Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complex...Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complexity of the physics that drives their formation within molecular clouds. In this article theoretical modelling of the lowest possible mass of the cloud needed for collapse and the core accretion rate has been presented for the molecular cloud collapsing under its gravity. In many of previous studies the critical mass of star forming cloud under its gravity has been modelled using kinetic energy and gravitational potential energy. However, we test the effect of thermodynamic efficiency factor together with other physical processes in describing the critical mass, and controlling or triggering the rate of mass falling onto the central core. Assuming that, the ratio of radiation luminosity to gravitational energy released per unit time of the collapsing MC is less than unity. Following this conceptual framework we have formulated the critical mass and the core accretion rate of the self-gravitating molecular cloud.展开更多
We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Sol...We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 〈 10^（-7.4）M_☉yr^（-1）, only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes（tandem planet formation regime and dispersed planet formation regime）, in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early.展开更多
In the tandem planet formation regime,planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability（MRI）.We found that tandem planet fo...In the tandem planet formation regime,planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability（MRI）.We found that tandem planet formation can reproduce the solid component distribution of the Solar System and tends to produce a smaller number of large planets through continuous pebble flow into the planet formation sites.In the present paper,we investigate the dependence of tandem planet formation on the vertical magnetic field of the protoplanetary disk.We calculated two cases of BZ 3.4 × 10^-3 G and BZ = 3.4 × 10^-5 G at 100 AU as well as the canonical case of BZ = 3.4 × 10^-4 G.We found that tandem planet formation holds up well in the case of the strong magnetic field（BZ 3.4 × 10^-3 G）.On the other hand,in the case of a weak magnetic field（BZ= 3.4 × 10^-5 G） at 100 AU,a new regime of planetary growth is realized：the planets grow independently at different places in the dispersed area of the MRl-suppressed region of r-8-30 AU at a lower accretion rate of M 〈 10^-7.4M⊙yr^-1.We call this the ＂dispersed planet formation＂ regime.This may lead to a system with a larger number of smaller planets that gain high eccentricity through mutual collisions.展开更多
We present a new united theory of planet formation,which includes magneto-rotational instability（MRl） and porous aggregation of solid particles in a consistent way.We show that the ＂tandem planet formation＂ regime...We present a new united theory of planet formation,which includes magneto-rotational instability（MRl） and porous aggregation of solid particles in a consistent way.We show that the ＂tandem planet formation＂ regime is likely to result in solar system-like planetary systems.In the tandem planet formation regime,planetesimals form at two distinct sites：the outer and inner edges of the MRl suppressed region.The former is likely to be the source of the outer gas giants,and the latter is the source for the inner volatile-free rocky planets.Our study spans disks with a various range of accretion rates,and we find that tandem planet formation can occur for M = 10^7.3- 10^-6.9Myr^-1.The rocky planets form between 0.4-2 AU,while the icy planets form between 6-30 All;no planets form in 2-6 AU region for any accretion rate.This is consistent with the gap in the solid component distribution in the solar system,which has only a relatively small Mars and a very small amount of material in the main asteroid belt from 2-6 AU.The tandem regime is consistent with the idea that the Earth was initially formed as a completely volatile-free planet.Water and other volatile elements came later through the accretion of icy material by occasional inward scattering from the outer regions.Reactions between reductive minerals,such as schreibersite（Fe-jP）,and water are essential to supply energy and nutrients for primitive life on Earth.展开更多
We consider the existence of a neutron star magnetic field by the detected cyclotron lines. We collected data on nine sources of high-mass X-ray binaries with supergiant companions as a test case for our model, to dem...We consider the existence of a neutron star magnetic field by the detected cyclotron lines. We collected data on nine sources of high-mass X-ray binaries with supergiant companions as a test case for our model, to demonstrate their distribution and evolution. The wind velocity, spin period and magnetic field strength are studied under different mass loss rates. In our model, correlations between mass-loss rate and wind velocity are found and can be tested in further observations. We examine the parameter space where wind accretion is allowed, avoiding the barrier of rotating magnetic fields, with robust data on the magnetic field of neutron stars. Our model shows that most sources(six of nine systems) can be fed by the wind with relatively slow velocity, and this result is consistent with previous predictions. In a few sources,our model cannot fit the standard wind accretion scenario. In these peculiar cases, other scenarios(disk formation, partial Roche lobe overflow) should be considered. This would provide information about the evolutionary tracks of various types of binaries, and thus exhibit a clear dichotomy behavior in wind-fed X-ray binary systems.展开更多
We investigate the effects of the cooling function in the formation of clumps of protoplanetary disks using two-dimensional smoothed particle hydrody- namic simulations. We use a simple prescription for the cooling ra...We investigate the effects of the cooling function in the formation of clumps of protoplanetary disks using two-dimensional smoothed particle hydrody- namic simulations. We use a simple prescription for the cooling rate of the flow, du/dt = -u/τcool, where u and %ool are the internal energy and cooling timeseale, respectively. We assume the ratio of local＇cooling to dynamical timescale, Ωτcool =β, to be a constant and also a function of the local temperature. We found that for the constantβ and γ = 5/3, fragmentation occurs only forβ ≤ 7. However, in the case ofβ having temperature dependence and γ = 5/3, fragmentation can also occur for larger values ofβ. By increasing the temperature dependence of the cooling timescale, the mass accretion rate decreases, the population of clumps/fragments increases, and the clumps/fragments can also form in the smaller radii. Moreover, we found that the clumps can form even in a low mass accretion rate, ≤10-7M⊙yr-1, in the case of temperature-dependentβ. However, clumps form with a larger mass accretion rate, 〉 10-7M⊙ yr-1, in the case of constantβ.展开更多
文摘Understanding how stars form in molecular clouds is one of the ongoing research areas in astrophysics. Star formation is the fundamental process to which our current understanding remains incomplete due to the complexity of the physics that drives their formation within molecular clouds. In this article theoretical modelling of the lowest possible mass of the cloud needed for collapse and the core accretion rate has been presented for the molecular cloud collapsing under its gravity. In many of previous studies the critical mass of star forming cloud under its gravity has been modelled using kinetic energy and gravitational potential energy. However, we test the effect of thermodynamic efficiency factor together with other physical processes in describing the critical mass, and controlling or triggering the rate of mass falling onto the central core. Assuming that, the ratio of radiation luminosity to gravitational energy released per unit time of the collapsing MC is less than unity. Following this conceptual framework we have formulated the critical mass and the core accretion rate of the self-gravitating molecular cloud.
基金partly supported by Grant-in-Aid for Scientific Research on Innovative Areas Number 26106006
文摘We studied the particle growth in a protoplanetary disk in a high-ionization environment and found that icy planet formation is inactive for a disk with an ionization rate 100 times higher than that of the present Solar System. In particular, in the case of M 〈 10^（-7.4）M_☉yr^（-1）, only rocky planet formation occurs. In such a case, all the solid materials in the disk drift inward, eventually reach the inner MRI front,and accumulate there. They form a dense, thin sub-disk of solid particles, which undergoes gravitational instability to form rocky planetesimals. The planetesimals rapidly grow into a planet through pebble accretion. Consequently, rocky planets tend to be much larger than planets formed through other regimes（tandem planet formation regime and dispersed planet formation regime）, in which icy planet formation actively takes place. These rocky planets may evolve into hot Jupiters if they grow fast enough to the critical core mass of the runaway gas accretion before the dispersal of the disk gas, or they may evolve into super-Earths if the gas dispersed sufficiently early.
基金supported by a Grant-in-Aid for Scientific Research on Innovative Areas(Grant No.26106006)
文摘In the tandem planet formation regime,planets form at two distinct sites where solid particles are densely accumulated due to the on/off state of the magnetorotational instability（MRI）.We found that tandem planet formation can reproduce the solid component distribution of the Solar System and tends to produce a smaller number of large planets through continuous pebble flow into the planet formation sites.In the present paper,we investigate the dependence of tandem planet formation on the vertical magnetic field of the protoplanetary disk.We calculated two cases of BZ 3.4 × 10^-3 G and BZ = 3.4 × 10^-5 G at 100 AU as well as the canonical case of BZ = 3.4 × 10^-4 G.We found that tandem planet formation holds up well in the case of the strong magnetic field（BZ 3.4 × 10^-3 G）.On the other hand,in the case of a weak magnetic field（BZ= 3.4 × 10^-5 G） at 100 AU,a new regime of planetary growth is realized：the planets grow independently at different places in the dispersed area of the MRl-suppressed region of r-8-30 AU at a lower accretion rate of M 〈 10^-7.4M⊙yr^-1.We call this the ＂dispersed planet formation＂ regime.This may lead to a system with a larger number of smaller planets that gain high eccentricity through mutual collisions.
基金supported by Grant-in-Aid for Scientific Research on Innovative Areas Number 26106006
文摘We present a new united theory of planet formation,which includes magneto-rotational instability（MRl） and porous aggregation of solid particles in a consistent way.We show that the ＂tandem planet formation＂ regime is likely to result in solar system-like planetary systems.In the tandem planet formation regime,planetesimals form at two distinct sites：the outer and inner edges of the MRl suppressed region.The former is likely to be the source of the outer gas giants,and the latter is the source for the inner volatile-free rocky planets.Our study spans disks with a various range of accretion rates,and we find that tandem planet formation can occur for M = 10^7.3- 10^-6.9Myr^-1.The rocky planets form between 0.4-2 AU,while the icy planets form between 6-30 All;no planets form in 2-6 AU region for any accretion rate.This is consistent with the gap in the solid component distribution in the solar system,which has only a relatively small Mars and a very small amount of material in the main asteroid belt from 2-6 AU.The tandem regime is consistent with the idea that the Earth was initially formed as a completely volatile-free planet.Water and other volatile elements came later through the accretion of icy material by occasional inward scattering from the outer regions.Reactions between reductive minerals,such as schreibersite（Fe-jP）,and water are essential to supply energy and nutrients for primitive life on Earth.
基金the Abdul Hamed Shoman Foundation (Grant No. 6/2017) for supporting this projectsupported by the JSPS KAKENHI (Grant No. 18K03706)+1 种基金supported by the National Key R&D Program of China (2016YFA0400801)the National Natural Science Foundation of China (Grant No. U1838201)
文摘We consider the existence of a neutron star magnetic field by the detected cyclotron lines. We collected data on nine sources of high-mass X-ray binaries with supergiant companions as a test case for our model, to demonstrate their distribution and evolution. The wind velocity, spin period and magnetic field strength are studied under different mass loss rates. In our model, correlations between mass-loss rate and wind velocity are found and can be tested in further observations. We examine the parameter space where wind accretion is allowed, avoiding the barrier of rotating magnetic fields, with robust data on the magnetic field of neutron stars. Our model shows that most sources(six of nine systems) can be fed by the wind with relatively slow velocity, and this result is consistent with previous predictions. In a few sources,our model cannot fit the standard wind accretion scenario. In these peculiar cases, other scenarios(disk formation, partial Roche lobe overflow) should be considered. This would provide information about the evolutionary tracks of various types of binaries, and thus exhibit a clear dichotomy behavior in wind-fed X-ray binary systems.
文摘We investigate the effects of the cooling function in the formation of clumps of protoplanetary disks using two-dimensional smoothed particle hydrody- namic simulations. We use a simple prescription for the cooling rate of the flow, du/dt = -u/τcool, where u and %ool are the internal energy and cooling timeseale, respectively. We assume the ratio of local＇cooling to dynamical timescale, Ωτcool =β, to be a constant and also a function of the local temperature. We found that for the constantβ and γ = 5/3, fragmentation occurs only forβ ≤ 7. However, in the case ofβ having temperature dependence and γ = 5/3, fragmentation can also occur for larger values ofβ. By increasing the temperature dependence of the cooling timescale, the mass accretion rate decreases, the population of clumps/fragments increases, and the clumps/fragments can also form in the smaller radii. Moreover, we found that the clumps can form even in a low mass accretion rate, ≤10-7M⊙yr-1, in the case of temperature-dependentβ. However, clumps form with a larger mass accretion rate, 〉 10-7M⊙ yr-1, in the case of constantβ.
