Copyright:Denis Priou
原文:
Galactic or open star clusters are young. These swarms of stars are born together near the plane of the Milky Way, but their numbers steadily dwindle as cluster members are ejected by galactic tides and gravitational interactions. In fact, this bright open cluster, known as M46, is around 300 million years young. It still contains a few hundred stars within a span of 30 light-years or so. Located about 5,000 light-years away toward the constellation Puppis, M46 also seems to contain contradictions to its youthful status. In this pretty starscape, the colorful, circular patch above and right of the center of M46 is the planetary nebula NGC 2438. Fainter still, a second planetary nebula, PK231+4.1, is identified by the box at the right and enlarged in the inset. Planetary nebulae are a brief, final phase in the life of a sun-like star a billion years old or more, whose central reservoir of hydrogen fuel has been exhausted. NGC 2438 is estimated to be only 3,000 light-years distant, though, and moves at a different speed than M46 cluster members. Along with its fainter cohort, planetary nebula NGC 2438 is likely only by chance appearing near our line-of-sight to the young stars of M46.
中文翻譯:
以下是你要的內容，會保持專有名詞的英文名稱並使用香港的繁體字：
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#M46 #NGC2438 #天文學 #行星狀星雲 #開放星團 #星系探索
年輕的星團——如银河系中的開放星團，通常在靠近銀河平面的位置誕生。然而，隨著時間推移，這些星團中的成員因為銀河潮汐和重力互動而逐漸減少。這個明亮的開放星團M46大約有3億年歷史，內裡仍然有幾百顆星星，範圍大約為30光年。
M46位於距離我們約5,000光年的Puppis星座中，然而它的年輕狀態似乎存在矛盾。在這幅美麗的星空畫面中，位於M46中心上方及右方的五光十色圓形區域是行星狀星雲NGC 2438。更微弱的行星狀星雲PK231+4.1則在右側框內標識，並在插圖中放大顯示。
行星狀星雲是類似太陽的恆星在耗盡其中央氫燃料後進入的短暫最後階段，通常它們的年齡達到10億年以上。值得注意的是，NGC 2438的估計距離約為3,000光年，並且其移動速度和M46星團的成員不同，因此，NGC 2438及其較微弱的同伴有可能只是巧合出現在我們與年輕的M46星星之間的視線上。
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來源:NASA每日圖片
