The theory of spiral density waves had its origin approximately six decades ago in an attempt to reconcile the winding dilemma of material spiral arms in flattened disk galaxies. We begin with the earliest calculations of linear and nonlinear spiral density waves in disk galaxies, in which the hypothesis of quasi-stationary spiral structure (QSSS) plays a central role. The earliest success was the prediction of the nonlinear compression of the interstellar medium and its embedded magnetic field; the earliest failure, seemingly, was not detecting color gradients associated with the migration of OB stars whose formation is triggered downstream from the spiral shock front. We give the reasons for this apparent failure with an update on the current status of the problem of OB star formation, including its relationship to the feathering substructure of galactic spiral arms. Infrared images can show two-armed, grand design spirals, even when the optical and UV images show flocculent structures. We suggest how t...

中文翻译：

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螺旋密度波理论的六个十年

螺旋密度波理论起源于大约 60 年前，试图调和扁平盘状星系中物质螺旋臂的缠绕困境。我们从盘状星系中线性和非线性螺旋密度波的最早计算开始，其中准静止螺旋结构（QSSS）假设起着核心作用。最早的成功是对星际介质及其嵌入磁场的非线性压缩的预测；最早的失败似乎没有检测到与 OB 星的迁移相关的颜色梯度，它们的形成是在螺旋激波前沿下游触发的。我们给出了这种明显失败的原因，并更新了 OB 恒星形成问题的当前状态，包括它与银河旋臂羽状亚结构的关系。红外图像可以显示双臂、宏伟的设计螺旋，即使光学和紫外图像显示絮状结构。我们建议如何...