2,378 research outputs found
Formation of terrestrial planets in disks evolving via disk winds and implications for the origin of the solar system's terrestrial planets
Recent three-dimensional magnetohydrodynamical simulations have identified a
disk wind by which gas materials are lost from the surface of a protoplanetary
disk, which can significantly alter the evolution of the inner disk and the
formation of terrestrial planets. A simultaneous description of the realistic
evolution of the gaseous and solid components in a disk may provide a clue for
solving the problem of the mass concentration of the terrestrial planets in the
solar system. We simulate the formation of terrestrial planets from planetary
embryos in a disk that evolves via magnetorotational instability and a disk
wind. The aim is to examine the effects of a disk wind on the orbital evolution
and final configuration of planetary systems. We perform N-body simulations of
sixty 0.1 Earth-mass embryos in an evolving disk. The evolution of the gas
surface density of the disk is tracked by solving a one-dimensional diffusion
equation with a sink term that accounts for the disk wind. We find that even in
the case of a weak disk wind, the radial slope of the gas surface density of
the inner disk becomes shallower, which slows or halts the type I migration of
embryos. If the effect of the disk wind is strong, the disk profile is
significantly altered (e.g., positive surface density gradient, inside-out
evacuation), leading to outward migration of embryos inside ~ 1 AU. Disk winds
play an essential role in terrestrial planet formation inside a few AU by
changing the disk profile. In addition, embryos can undergo convergent
migration to ~ 1 AU in certainly probable conditions. In such a case, the
characteristic features of the solar system's terrestrial planets (e.g., mass
concentration around 1 AU, late giant impact) may be reproduced.Comment: 8 pages, 4 figures, accepted for publication in A&
NMR relaxation of quantum spin chains in magnetic fields
We investigate NMR relaxation rates 1/T_1 of quantum spin chains in magnetic
fields. Universal properties for the divergence behavior of 1/T_1 are obtained
in the Tomonaga-Luttinger-liquid state. The results are discussed in comparison
with experimental results.Comment: 5 pages, 3 figure
CO mapping of the nuclear region of NGC 6946 and IC 342 with Nobeyama millimeter array
CO observations of nearby galaxies with nuclear active star forming regions (and starburst galaxies) with angular resolutions around 7 seconds revealed that molecular bars with a length of a few kiloparsecs have been formed in the central regions of the galaxies. The molecular bar is interpreted as part of shock waves induced by an oval or barred potential field. By shock dissipation or dissipative cloud-cloud collisions, the molecular gas gains an infall motion and the nuclear star formation activity is fueled. But the distribution and kinematics of the molecular gas in the nuclear regions, which are sites of active star formation, remain unknown. Higher angular resolutions are needed to investigate the gas in the nuclear regions. Researchers made aperture synthesis observations of the nuclear region of the late-type spiral galaxies NGC 6946 and IC 342 with resolutions of 7.6 seconds x 4.2 seconds (P.A. = 147 deg) and 2.4 seconds x 2.3 seconds (P.A. = 149 deg), respectively. The distances to NGC 6496 and IC 342 are assumed to be 5.5 Mpc and 3.9 Mpc, respectively. Researchers have found 100-300 pc nuclear gas disk and ring inside a few kpc molecular gas bars. Researchers present the results of the observations and propose a possible mechanism of active star formation in the nuclear region
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