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已发现的奇怪星际天体可能是一颗死星的碎片

  '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.

  奥陌陌(Oumuamua)是已知的第一个来自太阳系之外的天体,它可能是一颗行星被一颗遥远的恒星撕裂时形成的长方形的天体。

  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,一位不寻常的访客出现在太阳系附近——这是一个比较小的岩石天体,它并非来自地球附近,而是诞生于一个非常遥远的恒星系统中。

  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.

  发现这位星际访客的团队给它起了个名字叫奥陌陌。“奥陌陌”在夏威夷语中意为“第一位来自远方的信使”。它给人们带来了许多困惑。位于夏威夷毛伊岛上哈雷阿卡拉天文台(haleakala observatory)的泛星计划(Pan-STARRS)望远镜首次对奥陌陌进行观测,观测显示奥陌陌以一种无法仅用重力来解释的方式加速。根据它反射的光线,奥陌陌的外形呈细长的雪茄状,它的形状与我们在太阳系看到的任何物体都不同。

  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.

  新的计算机模拟结果揭示了这个奇怪的星际天体可能的起源:一个行星被它的母星撕成碎片,留下一长串细细的碎片。其中的一些碎片可能已经飞到周围的星际空间,于是几百万甚至几十亿年后,奥陌陌到达了我们的太阳系。这些模拟结果指出了奥陌陌能的三种可归属类型,并解释了这位“星际访客”细长的形状和奇怪运动方式。

  “’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.”

  法国蔚蓝海岸天文台的研究员、今天在《自然·天文学》杂志上发表了关于奥陌陌的起源模拟研究的第一作者——张韵表示:“针对奥陌陌的出现,人们提出了很多问题来解释它的起源。但是之前的研究无法解释奥陌陌如此细长的形状。”

  A mystery from beyond

  来自远方的神秘天体


  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.

  天文学家一直怀疑有星际天体在我们的太阳系中穿行,它们被发现只是时间问题。但他们猜测这些物体看起来更像最近发现的星际彗星博里索夫(Borisov)。博里索夫是一个有着冰晕、正在分解的星体,它看起来就像太阳系外围的冰冻物体。

  “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.”

  耶鲁大学天文学教授格Greg Laughlin说:“有了博里索夫,我们就能准确地理解我们所研究的“星际访客”的行为举止。博里索夫的一切都很普通。而这与奥陌陌形成了惊人的对比,奥陌陌各方面都表现出了不同寻常之处。”

  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.

  奥陌陌不是冰冷的彗星,而是多岩石的,干燥的,更像是小行星。它太小太暗,无法直接观测到它的表面,所以天文学家根据它翻转时的反射光来推断它的形状。它那奇怪的细长形状立即引发了对其起源的猜测。当天文学家继续观测奥陌陌的运行轨迹时,他们发现了奇怪的加速现象,认为这是从它表面喷发的水蒸气导致的。

  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,奥陌陌的起源仍然是一个谜,但是,“所有这些难题都可以通过我们的方案来解决。”张韵说。

  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.

  张韵和她加州大学圣克鲁斯分校的同事Doug Lin考虑了以下可能性:奥陌陌来自一个有行星或更小的星子围绕一个密度大的小恒星运行的系统。恒星的引力足以摧毁那些靠得太近的星球,而不会把它们烧成碎片。

  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.

  该研究小组绘制了围绕这些恒星运行的三种天体的轨迹:半英里宽的星子,类似于彗星的冰冻星体以及诸如“超级地球”之类的较大行星。

  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.

  张韵和Doug Lin发现,如果这些天体中的任何一种处于其母恒星22万英里范围内时,它们就会被恒星的引力旋转、拉伸和撕碎,这一过程被天文学家们称之为“潮汐撕裂”。天体越小,被撕裂的距离就越近。根据母星世界的组成,被撕裂的碎片可能形成翻滚的、极其细长的星体,类似奥陌陌。由于这个过程爆发的巨大能量,许多碎片被喷射到星际空间,永远不会回来。

  “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说,“大自然并不会制造出很多碎片一样的物体。而潮汐撕裂确实会促成这类星体的形成。这是一个非常值得探索的想法,他们已经做了非常完整和仔细的工作去探索这一想法。”

  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.

  模拟过程还表明,当母星被撕裂时,恒星的热量会融化被撕裂的碎片,蒸发碎片表面的水。但是深埋在这些碎片里的冰仍然存在,这可以解释当奥陌陌靠近太阳系时,由于它喷射的水蒸气推动产生加速度的假设。

  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.

  当这些行星碎片融化并重新分解时,这些岩石会变得更坚硬,形成坚硬的外壳,就像融化后冷却的巧克力一样。张韵说,“在星体表面重塑后,再使其分裂就更难了。”这种回火过程可以解释为什么奥陌陌在经过我们的太阳时没有完全崩溃,而博里索夫,它最近在离开太阳系的途中分裂了。

  Cigar shape,or pancake?

  雪茄形状或煎饼形状?


  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.

  新西兰坎特伯雷大学的米歇尔·班尼斯特(Michele Bannister)也在研究星际天体,她表示,这些模拟很好地解释了像奥陌陌这样的天体是如何形成的。“我认为他们正在研究的一些机制比其他的机制更有说服力。”班尼斯特指出,假设彗星是奥陌陌的母体,是最有意义的,而假设超级地球大小的行星是它的母星则不那么有说服力。

  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都给这个谜团带来了新的线索:针对去年夏天发表的重新审视了对奥陌陌的原始观测结果的论文,他们怀疑奥陌陌实际上是一个雪茄形状的星体。最新的分析认为,奥陌陌可能有一个类似煎饼的形状。班尼斯特把这种形状比作一个鼓鼓囊囊的圆面饼,类似于太阳系外的MU69星体或Arrokoth星体。

  “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.”

  班尼斯特说:“‘新视野号’飞过Arrokoth星体时,我们发现了什么?我们发现两个厚皮塔面包粘在一起。这很有趣,也很有启发性。”

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

  如果奥陌陌不是潮汐撕裂中喷射出来的岩石碎片,那么它的真正起源仍然扑朔迷离。

  “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说,“如果你假设这个奥陌陌是雪茄形状的,这是一个非常合理的端对端的描述。但如果假设奥陌陌是一个煎饼形状的星体,那么整个探索又回到了原点。”
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