哈勃拍摄的经典螺旋星系

This NASA/ESA Hubble Space Telescope image treats viewers to a wonderfully detailed snapshot of the spiral galaxy NGC 3430 that lies 100 million light-years from Earth in the constellation Leo Minor. Several other galaxies, located relatively nearby to this one, are just beyond the frame of this image; one is close enough that gravitational interaction is driving some star formation in NGC 3430 — visible as bright-blue patches near to but outside of the galaxy’s main spiral structure. This fine example of a galactic spiral holds a bright core from which a pinwheel array of arms appears to radiate outward. Dark dust lanes and bright star-forming regions help define these spiral arms.

NGC 3430’s distinct shape may be one reason why astronomer Edwin Hubble used to it to help define his classification of galaxies. Namesake of the Hubble Space Telescope, Edwin Hubble authored a paper in 1926 that outlined the classification of some four hundred galaxies by their appearance — as either spiral, barred spiral, lenticular, elliptical, or irregular. This straightforward typology proved extremely influential, and the detailed schemes astronomers use today are still based on Edwin Hubble’s work. NGC 3430 itself is a spiral lacking a central bar with open, clearly defined arms — classified today as an SAc galaxy.

Image credit: ESA/Hubble & NASA, C. Kilpatrick

这张NASA/ESA哈勃太空望远镜拍摄的图像为观众提供了一个非常详细的螺旋星系NGC 3430的快照，它位于小狮子座，距离地球1亿光年。其他几个星系，位于这个星系附近，就在这幅图像的框架之外；其中一个距离足够近，以至于引力相互作用正在推动NGC 3430中的一些恒星形成——在星系主螺旋结构附近但外部可见明亮的蓝色斑块。这是一个星系螺旋的好例子，它有一个明亮的核心，从核心向外辐射出风车状的臂阵。黑暗的尘埃带和明亮的恒星形成区域有助于定义这些旋臂。

NGC 3430独特的形状可能是天文学家埃德温·哈勃用它来帮助定义他的星系分类的一个原因。与哈勃太空望远镜同名的埃德温·哈勃在1926年发表了一篇论文，根据星系的外观对大约400个星系进行了分类——螺旋星系、棒螺旋星系、透镜状星系、椭圆星系和不规则星系。这种简单的类型学被证明极具影响力，天文学家今天使用的详细方案仍然是基于埃德温·哈勃的工作。NGC 3430本身是一个螺旋星系，缺少一个中央棒，有着开放、清晰界定的臂状结构——今天被归类为SAc星系。

影像来源: ESA/Hubble & NASA, C. Kilpatrick