scholarly journals Improved Secular Stability Limits for Rotating White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 43-47
Author(s):  
R. H. Durisen ◽  
J. N. Imamura
Keyword(s):  
Kinetic Energy ◽  
Gravitational Radiation ◽  
Time Scale ◽  
White Dwarfs ◽  
Gravitational Energy ◽  
Dissipative Processes ◽  
Stability Limits ◽  
Special Case ◽  
Nonrotating Frame

In the special case of the Maclaurin spheroids, it has been known for some time that the m = 2 barlike modes become secularly unstable for t ≡ T/IWI ≥ 0.1376 where T is the total rotational kinetic energy and W is the total gravitational energy of the spheroid. “Secular” here means that the instability depends on dissipative processes and grows on a long dissipative time scale. In particular, the Dedekind-like bar mode, which has zero eigenfrequency at t = 0.1376 as viewed in the nonrotating frame, is unstable due to gravitational radiation (Chandrasekhar 1970).

scholarly journals The Method of Virtual Quanta and Gravitational Radiation

1974 ◽  
Vol 64 ◽  
pp. 16-16
Author(s):  
Richard A. Matzner ◽  
Yavuz Nutku
Keyword(s):  
Test Particle ◽  
Gravitational Radiation ◽  
Plane Waves ◽  
Test Body ◽  
Gravitational Energy ◽  
Fourier Component ◽  
Radiative Loss ◽  
Newtonian Type ◽  
Moving Particle

We extend the Weizsäcker-Williams method to the domain of gravitational encounters and correlate collision problems with the corresponding interaction of gravitational radiation. To an ultra-relativistic test particle the field of a Schwarzschild mass appears as a pulse of gravitational plane waves. We consider the scattering of each Fourier component, virtual quanta, by the Newtonian-type field of the test body. The scattered flux at infinity gives us the radiative loss of gravitational energy by a rapidly moving particle.

scholarly journals On turbulent mixing

1984 ◽  
Vol 105 ◽  
pp. 519-521
Author(s):  
Ian W. Roxburgh
Keyword(s):  
Angular Momentum ◽  
Differential Rotation ◽  
Turbulent Mixing ◽  
Time Scale ◽  
Meridional Circulation ◽  
Neutrino Flux ◽  
Gravitational Energy ◽  
Solar Neutrino Flux ◽  
Angular Momentum Loss ◽  
Image Position

Several authors (myself included!) have suggested that turbulent mixing takes place in some, if not all, stars, and in particular that such mixing can explain the low solar neutrino flux. This turbulence is thought to be caused by differential rotation produced by braking due to angular momentum loss in a stellar wind, and/or to the effect of meridional circulation currents in redistributing angular momentum. Whilst such instabilities may exist even in the presence of a stabilizing distribution of chemical composition, they do not necessarily cause mixing. To be effective in mixing, the energy available to the instability be it differential rotation or any other mechanism, has to be sufficient to lift the helium rich matter in the interior of the star to the outer regions. This requires where Erot is the kinetic energy in rotation, Eg the gravitational energy, τth the thermal time scale and τnuc the nuclear evolution time scale of the star.

scholarly journals Evolution of Contact Systems

1976 ◽  
Vol 73 ◽  
pp. 337-341
Author(s):  
O. Vilhu ◽  
T. Rahunen
Keyword(s):  
Time Scale ◽  
Gravitational Energy ◽  
Evolutionary Track ◽  
Crucial Importance ◽  
The Third ◽  
Massive Component ◽  
Long Time ◽  
Contact Binaries ◽  
Mass Transfers ◽  
Evolution Proceeds

The evolution of contact binaries with common convective envelopes has been studied. Gravitational energy due to the mass exchange is taken into account in both stars, which turned out to be of crucial importance. Three qualitatively different evolutionary tracks have been found for an initial system 1.2M⊙ + 1.0M⊙. One of these corresponds to those found by Moss (1971), in which mass transfers, on a long time scale (≈5 × 108 yr), from the less massive component to the heavier. The second is similar to the solution found by Hazlehurst and Meyer-Hofmeister (1973), in which the evolution proceeds towards equal masses in a much shorter time scale (≈2 × 107 yr). The third possibility is similar to the first one, but its time scale is 10 times shorter (≈5 × 107 yr). The true evolutionary track may well oscillate randomly around the different solutions (rapid period changes).

scholarly journals Star–disc alignment in the protoplanetary discs: SPH simulation of the collapse of turbulent molecular cloud cores

2020 ◽  
Vol 492 (4) ◽  
pp. 5641-5654 ◽  
Author(s):  
Daisuke Takaishi ◽  
Yusuke Tsukamoto ◽  
Yasushi Suto
Keyword(s):  
Time Scale ◽  
Molecular Cloud ◽  
Three Dimensional ◽  
Gravitational Energy ◽  
Circumstellar Envelope ◽  
Rotation Axes ◽  
Particle Hydrodynamics ◽  
Disc Rotation ◽  
Cloud Cores ◽  
Sph Simulation

ABSTRACT We perform a series of three-dimensional smoothed particle hydrodynamics (SPH) simulations to study the evolution of the angle between the protostellar spin and the protoplanetary disc rotation axes (the star–disc angle ψsd) in turbulent molecular cloud cores. While ψsd at the protostar formation epoch exhibits broad distribution up to ∼130°, ψsd decreases (≲ 20°) in a time-scale of ∼104 yr. This time-scale of the star–disc alignment, talignment, corresponds basically to the mass doubling time of the central protostar, in which the protostar forgets its initial spin direction due to the mass accretion from the disc. Values of ψsd both at t = 102 yr and t = 105 yr after the protostar formation are independent of the ratios of thermal and turbulent energies to gravitational energy of the initial cloud cores: α = Ethermal/|Egravity| and γturb = Eturbulence/|Egravity|. We also find that a warped disc is possibly formed by the turbulent accretion flow from the circumstellar envelope.

scholarly journals Equilibration dynamics in nuclear reactions

2019 ◽  
Vol 223 ◽  
pp. 01066
Author(s):  
A.S. Umar ◽  
C. Simenel ◽  
S. Ayik ◽  
K. Godbey
Keyword(s):  
Kinetic Energy ◽  
Time Scales ◽  
Time Scale ◽  
Nuclear Reactions ◽  
Total Kinetic Energy ◽  
Equilibration Time

We discuss the equilibration dynamics and time–scales for various quantities that are connected to the experimentally observable entities. These include the study of mass, isospin, and total kinetic energy (TKE)equilibration time–scales as well as the time–scale for fluctuations.

Gravitational Radiation From Differentialy Rotating And Oscillating White Dwarfs

2007 ◽  
Author(s):  
K. M. Shahabasyan ◽  
M. K. Shahabasyan ◽  
D. M. Sedrakyan
Keyword(s):  
Gravitational Radiation ◽  
White Dwarfs

scholarly journals Critical Mass for Merging in Double White Dwarfs

1989 ◽  
Vol 114 ◽  
pp. 450-453
Author(s):  
Izumi Hachisu ◽  
Mariko Kato
Keyword(s):  
Mass Transfer ◽  
Gravitational Radiation ◽  
White Dwarf ◽  
Binary Stars ◽  
White Dwarfs ◽  
Radiation Effect ◽  
Critical Mass ◽  
Mass Transfer Rate ◽  
Roche Lobe ◽  
Common Envelope

We examine whether or not double white dwarfs are ultimately merging into one body. It has been argued that such a double white dwarf system forms from some intermediate-mass binary stars and will merge due to the gravitational radiation which decreases the separation of binary. After filling the inner critical Roche lobe, the less massive component begins to transfer its mass to the more massive one. When the mass transfer rate exceeds a some critical value, a common envelope is formed. If the common envelope is hydrostatic, the mass transfer is tuned up to be a some value which depends only on the white dwarf mass, radius, and the Roche lobe size. The mass transfer from the less massive to the more massive components leads the separation to increase. On the other hand, the gravitational radiation effect reduces the separation. Which effect wins determines the fate of double white dwarfs, that is, whether merging or not merging. Since the formula of the gravitational radiation effect is well known, we have studied the mass accretion rate in common envelope phase of double white dwarfs assuming the Roche lobe size is as small as 0.03 R⊙ or 0.1 R⊙.

scholarly journals EXACT NONNULL WAVELIKE SOLUTIONS TO GRAVITY WITH QUADRATIC LAGRANGIANS

1994 ◽  
Vol 09 (02) ◽  
pp. 167-179 ◽  
Author(s):  
M.D. ROBERTS
Keyword(s):  
Gravitational Radiation ◽  
Riemann Tensor ◽  
Gravitational Energy ◽  
Cross Terms ◽  
Linearized Theory ◽  
Relationship Of ◽  
The Relationship ◽  
Poynting Vectors ◽  
Derivatives Of

Solutions to gravity with quadratic Lagrangians are found for the simple case where the only nonconstant metric component is the lapse N and the Riemann tensor takes the form [Formula: see text] thus these solutions depend on cross terms in the Riemann tensor and therefore complement linearized theory where it is the derivatives of the Riemann tensor that matter. The relationship of this metric to the null gravitational radiation metric of Peres is given. Gravitational energy Poynting vectors are constructed for the solutions and one of these, based on the Lanczos tensor, supports the indication in the linearized theory that nonnull gravitational radiation can occur.

scholarly journals The Rayleigh-Taylor Instability Overturn of Supernova Cores during Bouncing and Resulting Neutrino Energy Release

1980 ◽  
Vol 5 ◽  
pp. 517-519
Author(s):  
S. A. Colgate ◽  
A. G. Petschek
Keyword(s):  
Kinetic Energy ◽  
Energy Release ◽  
Neutrino Energy ◽  
Gravitational Energy ◽  
Taylor Instability ◽  
Rotational Perturbation ◽  
Reversal Time ◽  
Sudden Release ◽  
Rayleigh Taylor Instability

We show that Rayleigh-Taylor convective overturn of the dynamically formed lepton-trapped core of a supernova is a likely outcome of three sequential events: (1) The bounce or weak reversal shock; (2) the diffusive and convective lepton release from the neutrino-sphere during a fraction of the reversal time (≌ 100 ms); and (3) the rapid (≤ 10 ms) Rayleigh-Taylor growth of the l = 2 mode of an initial rotational perturbation. The overturn releases gravitational energy corresponding to a differential trapped lepton pressure energy of 30 to 50 MeV/nucleon by P dV work in beta equilibrium in a fraction of a millisecond. The resulting kinetic energy of ≌ 7 × 1052 ergs is more than adequate to cause the observed supernova emission. Also, the sudden release of ≌ 7 × 1051 ergs of ˜ 10 MeV neutrinos from the neutrinosphere will cause adequate mass and energy ejection.

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