This Galaxy Doesn't Have Dark Matter, and That's Weird
This picture shows NGC1052 (on left), a massive elliptical galaxy that dominates the neighborhood where NGC1052-DF2 also lives. NGC1052-DF2 is an ultra-diffuse galaxy located 65 million light-years away that seems to be missing itsdark matter. Also pictured are NGC1042 (the main spiral) and NGC1048 (the two interacting galaxies on the bottomright).?
這個星系不含暗物質(zhì)瞳氓，這很奇怪呀（that's weird）
左圖是NGC1052六剥，一個巨大橢圓形星系，主宰著她的鄰居NGC1052-DF2 。NGC1052-DF2 是一個超彌散星系，距離NGC1052有6.5億光年那么遠(yuǎn)以至于在圖片中看起來就像沒有暗物質(zhì)一樣。圖中還有NGC1042（中間的漩渦）以及NGC1048（在右下角兩個相互影響的星系）。
Dark matter is the bedrock that all galaxies are anchored to. You can't get one without the other. Or so we thoughtuntil astronomers found a ghostly galaxy that doesn't appear to contain any dark matter. It's as if the universe isplaying a trick on us by flipping the laws of physics on their head — dark matter should be there, but it isn't.?
暗物質(zhì)是所有星系固定（be anchored to）的河床，你不能顧此失彼攘已。我們一直這樣認(rèn)為，一直到天文學(xué)家發(fā)現(xiàn)了一個幽靈般的星系怜跑，這個星系看起來沒有任何暗物質(zhì)贯被。這就像宇宙對我們開了一個玩笑，他們翻轉(zhuǎn)了物理定律（flip ...on their head）這些暗物質(zhì)本應(yīng)在那里妆艘，然而他們并不在彤灶。
It's a "game changer" galaxy, astronomers are saying, and it's like nothing we've ever seen before.
天文學(xué)家說這是一個“改變游戲規(guī)則”的星系，我們此前從未見過類似情況（it's like nothing we've ever seen before.? ）批旺。
We may not be able to spot dark matter, but astronomers can measure its gravitational effects acting on normalmatter. For example, they can look at how fast stars cruise around a galaxy. When dark matter is present, thatgalaxy's gravity will be bulked up, causing its stars to move faster than if just normal matter were present.?
我們也許看不到暗物質(zhì)幌陕，但天文學(xué)家可以測量他對普通物質(zhì)的引力。比如汽煮，他們可以觀察星系周圍星球漫游的速度搏熄。當(dāng)暗物質(zhì)存在時，星系的重力會增加暇赤，這會讓他周圍的星球移動速度比那些周圍只有普通物質(zhì)存在的星球快心例。
But in the case of NGC1052-DF2, an ultra-diffuse galaxy located 65 million light-years away, astronomers have foundthat its stars are moving in exactly the way that would be predicted if only the total mass of all the visible stuff isconsidered. In other words, dark matter doesn't seem to be exerting its gravity on normal matter in that galaxy. Andthat's weird.?
但是，就NGC1052-DF2這個距離地球6.5億光年的超漫射星球來說鞋囊，天文學(xué)家發(fā)現(xiàn)只要能觀測到周圍所有觀測到的物質(zhì)總量止后，它周圍星球運行的路徑就可以預(yù)測。也就是，在這個星系暗物質(zhì)好像對其他物體沒有引力作用译株。這真的很奇怪瓜喇。
"Finding a galaxy without dark matter is unexpected because this invisible, mysterious substance is the mostdominant aspect of any galaxy," Pieter van Dokkum, of Yale University, said in a statement. "For decades, we thoughtthat galaxies start their lives as blobs of dark matter. After that everything else happens: gas falls into the dark matterhalos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. NGC1052-DF2challenges the standard ideas of how we think galaxies form."?
耶魯大學(xué)的Pieter van Dokkum說在一次陳述中說，發(fā)現(xiàn)一個沒有暗物質(zhì)的星系出乎我們的意料歉糜，因為這種無形且神秘的物質(zhì)是主宰星系的主要力量乘寒。幾十年來，我們一直認(rèn)為星系是以一小點暗物質(zhì)為基礎(chǔ)孕育匪补，然后有氣體落入暗物質(zhì)的外暈伞辛，然后變成星球，再慢慢長大夯缺，在這樣一系列過程發(fā)生后形成現(xiàn)在的星系蚤氏。但是NGC1052-DF2的發(fā)現(xiàn)打破了我們對星系形成的固有觀念。
Ultra-diffuse galaxies are oddities in their own right, having only been discovered in 2015 as they are very difficult todetect. However, it appears that this class of galaxy is common, but none are like NGC1052-DF2.?
超彌散星系本身(in their own right）就很奇怪喳逛，因其很難被觀測到直到2015年才被發(fā)現(xiàn)，但這組星系很尋常棵里，并不像NGC1052-DF2.?
The galaxy was discovered using the Dragonfly Telephoto Array, a telescope in New Mexico that's custom-made toseek out these elusive targets. Then, using the twin 10-meter optical and infrared telescopes at the W. M. KeckObservatory on Mauna Kea in Hawaii, the astronomers singled out 10 bright globular clusters (large compact groupsof stars orbiting the galaxy's core) and used spectral data to measure their motions. These clusters were found to beplodding along more slowly than expected, meaning there's far less mass in that galaxy than would be predicted. Infact, there's so little mass that the researchers have come to the astonishing conclusion that there's little, if any, darkmatter there.?
這個星系是由Dragonfly這個天文相片矩陣發(fā)現(xiàn)的润文，這個位于新墨西哥的特制望遠(yuǎn)鏡是用來尋找難發(fā)現(xiàn)的目標(biāo)。在夏威夷州莫奈克亞山上殿怜，宇航員用雙倍十米口徑光學(xué)和紅外望遠(yuǎn)鏡篩選出（single? out）10個球狀聚集物（巨大的典蝌，緊密成團的眾多星球環(huán)繞著星系中心運行）并用波譜數(shù)據(jù)測算出他們的運行。結(jié)果發(fā)現(xiàn)這些星球運行的速度比預(yù)期的要慢很多头谜。實際上骏掀，這里的物質(zhì)太少了，所以研究者得出驚人結(jié)論柱告，這里即使有暗物質(zhì)也極少截驮。
Follow-up observations were made by the Gemini North telescope, also on Mauna Kea, so the galaxy's structure couldbe studied. With Gemini's help, the researchers ruled out interactions with other galaxies as being the cause of itsweird dark matter deficit.?
后續(xù)的觀察也是在莫奈克亞山上，用雙子北座望遠(yuǎn)鏡觀測使得可以繼續(xù)研究星系的結(jié)構(gòu)际度。通過雙子座望遠(yuǎn)鏡葵袭，研究者可以排除其他星系的干擾，這些干擾是由奇怪的其暗物質(zhì)不足導(dǎo)致的乖菱。
"If there is any dark matter at all, it's very little," said van Dokkum in the press release. "The stars in the galaxy canaccount for all of the mass, and there doesn't seem to be any room for dark matter."?
van Dokkum在新聞稿（press release）中說坡锡，這個星系中即使有暗物質(zhì)，也很少窒所。在這個星系中的星球幾乎是它所有的物質(zhì)了鹉勒，沒有暗物質(zhì)的空間了。
This finding seems to suggest that dark matter has "its own separate existence apart from other components ofgalaxies," he added. And this makes the very existence of NGC1052-DF2 a mystery. If it has no dark matter, how did iteven evolve into a galaxy??
他補充說吵取，這個發(fā)現(xiàn)似乎暗示著暗物質(zhì)有自己獨特的存在方式禽额，這種存在方式有別于眾多星系中的其他物質(zhì)。這使得NGC1052-DF2成為一個特別且神秘的存在皮官。如果沒有暗物質(zhì)的話绵疲，那它是怎么演變成一個星系的呢哲鸳？
In their study published in the March 29 issue of Nature, van Dokkum's team speculates that some cataclysmic eventin the galaxy may have cleared out all the dark matter and blasted away all the star-forming gases. Alternatively, thenearby massive elliptical galaxy NGC 1052 may have played a role in NGC1052-DF2's lack of dark matter billions ofyears ago when it was undergoing the early and violent stages of evolution.?
? 5月29日發(fā)表在《自然》雜志上的研究, van Dokkum's的團隊推測，在星系中發(fā)生了一些演變事件清除了所有暗物質(zhì)并噴射出所有星狀氣體盔憨。也許在幾十億年前當(dāng)它正在經(jīng)歷早期巨大演變階段時徙菠，它附近的橢圓星系NGC 1052對于NGC1052-DF2缺乏暗物質(zhì)也起到了重要作用。
Now, the researchers are poring over Hubble Space Telescope observations of similar galaxies to perhaps find morethat lack dark matter. If they find more, then ultra-diffuse and faint galaxies might be the norm if dark matter isn'tpresent. And that's a fascinating development in our understanding of how galaxies evolve.?
如今郁岩，研究人員正在用哈勃望遠(yuǎn)鏡仔細(xì)觀察尋找那些也許也缺少暗物質(zhì)的更小的星系婿奔。 如果可以找到更多，那么超彌散星系和微弱（faint）星系不存在暗物質(zhì)可能就是標(biāo)準(zhǔn)了问慎。那對我們在理解星系演變過程貢獻(xiàn)將是巨大的萍摊。
"Every galaxy we knew about before has dark matter, and they all fall in familiar categories like spiral or ellipticalgalaxies," concluded van Dokkum. "But what would you get if there were no dark matter at all? Maybe this is whatyou would get."?
van Dokkum說以前我們知道的所有含有暗物質(zhì)的星系，他們都會被歸類到熟知的橢圓星系或漩渦星系如叼。但是如果根本沒有暗物質(zhì)要怎樣歸類冰木？也許這就是接下來需要研究的。
