Astronomy Picture of the Day

Explanation: What are five closely grouped galaxies doing in this image? The grouping is commonly known as Stephan's Quintet. Four of the galaxies show essentially the same redshift suggesting that they are at the same distance from us. The large bluish spiral below and left of center actually has a smaller redshift than the others, indicating it is much closer. It is probably a foreground object which happens to lie along the line of sight to the more distant galaxies. Of the four distant galaxies, three seem to be colliding, showing serious distortions due to gravitational tidal forces. The fourth is a normal appearing elliptical galaxy (at the lower right edge of the field). Recent results suggest that collisions play an important role in the life cycles of galaxies.

在這張影像裡，這5個聚在一起的星系在做什麼呢？這群天體常稱為斯蒂芬五重星系。 其中4個星系的紅移基本相同，這代表它們與我們的距離相同。 影像中下左側的較大泛藍螺旋星系，其實具有比其他星系更小的紅移，這表示它與我們的距離要近很多。 因此，它可能是一個前景天體，碰巧和較遠的星系在同一視線上。 這4個位於遠處的星系之中，有3個似乎正在發生碰撞，並展現出因重力潮汐力而產生的嚴重扭曲。 第4個則是一個外觀正常的橢圓星系（在視野的右下緣）。 最近的研究結果顯示，碰撞在星系的生命周期中扮演著重要的角色。