A cloud of gas collapsing under gravity will fragment. We present a new theory for this process, in which layers of shocked gas fragment due to their gravitational instability. Our model explains why angular momentum ...A cloud of gas collapsing under gravity will fragment. We present a new theory for this process, in which layers of shocked gas fragment due to their gravitational instability. Our model explains why angular momentum does not inhibit the collapse process. The theory predicts that the fragmentation process produces objects which are significantly smaller than most stars, implying that accretion onto the fragments plays an essential role in determining the initial masses of stars. This prediction is also consistent with the hypothesis that planets can be produced by gravitational collapse.展开更多
Total Routhian surface （TRS） calculations for even-even N = 76 isotones with 54 ≤ Z ≤ 68 have been performed in three-dimensional （β2,γ,β4） deformation space. Calculated results of the equilibrium deformation...Total Routhian surface （TRS） calculations for even-even N = 76 isotones with 54 ≤ Z ≤ 68 have been performed in three-dimensional （β2,γ,β4） deformation space. Calculated results of the equilibrium deformations are presented and compared with other theoretical predictions and available experimental data. The behavior of collective angular momentum shows the neutron rotation-alignment is preferred in the lighter N = 76 isotones, while for the heavier ones the proton alignment is favored. Moreover, multi-pair nucleon alignments and their competition （e.g., in 144Er） are predicted. It is pointed out that these nuclei in the N=76 isotonic chain exhibit triaxiality or γ softness in high-spin states as well as ground states. Based on deformation-energy curves with respect to axial and non-axial quadrupole deformations, the shape instabilities are evaluated in detail and predicted, particularly in γ direction. Such instabilities are also supported by the odd- and even-spin level staggering of the observed γ bands, which is usually used to distinguish between y-rigid and γ-soft asymmetry.展开更多
文摘A cloud of gas collapsing under gravity will fragment. We present a new theory for this process, in which layers of shocked gas fragment due to their gravitational instability. Our model explains why angular momentum does not inhibit the collapse process. The theory predicts that the fragmentation process produces objects which are significantly smaller than most stars, implying that accretion onto the fragments plays an essential role in determining the initial masses of stars. This prediction is also consistent with the hypothesis that planets can be produced by gravitational collapse.
基金Supported by National Natural Science Foundation of China(10805040,11175217)Foundation and Advanced Technology Rese Program of Henan Province(132300410125)S&T Research Key Program of Henan Province Education Department(13A140667)
文摘Total Routhian surface （TRS） calculations for even-even N = 76 isotones with 54 ≤ Z ≤ 68 have been performed in three-dimensional （β2,γ,β4） deformation space. Calculated results of the equilibrium deformations are presented and compared with other theoretical predictions and available experimental data. The behavior of collective angular momentum shows the neutron rotation-alignment is preferred in the lighter N = 76 isotones, while for the heavier ones the proton alignment is favored. Moreover, multi-pair nucleon alignments and their competition （e.g., in 144Er） are predicted. It is pointed out that these nuclei in the N=76 isotonic chain exhibit triaxiality or γ softness in high-spin states as well as ground states. Based on deformation-energy curves with respect to axial and non-axial quadrupole deformations, the shape instabilities are evaluated in detail and predicted, particularly in γ direction. Such instabilities are also supported by the odd- and even-spin level staggering of the observed γ bands, which is usually used to distinguish between y-rigid and γ-soft asymmetry.
