. The interstellar radiation field and the dust abundance are roughly uniform on scales of the order of 100 pc. The extinction in the polar caps is discussed, and the origin of the infrared emission from the solar neighborhood is investigated. It is shown that stars younger than a few 100 million yr are responsible for two-thirds of the infrared emission from the solar neighborhood, but that most of this emission comes from interstellar matter not associated with current star formation. The correlation between infrared and radio-continuum fluxes of galaxies breaks down on the scale of a few hundred pc around regions of star formation. 81 references.