Copyright:R Jay Gabany
原文:
NGC 4631 is a spiral galaxy found only 25 million light-years away, toward the well-trained northern constellation Canes Venatici. Seen egde-on, the galaxy is similar in size to the Milky Way. Its distorted wedge shape suggests to some a cosmic herring and to others its popular moniker, The Whale Galaxy. The large galaxy’s small, remarkably bright elliptical companion NGC 4627 lies just above its dusty yellowish core, but also identifiable are recently discovered, faint dwarf galaxies within the halo of NGC 4631. In fact, the faint extended features below (and above) NGC 4631 are now recognized as tidal star streams. The star streams are remnants of a dwarf satellite galaxy disrupted by repeated encounters with the Whale that began about 3.5 billion years ago. Even in nearby galaxies, the presence of tidal star streams is predicted by cosmological models of galaxy formation, including the formation of our own Milky Way.
中文翻譯:
🌌 NGC 4631，亦即「鯨魚星系」 (The Whale Galaxy)，距離地球約2500萬光年，位於北方星座「獵犬座」 (Canes Venatici)。這個星系呈邊緣狀顯現，與我們的銀河系 (Milky Way) 大小相似。其獨特的扭曲刀片形狀讓一些人聯想到宇宙中的鯧魚。
在這個巨大的星系中，我們可以看到其小而明亮的橢圓形伴星 NGC 4627，恰好位於其淡黃色核心之上。最近發現的、散淡的矮星系亦在 NGC 4631 的光環中可見。事實上，NGC 4631 上下的散開特徵被認識為潮汐恆星流 (tidal star streams)。這些恆星流是由於一個矮衛星星系因與鯨魚星系的多次近距離接觸而被打斷所留下的痕跡，這一過程約在 35 億年前開始。
即便在附近的星系中，潮汐恆星流的存在也被宇宙學的星系形成模型預測到，這包括我們自己的銀河系的形成。
#NGC4631 #WhaleGalaxy #CanesVenatici #CosmicHerring #TidalStreams #GalaxyFormation #Astronomy #Space #DwarfGalaxies #MilkyWay
來源:NASA每日圖片
