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暗物质的秘密存在于太阳之中(图)

暗物质的秘密存在于太阳之中(图) 

这张X射线图像显示了太阳外围的大气——日冕,是由“日出”号X射线望远镜拍下的。

Sun Might Hold Secret of Dark Matter

 The identity of the mysterious dark matter thought to pervade the universe has eluded astrophysicists for decades. Now, for the first time a team hopes to look inside the sun for one of the prime candidates.  神秘的暗物质被认为充斥着整个宇宙,这个特性使其逃避天体物理学家们的追踪达数十年之久。目前,一个研究小组希望能够从太阳内部找到暗物质的主要候选粒子之一。
 The invisible stuff called dark matter is thought to make up as much as 90 percent of the universe's matter. To date, astrophysicists have only inferred the existence of some mysterious substance by identifying its gravitational effects on visible matter such as stars and galaxies. (For instance, dark matter makes galaxies spin faster than otherwise expected.) 科学家们认为,被称为暗物质的这种不可见物质在宇宙物质中所占份额高达90%。迄今为止,天体物理学家们已经推断出某种神秘物质的存在,但仅仅是通过它对可见物质(如:恒星和星系)的引力作用而推断出来的。例如,暗物质会使星系旋转得更快,否则星系就不可能旋转得如此之快。
 Two hypothetical particles have become the prime suspects to explain the fundamental make-up of dark matter: so-called axions and WIMPs (Weakly Interacting Massive Particles). Tens of teams are on the hunt for the heavyweight WIMPs, such as the GLAST team, which hopes to detect the gamma rays produced when, hypothetically, WIMPs and their antimatter selves annihilate each other.  为了解释暗物质的基本构成,两种假设的粒子成为主要的可疑对象,它们是所谓的轴子和弱作用重粒子WIMPs)。有几十个研究小组正在搜寻重量级的弱作用重粒子,如伽玛广域太空望远镜GLAST研究小组就是其中之一,该小组希望探测到伽马射线。但从假设的角度来讲,当弱作用重粒子以及它们自身的反物质之间相互作用而湮灭时,才会产生伽马射线。
 Only a handful of groups are searching for the lightweight particles called axions. For both sociological and technical reasons, WIMP searches far outnumber axion ones, according to David Tanner, a physicist at the University of Florida, and others. For instance, he said, detectors for WIMPs build more on the expertise of many astrophysicists. In addition, these massive particles are more fantastical.  只有少数研究小组正在搜寻叫做轴子的轻量级粒子。根据佛罗里达大学的物理学家大卫·坦纳及其他一些专家的说法,对弱作用重粒子的搜寻活动远远多于对轴子的搜寻,其中既有社会上的原因,也有技术上的原因。况且,这些重型粒子更具凭空想象的色彩。
 "WIMPs also imply things about supersymmetry and extra dimensions," Tanner told SPACE.com. "And so if they were detected, they would give theorists lots of new toys to play with, and new ideas to follow." “弱作用重粒子还意味着事物具有超对称性和额外维空间,”坦纳告诉太空网的记者说,“因此,如果探测出这种粒子,理论家们就会开发出许多好玩的新玩具,提出许多值得遵从的新观点。”
 A team led by X-ray astronomer Hugh Hudson of UC Berkeley says, however, that they are onto a promising and new way to search for the axion: Looking inside the sun. 然而,加州大学伯克利分校的X射线天文学家休·赫德森领导的一个研究小组称,他们正在利用一个富有希望的新方法来搜寻轴子:从太阳内部来寻找。
 Hudson presented his research at a recent meeting of the American Astronomical Society (AAS) in St. Louis. 赫德森把他的研究成果提交到美国天文协会最近在圣路易斯举行的一次会议上。
 Solar axions 太阳轴子
 The axion is extremely lightweight with neither electric charge nor spin, so it hardly interacts with the universe's surrounding matter — that's if the particle even exists. 轴子是极其轻微的粒子,既没有电荷也不旋转,因此它几乎不与宇宙间任何周围的物质发生相互作用——当然是说如果这种粒子的确存在的话。
 The sun is thought to possibly be a factory for these axions. When photons at the sun's core feel a magnetic field, they become axions, the thinking goes. Since the teensy particles only weakly interact with ordinary matter, they are thought to easily fly through the sun's core toward the surface unimpeded by other particles. Once at the solar corona, where the sun's magnetic field is strong, the axions would convert back into photons.  研究人员认为,太阳可能是制造轴子的工厂。他们的想法是这样的:当太阳核心部位的光子遇到磁场时,这些光子就会变成轴子。由于跟普通物质之间只是发生微弱的相互作用,这些微小的轴子能够很容易地穿过太阳核心,朝着表面飞去,不会受到其他粒子的阻拦。一旦到达太阳磁场强烈的日冕处,这些轴子又会转变为光子。
 It's these photons that Hudson's team hopes to find using existing instruments on three satellites capable of observing solar X-rays: Yohkoh, RHESSI  and Hinode. 赫德森研究小组希望发现的正是这些光子,他们利用了三颗人造卫星上的现有仪器。三颗人造卫星分别是:“阳光”号卫星,“拉马第高能太阳分光镜成像”卫星和“日出”号卫星,均可以用来观察日光中的X射线。
 The X-ray images to date, Hudson said, have turned up empty of axion signatures. He and his team hope to increase the sensitivity of their searches by combining lots of images to yield, potentially, a stronger, composite signal. The composite image would help the astrophysicists to get rid of so-called background noise produced by everything else but the axions.  赫德森说,到目前为止从这些X射线图像上还没有发现轴子的信号。赫德森及同事希望通过把大量的图片结合到一起,来提高搜寻的灵敏度,从而有可能产生一种更为强烈的复合信号。这种合成图像将会有助于天体物理学家们摆脱由其他一切事物产生的所谓的背景噪声,只留下轴子信号。
 The search is on  搜寻在继续
 Other axion searches are ground-based. 对轴子的其他搜寻活动是在地面上的。
 The CERN Axion Solar Telescope in Geneva aims to detect axions from the sun's super-hot core. Hypothetically, the axions should hit the telescope's superconducting magnet (and associated magnetic field). The axions would transform back into photons due to the magnetic field. An X-ray detector would then pick up the X-ray signal of these photons.  欧洲粒子物理研究所位于日内瓦,该所的“太阳轴子望远镜”的目标是:发现来自太阳超高温核心的轴子。从假设的角度来说,轴子应该可以遇上这架望远镜的超导性磁体(以及联合磁场)。由于磁场的作用,这些轴子将会转变,再次成为光子。那么,X射线探测器将会捕捉到这些光子散发的X射线信号。
 And in the Axion Dark Matter Experiment at Lawrence Livermore National Laboratory in California, astrophysicist Karl van Bibber and his colleagues hope to create their own axions. They are manufacturing intense magnetic fields in the hopes of detecting microwave signals of an axion decaying into a single, real photon. 在加州劳伦斯利弗莫尔国家实验室进行的轴子暗物质实验中,天体物理学家卡尔·范·比伯及同事希望亲自创造出轴子。他们正在制造强磁场,希望能够检测出正在衰变成真实单一光子的轴子微波信号。
 "The axion is so light that it doesn't decay into two photons in free space. However, you can play a very remarkable trick," van Bibber said. "If I shoot a photon into a magnetic field (which you can think of as a sea of virtual photons), a real photon and a virtual photon [interact] to make an axion and vice versa." “轴子很轻,它不会在自由空间中衰变成两个光子。然而,我们可以耍一个非同寻常的花招,”范·比伯说,“如果我将一个光子射进磁场中,你可以将磁场当作是一个虚拟光子的海洋,那么一个真实光子和一个虚拟光子相互作用,可以变成一个轴子,反之亦然。”
 Pending award 悬而未决的情况
 Whether it's made of axions or WIMPs, or something else, the invisible stuff seems to be everywhere. 不管暗物质是由轴子构成的还是由弱作用重粒子构成的,或者是由其他粒子构成的,这种不可见物质好象是无处不在的。
 "Everyone in the business agrees that there is an unknown particle that is the dark matter of both the universe and of our galaxy," Tanner said. "Galaxies have a halo of dark matter, so their mass is much greater than the mass of the luminous stars in them." “参与这个领域研究的人们都一致认为,有一种未知的粒子构成了我们星系以及我们宇宙中的暗物质,”坦纳说,“星系拥有暗物质晕,所以它们的质量比其中发光恒星的质量要大得多。”
 If Hudson's or another team were to reel in axions, the announcement that they are the dark matter particle would not immediately follow. For one, evidence that axions exist would not exclude the existence of WIMPs, van Bibber said.  如果赫德森研究小组或另外一个研究小组参与到轴子的研究中来,并且宣布轴子就是暗物质粒子,他们的论断不会立刻被采纳的。范·比伯指出,证明轴子的存在并不排除弱作用重粒子的存在。
 "It might be that we live in a universe that is kind of a cocktail, that it might be 90 percent WIMPs and 10 percent axions, or fifty-fifty or something like that," van Bibber said. “我们生活于其中的宇宙可能是鸡尾酒式的结构,它有可能是由90%的弱作用重粒子和10%的轴子构成的,或者是两者平分秋色,或者大致是平分秋色,”范·比伯说。
 That's not ideal, of course. "Nobody knows and nobody is so dogmatic as to say that my type of dark matter is the only type," Tanner said. "One hopes there aren't thousands of types of dark matter because that makes the problem very messy." 当然这种结果并不理想。“谁也搞不清,谁也不会独断地说:‘我所研究出的这种暗物质是唯一正确的一种。’”坦纳说,“但是,我们不希望存在成千上万种暗物质,因为那样会使该问题变得凌乱不堪。”
 Love affair 犹如情爱
 Even with the odds of detecting dark matter not in their favor, astrophysicists maintain an unwavering optimism. 对于天体物理学家们来说,尽管发现暗物质的可能性并不大,但他们一贯保持着乐观的态度。
 "I think if one were not optimistic, one would probably throw in the towel. I think I'm an optimist about that. I think I expect someday the phone will ring and somebody will say 'Did you hear that so and so found the axion?'" van Bibber said during a telephone interview. "And they will do it in a clever way that we hadn't thought about. I'm expecting to be surprised, because it will be found in a pleasantly unsuspected way." “我认为,如果一个人不乐观,他很可能就会认输了。我想我对此是乐观的,我期望有朝一日电话铃响起的时候,有人会说:‘某某如何如何发现了轴子,你听说了吗?’”范·比伯在接受电话采访时说,“他们将会以一种巧妙的、出人意料的方式发现轴子。我期待着能有个惊喜,因为人们将会以一种令人愉快的意外方式发现轴子。”
 He describes his search for the axion as one involving romance. "Personally, it's like any love affair, you kind of get smitten," he said. "I've been smitten for about 20 years now." 范·比伯把自己对轴子的搜寻描述成犹如一个人陷入情爱之中。“对我个人来说,这就象一张情网,感觉有点象深深地为情所动,”他说,“到目前为止,我被深深地打动了约20年。”
 For Hudson, solar axions hold another prize, a window inside the sun.  对于赫德森来说,对太阳轴子的研究还会有另外一个收获——开启一扇观测太阳内部的窗口。
 "It would be revolutionary for solar and stellar physics to be able to make use of the axions, if real, to see inside the sun," Hudson said, "and also to study the coronal magnetic field via the conversion process [of axions to photons]." Axions could help astrophysicists to make more accurate measurements of the temperature of the sun's core, for instance. 赫德森指出:“如果真正存在轴子的话,如果能够利用轴子来观测太阳内部,能够通过从轴子到光子的转变过程来研究日冕的磁场,那将会在太阳及恒星物理学领域掀起一场革命。”比如,赫德森或许能够帮助天体物理学家们更加精确地测量出太阳核心的温度。
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