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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.

霍格天體:近乎完美的環(huán)狀星系

當(dāng)天文學(xué)家亞瑟·霍格在1950年偶然發(fā)現(xiàn)這個(gè)星系后，疑問(wèn)就接踵而來(lái)，這究竟是一個(gè)星系還是兩個(gè)？這個(gè)環(huán)狀星系（霍格天體）外側(cè)是一道由藍(lán)色的年輕恒星組成的環(huán)，而中心附近則是由一些古老、黯淡的恒星作為的內(nèi)核。內(nèi)核和外環(huán)之間的裂縫近乎完全黑暗。霍格天體是如何形成的？由恒星和氣體構(gòu)成的外層結(jié)構(gòu)是如何演變成近乎完美的環(huán)形？這依然是個(gè)謎。一種假說(shuō)認(rèn)為，數(shù)十億年前的星系碰撞和中心棒狀結(jié)構(gòu)的引力效應(yīng)形成了霍格天體，而中心的棒狀結(jié)構(gòu)現(xiàn)在卻已經(jīng)消失的無(wú)影無(wú)蹤。這張圖的原始影像由哈勃太空望遠(yuǎn)鏡拍攝，近期使用了新的去噪算法進(jìn)行了再處理。對(duì)無(wú)線電波的觀測(cè)表明，霍格天體在過(guò)去的十億年中并沒(méi)有吞噬一個(gè)更小的星系?；舾裉祗w跨度約10萬(wàn)光年，位于巨蛇座方向，距離地球約6億光年。在右側(cè)可以看到許多遙遠(yuǎn)的星系，而巧合的是在裂縫中的七點(diǎn)鐘方向還可以看到另一個(gè)更遙遠(yuǎn)的環(huán)狀星系。   

高清原圖地址：

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

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