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<p>The coupling is established analytically between the natural oscillations of stars normal to the mean horizontal plane and periodic changes in the excitation force in a rotationally flattened galactic disk using a linear perturbation framework. The nonaxisymmetric gravitational potential of a density-wave bar may cause these changes in this ‘pumping’ force. The excitation of out-of-plane oscillating motion with an amplitude exponentially increasing with time via parametric resonance interaction between stars and a bar is considered for the formation of the boxy/peanut-shaped bulges (an X-structure of stars crossing at the center of the system) often observed in disk galaxies, even in isolation, as well as in the Galaxy. A scenario involving this resonant interaction accounts for both the vertically short <InlineEquation ID="IEq1"> <EquationSource Format="MATHML"><math> <mo>≲</mo> <mn>1</mn> </math></EquationSource> <EquationSource Format="TEX">$\lesssim 1$</EquationSource> </InlineEquation> kpc boxy/peanut-shaped features and a <InlineEquation ID="IEq2"> <EquationSource Format="MATHML"><math> <mo>∼</mo> <mn>1</mn> </math></EquationSource> <EquationSource Format="TEX">$\sim 1$</EquationSource> </InlineEquation> Gyr time delay between when the bars form and vertically thicken.</p>

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Parametric resonance scenario for peanut bulge formation in rotating galactic stellar disks

  • 期刊论文

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  • 发表日期：

    2026年2月25日

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  • Evgeny Griv,
  • Asher Yahalom

摘要

The coupling is established analytically between the natural oscillations of stars normal to the mean horizontal plane and periodic changes in the excitation force in a rotationally flattened galactic disk using a linear perturbation framework. The nonaxisymmetric gravitational potential of a density-wave bar may cause these changes in this ‘pumping’ force. The excitation of out-of-plane oscillating motion with an amplitude exponentially increasing with time via parametric resonance interaction between stars and a bar is considered for the formation of the boxy/peanut-shaped bulges (an X-structure of stars crossing at the center of the system) often observed in disk galaxies, even in isolation, as well as in the Galaxy. A scenario involving this resonant interaction accounts for both the vertically short ≲ 1 $\lesssim 1$ kpc boxy/peanut-shaped features and a ∼ 1 $\sim 1$ Gyr time delay between when the bars form and vertically thicken.