１３个最伟大的天文发现（下）_世界上最伟大的天文家

　　为纪念伽利略首次使用望远镜进行天文观测400周年,在国际天文学联合会和联合国教科文组织的共同倡议下,联合国大会将2009年正式定为国际天文年,并将其主题定为“探索我们的宇宙”。终于迎来最后三个发现了!小编们松了一口气,估计同学们也大呼“解脱”了吧?持续三期的专题内容,啃下来虽然有点吃力,但本次专题确实是不错的语音和写作学习材料―把这上、中、下三期文章的声音连着脱稿听一遍,学习主持人如何将13个天文发现完美无瑕、环环相扣地娓娓道来。同学们也不妨边听边做记录,试着根据笔记将发现者及发现内容按照时间顺序简要复述出来。前两期发现内容请查阅CE: Teens 2009年7、8月号。
　　
　　Gamma Ray Bursts
　　Discoverer: U.S. scientists
　　The coming of the “space age” ushered[引领] in a golden age of astronomy that is still going on today. That golden age began, strangely enough, not in space but with the turning point in cold war relations, that also contributed to our next great discovery.
　　In the 1960s, despite a nuclear test ban treaty, The Soviet Union refused to allow on-site[现场的] inspectors at its nuclear facilities. As a result, the U.S. opted[选择]
　　to monitor the Soviets by developing an orbital satellite
　　system, capable of detecting gamma ray bursts
　　produced by nuclear explosions. Because the satellite’s detectors looked up as well as down, scientists decided to use them to see if supernovae[超新星] produced gamma rays when they exploded. Between 1969 and 1972, they detected evidence of 16 short gamma ray bursts scattered across the sky. There was just one problem. None of the bursts correlated[相互关联] with any of the known supernova events. And the mystery deepened.
　　Over the next two decades, astronomers detected an average of one gamma ray burst a day, but each burst happened so quickly that it was over before astronomers could get a telescope aimed at it. Finally, astronomers
　　began to solve the puzzle with the help of the BeppoSAX注1
　　space telescope, which was designed specifically to
　　detect short bursts of gamma and X-rays and precisely pinpoint[精确定位] their locations.
　　On December 14th, 1997, BeppoSAX located a gamma ray burst, leading to the first photographs ever taken of a burst in wavelengths other than gamma. To their astonishment, astronomers discovered that the burst took place in a galaxy 12 billion light years away, making
　　it one of the universe’s most powerful explosions. Since then, dozens of other gamma ray bursts have been
　　similarly documented, all just as powerful and far away. As for what it all means, the discovery of gamma ray bursts have once again shown us that, hidden out there behind the veil of the earth’s atmosphere are objects that are not only strange and hard to fathom[进行探测] � black holes, pulsars[脉冲星], quasars[类星体] � but they’re lethal[致命的], too. Gamma ray bursts are now considered a possible cause of past extinction events on earth.
　　The scientist Sir Arthur Eddington once noted, “Not only is the universe stranger than we imagine, it is stranger than we can imagine.” He could have been
　　talking about gamma ray bursts, the expanding universe or the theory of general relativity. It also happens to be a perfect description of our next discovery.
　　
　　Planets Orbiting Other Stars
　　Discoverer: Alexander Wolszczan, Geoffrey Marcy and other scientists
　　Once, it would have been impossible for
　　astronomers to imagine discovering other solar systems with planets like our own. But today, astronomers can imagine, thanks to powerful space- and ground-based telescopes like the one here at the Lick Observatory in Mount Hamilton, California, where Jeff Marcy is hunting for new planets.
　　Nye: How do you go about finding a planet around a star?
　　Marcy: Well, it’s very easy. We watch the star to see if it wobbles[摇摆] in response to the planet yanking[猛拉] on it gravitationally.
　　Nye: Oh, you just need one of these.
　　Marcy: That’s right. This is the three-meter Lick
　　Observatory telescope.
　　The search for extra-terrestrial[地球的] planetary systems gained momentum[气势] in the early 1990s, when a Polish astronomer made a surprising discovery.
　　Marcy: There’s a wonderful discovery by Alex Wolszczan of a system of three planets orbiting a pulsar, and the way he found them was quite
　　exciting. He watches the pulses coming from the
　　pulsar, and the arrival of those pulses changes as the pulsar approaches and recedes[后退] us. These are hideous[可怕的] stars. Pulsars
　　have ultraviolet[紫外线辐射],
　　X-rays and gamma rays coming off them. They’re the bizarre[奇异的] end products of a supernova explosion, and despite that bizarre
　　environment, here we have earth-sized planets going around it. If there’re earth-size planets around pulsars, you can bet there are earth-size planets around other stars.
　　Since Wolszczan’s discovery, Marcy and other astronomers have found more than 130 extra-solar planets.
　　Marcy: We thought we would never find even one planet, and we have found the world’s only
　　triple[由三个部分组成的] planet system and quad-
　　ruple[由四个部分组成的] planet system with this telescope. These are planets the size of our Jupiter, Saturn, and the smallest are Neptune-sized, so it’s quite exciting. We’re finding planets of Jupiter size, but even those a few times bigger than the earth.
　　While no earth-like planets have yet been found, the search continues.
　　
　　The Universe Is Accelerating
　　Discoverer: Saul Perlmutter and other scientists
　　As the universe expanded following the Big Bang, logic dictated that the gravitational attraction of all matter should pull at that expanding material and cause the expansion to slow. But how much was the universe slowing down? In the 1990s the Hubble space telescope made it possible
　　for teams of scientists to answer the question by studying the brightness of light from a special type of exploding star called a Type 1-A supernova.
　　I paid a visit to the
　　Lawrence Berkley National Laboratory in San Francisco,
　　and met with astrophysicist Saul Perlmutter, who
　　headed-up the Supernova Cosmology Project.
　　Nye: So what did you find out?
　　Perlmutter: So we started to make a measurement to try to find out how much the universe, in its extension, is slowing down. When we first saw the data, you…you say, “Well, that’s kind of funny. It kinda looks as if the universe isn’t…isn’t slowing down.” You check each step of the process, and little by little, it really looks like the universe is actually speeding up. This acceleration of the universe doesn’t fit at all. We understand pretty well what all the forces are in the universe and what all the objects are in the universe, and this is one of the first times that we’ve come across something that we wouldn’t have predicted.
　　Nye: Why is it accelerating?
　　Perlmutter: Well, that’s the question that has us all dying to know the answer, and, I mean, one way to think about it is that if you have a[n] energy, of this odd sort that would pervade[遍及] all of space, it can actually speed up [the] universe where gravity’s trying to slow it down. And we’re calling that “dark energy,” just to
　　reflect the fact that we don’t know what it is.
　　Here we have SNAP注2 that we’re hoping to be able to launch in the not-too-distant future. This one goes out to a location out past the moon. From that vantage point[有利位置]
　　you can measure the expansion history with such detail that we could actually see the little changes, when it goes from
　　deceleration[减速] to acceleration. Back when the universe was
　　really dense and close together, gravity was more important and it slowed the expansion down. As it kept expanding, though, even slower and slower, it lost out and gravity became less important than the dark energy, which took over and started to accelerate
　　the expansion. And we’re after exactly how that changeover
　　occurred, and that will tell us about what different possible
　　theories could be right, to explain the dark energy.
　　Nye: Always expanding…
　　Perlmutter: Exactly.
　　Nye: …but slowly then speeding up.
　　Perlmutter: Exactly.
　　Nye: And that’s where we are now.
　　Perlmutter: Exactly. So it’s this issue of… “Did it slow down and then suddenly spurt[突然急速行进]? Or did it slow and come to a
　　wobble and then take off?” You know, what…what was that
　　transition like?
　　Just like the ancient astronomers, modern scientists have discovered something about the cosmos that we can not yet
　　explain. It’ll be up to observers and theorists to figure out what’s
　　going on in our expanding universe. For this, they’ll need new ideas and better instruments. Now, whether this mystery is solved soon or far in the future, you can be certain of one thing �
　　we will keep watching the skies to understand our place in the cosmos. We will continue to explore, understand and discover.
　　
　　伽玛射线爆发
　　发现者:美国科学家
　　“太空时代”的来临开启了天文学的黄金时代,至今方兴未艾。但奇怪的是,这个黄金时代的开始并非来自太空,而是来自冷战时期美苏关系的转折点。这也促成了我们的下一个伟大发现。
　　20世纪60年代,虽然有禁止核试验条约,苏联拒绝让实地考察员进入其核能设施检查。因此,为了监察苏联的动态,美国开发出一套轨道卫星系统,用以探测核爆产生的伽玛射线。由于卫星探测器可以对其上空和下空进行探测,科学家决定用其观测超新星爆炸时会否产生伽玛射线。1969到1972年间,他们探测到16次分散于星空的短伽玛射线爆发。问题在于,没有一次爆炸与已知的超新星有关。谜团越来越深。
　　在往后20年里,天文学家平均每天都能探测到一次伽玛射线爆发,但每次爆发都异常迅速,他们根本来不及用望远镜瞄准它。最后,天文学家借助比普卫星才得以解开这些疑问。这个卫星专门用于探测伽玛射线及X射线的短爆发,并能准确定位爆发位置。
　　1997年12月14日,比普卫星找到了一次伽玛射线爆发的位置,从而拍摄到第一批伽玛射线以外的、其他波长射线爆发的照片。天文学家们惊讶地发现,这次爆炸发生在120亿光年之外的星系中,是宇宙中威力最强大的爆炸之一。随后,天文学家又记录到数十个伽玛射线爆发事件,它们具有同等强大的威力,距离我们都很远。这一发现的意义在于――伽玛射线爆发这个发现再度告诉我们,在地球大气之外的外太空里藏着许多奇妙的星体,不仅难以测量――比如黑洞、脉冲星和类星体,而且其威力足以致命。现在,伽玛射线爆发被认为可能是其中一个造成古代地球生物
　　灭亡的原因。
　　(英国)科学家亚瑟・艾丁顿曾说:“宇宙的奇妙不仅超出我们的想象,甚至是我们远远无法想象的。”他所说的话既可以用来形容伽玛射线爆发、宇宙膨胀或广义相对论,也能贴切地概括我们的下一个伟大发现。
　　
　　行星绕行其他恒星
　　发现者:亚历山大・沃尔兹刚、
　　杰弗里・马西及其他科学家
　　过去,天文学家们根本想不到人类会发现其他拥有像地球这样的行星的太阳系。但如今,多亏了太空及地表高倍望远镜――例如(美国)加利福尼亚州汉密尔顿山利克天文台的这具望远镜,天文学家能够尽情想象(这样的星象)。杰夫・马西在此寻找新行星。
　　纳尔:你如何寻找绕行恒星的行星?
　　马西:这很简单。我们观察恒星,看其是否因应行星重力的拉扯而摆动。
　　纳尔:噢,你只要借助这么一个
　　大家伙。
　　马西:没错。这是口径为3米的利克
　　天文望远镜。
　　20世纪90年代初期,寻找太阳系外行星系的势头日渐增大,因为当时一位波兰天文学家有一个惊人的发现。
　　马西:天文学家亚历克斯・沃尔兹刚有一个伟大的发现,他发现了一个有三颗行星绕行一颗脉冲星的星体系统,而且他发现的方式也相当令人振奋。他观测来自脉冲星的脉冲,而那些脉冲抵达时(的状况)会随着脉冲星接近或远离我们而改变。这是些很可怕的星体。脉冲星能放射出紫外线、X射线和伽玛射线。它们是超新星爆炸后怪异的最终产物,虽然环境奇异,我们却发现有一些和地球体积相当的行星围绕它运行。假若有地球大小的行星绕行脉冲星,你就可以肯定有地球大小的行星绕行其他恒星了。
　　继沃尔兹刚的发现之后,马西及其他天文学家又发现了超过130个太阳系外
　　行星。
　　马西:我们原本以为不可能发现任何行星,但藉由这具天文望远镜,我们发现了宇宙中唯一一个三连颗系外行星以及四连颗系外行星。这些行星的大小相当于我们太阳系的木星和土星,最小的也有海王星那么大,因此这是一项让人兴奋的发现。我们正在寻找木星大小的行星,但即使那样的行星还是比地球大好几倍。
　　只要仍未找到像地球一样的行星,寻觅工作仍将继续下去。
　　
　　宇宙加速膨胀
　　发现者:索尔・普密特及其他科学家
　　大爆炸之后,宇宙不断向外扩张。理论上,物质间的引力会对物质的膨胀起到牵制作用,减慢其膨胀速度。然而宇宙膨胀的速度到底减缓了多少?上世纪90年代,哈勃太空望远镜让科学家们得以解开这个疑虑――方法是研究某种特别的爆炸恒星,也就是1A型超新星的
　　亮度。
　　我造访
　　了(美国)旧金山的劳伦斯伯克利国家实验室,前去拜访天体物理学家
　　索尔・普密特。他是“超新星宇宙学计划”的带头人。
　　纳尔:请问您发现了什么?
　　普密特:一开始,我们进行了测量,尝试找出宇宙膨胀减缓的程度。第一次看到那些数据时,我们想:“真奇怪,宇宙似乎没有减慢膨胀的速度。”在检查过计算的每一个步骤之后,渐渐地,我们发现宇宙真的正在加速膨胀。宇宙的这种膨胀并不合理。我们已经很清楚宇宙中的各种力量以及宇宙中存在什么星体,这是我们第一次遇到超出预测的
　　东西。
　　纳尔:为什么宇宙会加速膨胀呢?
　　普密特:这就是我们竭尽全力试图解答的问题,我的意思是,你可以这么想,假如有一种怪异的能量遍布整个太空,它能加速宇宙膨胀的速度――尽管引力却试图给膨胀减速。我们把它称为“暗能量”,意思是目前我们还不知道它是一种怎样的能量。
　　这是超新星加速探测器,我们希望能在不久的将来将其发射升空。它升空后将飞越月球到达某个定点。在那个位置上,你可以详细测量宇宙的膨胀史,这样我们就可以观测到其从减速到加速的微小变化。过去宇宙密度很高的时候,星体之间非常贴近,引力占据主导地位,可以减缓宇宙膨胀。随着宇宙继续膨胀,速度越来越慢,最终停止,那时引力的重要性就比不上暗能量,暗能量就会取代引力,加速宇宙膨胀。我们正在追寻这种改变究竟是如何发生的,这样我们就能知道哪些不同的理论可能正确解释
　　暗能量。
　　纳尔:一直在膨胀……
　　普密特:是的。
　　纳尔:……但减速后再次加速膨胀。
　　普密特:没错。
　　纳尔:这就是我们所处的状态。
　　普密特:完全正确。因此问题就在于……“(宇宙)到底是先减速然后突然加速?还是减速后经历一个拉锯过程再急速膨胀呢?”你知道,这种变迁究竟是怎样的呢?
　　就像古代天文学家一样,现代科学家已经发现了一些目前无法解释的宇宙现象。这个重任将落在观测者及理论家身上,他们要弄明白膨胀中的宇宙里到底发生了什么事情。他们需要新观念和更好的观测仪器来追寻答案。无论这个谜团的解答会出现在不久的将来还是遥遥无期,我们可以肯定的是――人类会继续观测天空,从而了解自身在宇宙中的定位。我们会一直坚持探索和了解,继续发现。
　　
　　注1:比普卫星(BeppoSAX)是一颗由多间意大利与荷兰公司合作研制出的、用于X射线研究的卫星,于1996年4月30日发射升空,原定两年的服务年限被延长至6年,2003年4月29日脱离轨道跌落太平洋。其名字中的“Beppo”以意大利天体物理学家吉斯珀・比普・奥克利尼(Giuseppe Beppo Occhialini)命名,而“SAX”是意大利语“Satellite per Astronomia a raggi X”,即“Satellite for X-ray astronomy”。
　　注2:超新星加速探测器(Supernova Acceleration Probe)的缩写。