Unexpected Dynamical Instabilities in Differentially Rotating Neutron Stars
| Autor: | Joel E. Tohline, Shangli Ou |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Physics
Equation of state Range (particle radiation) 010308 nuclear & particles physics Stability criterion Astrophysics (astro-ph) FOS: Physical sciences Astronomy and Astrophysics Radius Astrophysics Polytropic process 01 natural sciences Resonance (particle physics) Instability Neutron star Space and Planetary Science 0103 physical sciences Astrophysics::Solar and Stellar Astrophysics Astrophysics::Earth and Planetary Astrophysics 010303 astronomy & astrophysics Astrophysics::Galaxy Astrophysics |
| Zdroj: | The Astrophysical Journal. 651:1068-1078 |
| ISSN: | 1538-4357 0004-637X |
| Popis: | A one-armed spiral instability has been found to develop in differentially rotating stellar models that have a relatively stiff, $n=1$ polytropic equation of state and a wide range of rotational energies. This suggests that such instabilities can arise in neutron stars that are differentially, although not necessarily rapidly, rotating. The instability seems to be directly triggered by the presence of a corotation resonance inside the star. Our analysis also suggests that a resonant cavity resulting from a local minimum in the radial vortensity profile of the star plays an important role in amplifying the unstable mode. Hence, it appears as through this instability is closely related to the so-called ``Rossby wave instability'' \citep{LLCN99} that has been found to arise in accretion disks. In addition to the one-armed ($m=1$) spiral mode, we have found that higher-order ($m = 2$ and $m=3$) nonaxisymmetric modes also can become unstable if corotation points that resonate with the eigenfrequencies of these higher-order modes also appear inside the star. The growth rate of each mode seems to depend on the location of its corotation radius with respect to the vortensity profile (or on the depth of its corotation radius inside the vortensity well). The existence of such instabilities makes the stability criterion for differentially rotating neutron stars non-unique. Also, the gravitational-waves emitted from such unstable systems generally will not have a monochromatic frequency spectrum. Accepted by ApJ, minor modifications added in |
| Databáze: | OpenAIRE |
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