神秘的環(huán)狀星系一直困擾著天文學(xué)家

神秘的環(huán)狀星系一直困擾著天文學(xué)家

Of all the galaxies observed by astronomers, barely any are as strange or geometrically unique as Hoag's Object. This bizarre galactic circle, categorized as a "ring galaxy," is located some 600 million light-years from Earth in the constellation Serpens and spans about 120,000 light-years across. Even more befuddling is that Hoag's Object is not one, but two galaxies — a cosmic arrangement that has baffled researchers since its discovery by American astronomer Arthur Hoag in 1950.

在天文學(xué)家觀測(cè)到的所有星系中，幾乎沒有一個(gè)像霍格星系那樣奇特或在幾何上獨(dú)一無(wú)二。這個(gè)奇異的星系圈被歸類為“環(huán)狀星系”，位于巨蛇星座，距地球約6億光年，跨度約12萬(wàn)光年。更令人困惑的是，霍格的目標(biāo)不是一個(gè)，而是兩個(gè)星系——自1950年美國(guó)天文學(xué)家阿瑟·霍格發(fā)現(xiàn)霍格星系以來(lái)，這種宇宙布局一直困擾著研究人員。

Hoag's Object, a rare ring galaxy located some 600 million light-years from Earth. (Photo: NASA and The Hubble Heritage Team (STScI/AURA); Acknowledgment: Ray A. Lucas (STScI/AURA) [public domain]/Wikimedia Commons)

At first, astronomers believed the unusual arrangement of Hoag's Object was a trick of the eye caused by gravitational lensing. This phenomenon, first proposed by Einstein's Theory of General Relativity, occurs when the gravitational mass of one object can bend light in such a way as to magnify the appearance of a more distant object. Astronomers have used such cosmic lenses before to peer into the distant hearts of other galaxies that would otherwise be impossible to detect with modern instruments. This idea was later disproved after observations of Hoag's Object in 1974 showed it weighed far too little (about the mass of 700 billion suns) to cause gravitational lensing of any magnitude.

起初，天文學(xué)家們認(rèn)為霍格的物體的不同尋常的排列是由引力透鏡效應(yīng)引起的。這一現(xiàn)象最初是由愛因斯坦的廣義相對(duì)論提出的，當(dāng)一個(gè)物體的引力質(zhì)量可以使光彎曲，從而放大遠(yuǎn)處物體的外觀時(shí)，就會(huì)出現(xiàn)這種現(xiàn)象。天文學(xué)家以前曾使用過這樣的宇宙透鏡來(lái)窺視其他星系遙遠(yuǎn)的中心，否則用現(xiàn)代儀器是無(wú)法探測(cè)到的。這個(gè)想法后來(lái)被證明是錯(cuò)誤的，因?yàn)?974年對(duì)霍格星的觀測(cè)表明它的質(zhì)量太小了(大約7000億個(gè)太陽(yáng)的質(zhì)量)，不足以產(chǎn)生任何量級(jí)的引力透鏡效應(yīng)。

Instead, Hoag's Objects features what appear to be two distinct galaxies, with young bright blue stars encircling a center core of older reddish-stars. Between them lies a perceptible moat of darkness.

相反，霍格星系的特征似乎是兩個(gè)截然不同的星系，年輕的亮藍(lán)色恒星環(huán)繞著較老的紅色恒星的中心核心。在他們之間有一條可以看見的黑暗的護(hù)城河。

"It's one of these weird little objects you point at without fully understanding what they mean," François Schweizer of the Carnegie Observatories in Pasadena, California, told New Scientist in 2011.

加州帕薩迪納卡耐基天文臺(tái)的弗朗索瓦·施韋澤在2011年接受《新科學(xué)家》采訪時(shí)表示:“這是一種奇怪的小東西，你指著它卻不完全明白它的意思。”

The Vela ring galaxy, visible as a bright core surrounded by a baby blue halo. (Photo: European Space Agency/CC 2.0)

So how did these incredibly rare cosmic anomalies, accounting for only .01% of all the galaxies discovered, ever come to be? The most popular theory presently is that Hoag's Object was once a common disc-shaped galaxy that suffered a direct hit from a smaller, neighboring galaxy. The resulting collision, which would have happened billions of years ago, wrapped the original galaxy's gravitational pull and formed the beautiful symmetry we see today.

那么，這些罕見得令人難以置信的宇宙異常是如何形成的呢?目前最流行的理論是，霍格的目標(biāo)曾經(jīng)是一個(gè)普通的圓盤狀星系，它直接受到了鄰近較小星系的撞擊。由此產(chǎn)生的碰撞可能發(fā)生在數(shù)十億年前，它包裹了原始星系的引力，形成了我們今天看到的美麗的對(duì)稱。

Another theory posits that the galaxy has simply sucked in enough intergalactic mass over time to form the beautiful ring we see today.

另一種理論認(rèn)為，隨著時(shí)間的推移，星系只是吸收了足夠的星系間質(zhì)量，形成了我們今天看到的美麗的環(huán)。

At the one o'clock position in this image, you can see yet another ring galaxy in the distance behind Hoag's Object. (Photo: NASA/Hubble Space Telescope)

Formation theories aside, astronomers noted something else incredible about Hoag's Object when they trained the Hubble Telescope's sensitive optics on it back in 2002. Hiding behind this cosmic wonder at the one o'clock position in the above photo is yet another rare ring galaxy –– making this an image of a galaxy within a galaxy within a galaxy within a galaxy!

撇開形成理論不談，2002年，天文學(xué)家們將哈勃望遠(yuǎn)鏡的靈敏光學(xué)儀器對(duì)準(zhǔn)霍格的天體時(shí)，還發(fā)現(xiàn)了其他一些不可思議的現(xiàn)象。上圖中1點(diǎn)鐘位置的宇宙奇觀背后，隱藏著另一個(gè)罕見的環(huán)狀星系——這是一張星系中的星系!