2021年11月17日

哈勃望远镜拍摄的图像显示,两个螺旋星系直接重叠在一个名为NGC 3314的星系中。有关更多详细信息,请参阅说明。

NGC 3314: When Galaxies Overlap
Image Credit:
NASA, ESA, Hubble; Processing & Copyright: William Ostling (The Astronomy Enthusiast)

Explanation: Why doesn’t the nearby galaxy create a gravitational lensing effect on the background galaxy? It does, but since both galaxies are so nearby, the angular shift is much smaller than the angular sizes of the galaxies themselves. The featured Hubble image of NGC 3314 shows two large spiral galaxies which happen to line up exactly. The foreground spiral NGC 3314a appears nearly face-on with its pinwheel shape defined by young bright star clusters. Against the glow of the background galaxy NGC 3314b, though, dark swirling lanes of interstellar dust can also be seen tracing the nearer spiral’s structure. Both galaxies appear on the edge of the Hydra Cluster of Galaxies, a cluster that is about 200 million light years away. Gravitational lens distortions are much easier to see when the lensing galaxy is smaller and further away. Then, the background galaxy may even be distorted into a ring around the nearer. Fast gravitational lens flashes due to stars in the foreground galaxy momentarily magnifying the light from stars in the background galaxy might one day be visible in future observing campaigns with high-resolution telescopes.

Tomorrow’s picture: open space


NGC 3314:当星系重叠时
影像提供:
NASA, ESA, Hubble; 影像处理与版权: William Ostling (The Astronomy Enthusiast)

说明: 为何这个较近的星系没对背景星系产生重力透镜效应? 其实有,然而这二个星系都离我们很近,重力透镜产生的影像偏移远小于二者的张角,故难以分辨。这张哈勃主题影像所呈现的NGC 3314,是在视线上几乎完美重叠的二个螺旋星系。位在前景的NGC 3314a是个正向的螺旋星系,它明亮年轻星团的排列形式,让它带着风车的外观。而在背景星系NGC 3314b的辉光衬托下,较近星系内的蜿蜒黝黑星际尘埃,亦具有明显的螺旋结构。这二个星系都是约2亿年远的长蛇星系团边缘之成员星系。作为重力透镜的星系如果较小且更遥远,它产生的效应会较明显,背景星系甚至有时会扭曲成拱较近星系的光环。此外,前景星系的恒星,对背景星系恒星所产生的短暂重力透镜亮闪,未来用高解析望远镜进行观测时或许就能见到。

明日的图片: open space

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