2019 August 11

Arp 87: Merging Galaxies from Hubble
Image Credit:
NASA, ESA, Hubble Heritage Team (STScI, AURA)

Explanation: This dance is to the death. Along the way, as these two large galaxies duel, a cosmic bridge of stars, gas, and dust currently stretches over 75,000 light-years and joins them. The bridge itself is strong evidence that these two immense star systems have passed close to each other and experienced violent tides induced by mutual gravity. As further evidence, the face-on spiral galaxy on the right, also known as NGC 3808A, exhibits many young blue star clusters produced in a burst of star formation. The twisted edge-on spiral on the left (NGC 3808B) seems to be wrapped in the material bridging the galaxies and surrounded by a curious polar ring. Together, the system is known as Arp 87 and morphologically classified, technically, as peculiar. While such interactions are drawn out over billions of years, repeated close passages should ultimately result in the death of one galaxy in the sense that only one galaxy will eventually result. Although this scenario does look peculiar, galactic mergers are thought to be common, with Arp 87 representing a stage in this inevitable process. The Arp 87 pair are about 300 million light-years distant toward the constellation Leo. The prominent edge-on spiral galaxy at the far left appears to be a more distant background galaxy and not involved in the on-going merger.

Arp 87: 哈伯望远镜拍摄的合并星系
NASA, ESA, Hubble Heritage Team (STScI, AURA)

说明: 这是死亡之舞。在此过程中,随着这二个大星系进行缠斗,一道由恒星、云气和尘埃所构成,绵延超过75,000光年的宇宙桥,联结了这对星系。这道长桥明确指证,这两个庞大的恒星系统曾近距离通过对方附近,彼此间的重力引发了强烈的潮汐。作为进一度的佐证,影像右侧的正向螺旋星系NGC 3808A,触发了爆发性的恒星形成活动,并产生许多泛蓝年轻星团。而左方扭曲的侧向星系NGC 3808B,则包裹在连接星系的长桥物质里,并拥有一个有趣的绕极环。这个合称为Arp 87的系统,因其外貌而被归类为特殊天体。这种重力互扰的历程长达数十亿年,但反覆的近距离通过,终究会造成其中一个星系死亡,因为最后它们会合并成单一星系。虽然这幅景象看起来相当奇特,但星系合并咸认是很常见的现象,而Arp 87 是这种 必然过程的中间阶段。 Arp 87星系对位在狮子座方向,离我们约3亿光年远。影像左缘的清晰侧向螺旋星系,是一个更遥远的背景星系,并未参与这场进行中的星系合并。

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