Whirlpool Galaxy, M51a

The Whirlpool Galaxy, M51a and companion M51b
(credit NASA, ESA, S. Beckwith (STSci), and the Hubble Heritage Team(STSci/AURA),The Hubble Space Telescope ACS.)

The Whirlpool Galaxy is one of the most famous galaxies in the sky, having been discovered by Charles Messier in 1774 and designated in the Messier catalog as M51. In 1781 the companion galaxy, NGC 5195, was discovered by Pierre Mechain. The Whirlpool Galaxy and its companion are often designated M51a and M51b. The distance to the galaxy is about 23 million light-years.

This Hubble image of the heart of M51a at right shows its strong spiral character. 这张哈勃图像显示了M51a星系的核心，展现了其显著的螺旋特征。 The intriguing image below shows the heart of M51a as taken by the Wide Field and Planetary Camera of Hubble. The pattern is interpreted as bands of dust absorption and is taken to locate the position of a black hole at the center of the galaxy. 下面这张引人入胜的图像显示了M51a星系的核心，由哈勃太空望远镜的广域及行星照相机拍摄。这种图案被解释为尘埃吸收带，并被用来确定星系中心黑洞的位置。 whirlpool galaxy，M51a 和伴星 M51b（资料来源：NASA，ESA，S. Beckwith（STSci）和哈勃遗产团队（STSci/AURA），哈勃太空望远镜 ACS。）

Sources

• M51: The Whirlpool Galaxy in Dust and Stars
  M51：尘埃与恒星中的漩涡星系
• Out of This Whirl: the Whirlpool Galaxy (M51) and Companion Galaxy.
  从漩涡中来：漩涡星系（M51）及其伴星系。
• "X"-Structure at Core of Whirlpool Galaxy
  whirlpool galaxy 的核心结构