已發現的奇怪星際天體可能是一顆死星的碎片

　　'Oumuamua,the first object known to have come from beyond the solar system,might have gotten its oblong shape when a planet was shredded by a faraway star.

　　奧陌陌（Oumuamua）是已知的第一個來自太陽系之外的天體，它可能是一顆行星被一顆遙遠的恒星撕裂時形成的長方形的天體。

　　An unusual visitor cruised through the solar system in late 2017—a small,rocky object that did not hail from Earth’s neighborhood,but was born in a star system far,far away.

　　2017年年底，一位不尋常的訪客出現在太陽系附近——這是一個比較小的巖石天體，它并非來自地球附近，而是誕生于一個非常遙遠的恒星系統中。

　　The interstellar visitor—named‘Oumuamua by the team that discovered it,which roughly translates from Hawaiian as“a messenger from afar arriving first”—provided more than a few puzzles.First spotted by the Pan-STARRS project at the HaleakalāObservatory in Maui,the tumbling object accelerated in ways that could not be explained by gravity alone.And based on the light it reflected,‘Oumuamua appeared to be an elongated,cigar-shaped object—a shape unlike anything seen in our own solar system.

　　發現這位星際訪客的團隊給它起了個名字叫奧陌陌。“奧陌陌”在夏威夷語中意為“第一位來自遠方的信使”。它給人們帶來了許多困惑。位于夏威夷毛伊島上哈雷阿卡拉天文臺（haleakala observatory）的泛星計劃（Pan-STARRS）望遠鏡首次對奧陌陌進行觀測，觀測顯示奧陌陌以一種無法僅用重力來解釋的方式加速。根據它反射的光線，奧陌陌的外形呈細長的雪茄狀，它的形狀與我們在太陽系看到的任何物體都不同。

　　New computer simulations reveal a possible origin story for this strange interstellar object:A world was ripped to pieces by its home star,leaving behind a wake of long,thin fragments.Some of these fragments would have been launched into interstellar space,and millions—perhaps billions—of years later,‘Oumuamua reached our solar system.The simulations point to three possible types of home systems for‘Oumuamua,and the work explains both the elongated shape and curious motion of the interstellar visitor.

　　新的計算機模擬結果揭示了這個奇怪的星際天體可能的起源：一個行星被它的母星撕成碎片，留下一長串細細的碎片。其中的一些碎片可能已經飛到周圍的星際空間，于是幾百萬甚至幾十億年后，奧陌陌到達了我們的太陽系。這些模擬結果指出了奧陌陌能的三種可歸屬類型，并解釋了這位“星際訪客”細長的形狀和奇怪運動方式。

　　“’Oumuamua provides a lot of problems to explain its origin,”says Yun Zhang,a researcher at the C?te d’Azur Observatory in France and lead author of a study on the simulations published today in Nature Astronomy.“Before our study,no solution can produce such an elongated shape.”

　　法國蔚藍海岸天文臺的研究員、今天在《自然·天文學》雜志上發表了關于奧陌陌的起源模擬研究的第一作者——張韻表示：“針對奧陌陌的出現，人們提出了很多問題來解釋它的起源。但是之前的研究無法解釋奧陌陌如此細長的形狀。”

　　A mystery from beyond

　　來自遠方的神秘天體

　　Astronomers have always suspected that interstellar objects were traipsing through our solar system—it was just a matter of time until we spotted one.But they guessed those objects would look more like the recently discovered interstellar comet Borisov.A disintegrating world with an icy halo,Borisov looks like the frozen objects of the outer solar system.

　　天文學家一直懷疑有星際天體在我們的太陽系中穿行，它們被發現只是時間問題。但他們猜測這些物體看起來更像最近發現的星際彗星博里索夫（Borisov）。博里索夫是一個有著冰暈、正在分解的星體，它看起來就像太陽系外圍的冰凍物體。

　　“With Borisov,we get exactly what we expect an interstellar visitor would act like and do.Everything about it is completely ordinary,”says Greg Laughlin,a professor of astronomy at Yale University.“And that’s a startling contrast with‘Oumuamua,where literally nothing about‘Oumuamua was ordinary.”<紐約時報中英文網 http://www.244129.buzz/>

　　耶魯大學天文學教授格Greg Laughlin說：“有了博里索夫，我們就能準確地理解我們所研究的“星際訪客”的行為舉止。博里索夫的一切都很普通。而這與奧陌陌形成了驚人的對比，奧陌陌各方面都表現出了不同尋常之處。”

　　Instead of icy and comet-like,‘Oumuamua was rocky and dry,more like an asteroid.It was too tiny and dim to observe the surface directly,so astronomers inferred its shape based on how it reflected light as it tumbled.Its strange,elongated form immediately provoked speculation about its origins,and as astronomers continued to observe‘Oumuamua’s passage,they noticed curious accelerations that were ascribed to water vapor erupting from beneath its surface.

　　奧陌陌不是冰冷的彗星，而是多巖石的，干燥的，更像是小行星。它太小太暗，無法直接觀測到它的表面，所以天文學家根據它翻轉時的反射光來推斷它的形狀。它那奇怪的細長形狀立即引發了對其起源的猜測。當天文學家繼續觀測奧陌陌的運行軌跡時，他們發現了奇怪的加速現象，認為這是從它表面噴發的水蒸氣導致的。

　　As late as last year,‘Oumuamua’s origin was still a mystery,but,“all these puzzles can be solved by our scenario,”Zhang says.

　　直到去年，奧陌陌的起源仍然是一個謎，但是，“所有這些難題都可以通過我們的方案來解決。”張韻說。

　　How to make a space cigar

　　如何制作“太空雪茄”

　　Zhang and her colleague Doug Lin of the University of California,Santa Cruz,considered the possibility that‘Oumuamua came from a system with planets or smaller planetesimals orbiting a small,dense,central star—something with enough gravity to destroy worlds that come too close without burning them to a crisp first.

　　張韻和她加州大學圣克魯斯分校的同事Doug Lin考慮了以下可能性：奧陌陌來自一個有行星或更小的星子圍繞一個密度大的小恒星運行的系統。恒星的引力足以摧毀那些靠得太近的星球，而不會把它們燒成碎片。

　　The team plotted the trajectories of three types of objects orbiting these stars:half-mile-wide planetesimals,frozen objects similar to comets,and larger planets such as super-Earths.

　　該研究小組繪制了圍繞這些恒星運行的三種天體的軌跡：半英里寬的星子，類似于彗星的冰凍星體以及諸如“超級地球”之類的較大行星。

　　Zhang and Lin found that if any of these objects come within about 220,000 miles of their host star,they will be spun up,stretched out,and shredded by the star’s gravity—a process that astronomers call tidal disruption.The smaller the object,the closer it has to get to be ripped apart.Depending on the composition of the parent world,some of the fragments could be tumbling,extremely elongated objects like‘Oumuamua.And due to the violence of this process,many of the shards would launch into interstellar space,never to return.

　　張韻和Doug Lin發現，如果這些天體中的任何一種處于其母恒星22萬英里范圍內時，它們就會被恒星的引力旋轉、拉伸和撕碎，這一過程被天文學家們稱之為“潮汐撕裂”。天體越小，被撕裂的距離就越近。根據母星世界的組成，被撕裂的碎片可能形成翻滾的、極其細長的星體，類似奧陌陌。由于這個過程爆發的巨大能量，許多碎片被噴射到星際空間，永遠不會回來。

　　“Nature doesn’t make a lot of shard-like objects,”Laughlin says.“So the fact that tidal disruption does naturally do that makes it a very compelling idea to explore,and they’ve done a very complete and careful job of exploring that option.”

　　Laughlin說，“大自然并不會制造出很多碎片一樣的物體。而潮汐撕裂確實會促成這類星體的形成。這是一個非常值得探索的想法，他們已經做了非常完整和仔細的工作去探索這一想法。”

　　The simulations also suggest that when the parent worlds are ripped apart,the star’s warmth melts the fragments and vaporizes any water near the surface.But pockets of ice buried deep inside the fragments survive,which could explain the hypothesized jets of water vapor that pushed‘Oumuamua when it neared our sun.

　　模擬過程還表明，當母星被撕裂時，恒星的熱量會融化被撕裂的碎片，蒸發碎片表面的水。但是深埋在這些碎片里的冰仍然存在，這可以解釋當奧陌陌靠近太陽系時，由于它噴射的水蒸氣推動產生加速度的假設。

　　When these planetary fragments melt and resolidify,the rock becomes stronger and forms a tough outer crust,like melted and cooled chocolate.“It’s harder to take apart again after the surface freezes,”Zhang says.This tempering process could explain why‘Oumuamua didn’t crumble completely when it passed our sun,unlike Borisov,which recently broke apart on its way out of the solar system.

　　當這些行星碎片融化并重新分解時，這些巖石會變得更堅硬，形成堅硬的外殼，就像融化后冷卻的巧克力一樣。張韻說，“在星體表面重塑后，再使其分裂就更難了。”這種回火過程可以解釋為什么奧陌陌在經過我們的太陽時沒有完全崩潰，而博里索夫，它最近在離開太陽系的途中分裂了。

　　Cigar shape,or pancake?

　　雪茄形狀或煎餅形狀？

　　The simulations do a great job of explaining how objects like‘Oumuamua may form,says Michele Bannister of New Zealand’s University of Canterbury,who also studies interstellar objects.“I think some of the mechanisms they’re looking at are more likely than others,”she says,noting that a comet makes the most sense as a parent body for‘Oumuamua,while a super-Earth-sized planet isn’t as convincing.

　　新西蘭坎特伯雷大學的米歇爾·班尼斯特（Michele Bannister）也在研究星際天體，她表示，這些模擬很好地解釋了像奧陌陌這樣的天體是如何形成的。“我認為他們正在研究的一些機制比其他的機制更有說服力。”班尼斯特指出，假設彗星是奧陌陌的母體，是最有意義的，而假設超級地球大小的行星是它的母星則不那么有說服力。

　　But both she and Laughlin introduce a new wrinkle to the mystery:They’re skeptical that‘Oumuamua is actually a cigar-shaped object,pointing to a paper published last summer that revisited the original observations of the object.The newer analysis concludes that‘Oumuamua may actually have a pancake-like shape—a shape that Bannister likens to an overstuffed pita,similar to an object in the outer solar system called MU69,or Arrokoth.

　　但她和Laughlin都給這個謎團帶來了新的線索：針對去年夏天發表的重新審視了對奧陌陌的原始觀測結果的論文，他們懷疑奧陌陌實際上是一個雪茄形狀的星體。最新的分析認為，奧陌陌可能有一個類似煎餅的形狀。班尼斯特把這種形狀比作一個鼓鼓囊囊的圓面餅，類似于太陽系外的MU69星體或Arrokoth星體。

　　“We flew[the spacecraft]New Horizons past Arrokoth and what do we find?We find two overstuffed pita breads stuck together,”Bannister says.“It’s interesting and suggestive.”

　　班尼斯特說：“‘新視野號’飛過Arrokoth星體時，我們發現了什么？我們發現兩個厚皮塔面包粘在一起。這很有趣，也很有啟發性。”

　　If‘Oumuamua is not a stretched-out,rocky fragment,then its true origin remains shrouded.

　　如果奧陌陌不是潮汐撕裂中噴射出來的巖石碎片，那么它的真正起源仍然撲朔迷離。

　　“If you assume that the object was cigar-shaped,this is a very plausible end-to-end description of what it was,”Laughlin says.“But if it is the case that‘Oumuamua is a pancake-shaped thing,then that puts the whole thing back into the pure mystery zone.”

　　Laughlin說，“如果你假設這個奧陌陌是雪茄形狀的，這是一個非常合理的端對端的描述。但如果假設奧陌陌是一個煎餅形狀的星體，那么整個探索又回到了原點。”