Astronomy Picture of the Day——霍格天体:近乎完美的环状星系

Hoag's Object: A Nearly Perfect Ring Galaxy 
Image Credit: NASA, ESA, Hubble; Processing: Benoit Blanco

Explanation: Is this one galaxy or two? This question came to light in 1950 when astronomer Arthur Hoag chanced upon this unusual extragalactic object. On the outside is a ringdominated by bright blue stars, while near the center lies a ball of much redder stars that are likely much older. Between the two is a gap that appears almost completely dark. How Hoag's Object formed, including its nearly perfectly round ring of stars and gas, remains unknown. Genesis hypotheses include a galaxy collision billions of years ago and the gravitational effect of a central bar that has since vanished. The featured photo was taken by the Hubble Space Telescope and recently reprocessed using an artificially intelligent de-noising algorithm. Observations in radio waves indicate that Hoag's Object has not accreted a smaller galaxy in the past billion years. Hoag's Object spans about 100,000 light yearsand lies about 600 million light years away toward the constellation of the Snake (Serpens). Many galaxies far in the distance are visible toward the right, while coincidentally, visible in the gap at about seven o'clock, is another but more distant ring galaxy.

霍格天体:近乎完美的环状星系

当天文学家亚瑟·霍格在1950年偶然发现这个星系后，疑问就接踵而来，这究竟是一个星系还是两个？这个环状星系（霍格天体）外侧是一道由蓝色的年轻恒星组成的环，而中心附近则是由一些古老、黯淡的恒星作为的内核。内核和外环之间的裂缝近乎完全黑暗。霍格天体是如何形成的？由恒星和气体构成的外层结构是如何演变成近乎完美的环形？这依然是个谜。一种假说认为，数十亿年前的星系碰撞和中心棒状结构的引力效应形成了霍格天体，而中心的棒状结构现在却已经消失的无影无踪。这张图的原始影像由哈勃太空望远镜拍摄，近期使用了新的去噪算法进行了再处理。对无线电波的观测表明，霍格天体在过去的十亿年中并没有吞噬一个更小的星系。霍格天体跨度约10万光年，位于巨蛇座方向，距离地球约6亿光年。在右侧可以看到许多遥远的星系，而巧合的是在裂缝中的七点钟方向还可以看到另一个更遥远的环状星系。

高清原图地址：

https://apod.nasa.gov/apod/image/1911/Hoag_HubbleBlanco_3000.jpg

近期文章：

Astronomy Picture of the Day——木卫二的重制影像

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