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演说者：Tabetha Boyajian 演说题目：宇宙中最诡异的恒星！ 一个巨大、地球1000倍大小的物体遮蔽了遥远的一颗名为KIC 8462852的星星，但没人可以确知那是什么样的物体。在天文学家塔贝莎．菠耶金调查这颗巨大、奇特的物体可能是什么的时候，她的一位同事有个奇特的猜想：会不会是外星文明盖的巨型建筑结构呢？这样超凡的想法，需要超凡的证据。这场演讲，菠耶金将带我们一起来看看面对未知事物时，科学家如何研究和验证假说。 Extraordinary claims require extraordinary evidence, and it is my job, my responsibility, as an astronomer to remind people that alien hypotheses should always be a last resort. 00:29 Now, I want to tell you a story about that. It involves data from a NASA mission, ordinary people and one of the most extraordinary stars in our galaxy. 00:41 It began in 2009 with the launch of NASA's Kepler mission. Kepler's main scientific objective was to find planets outside of our solar system. It did this by staring at a single field in the sky, this one, with all the tiny boxes. And in this one field, it monitored the brightness of over 150,000 stars continuously for four years, taking a data point every 30 minutes. It was looking for what astronomers call a transit. This is when the planet's orbit is aligned in our line of sight, just so that the planet crosses in front of a star. And when this happens, it blocks out a tiny bit of starlight, which you can see as a dip in this curve. 01:31 And so the team at NASA had developed very sophisticated computers to search for transits in all the Kepler data. 01:39 At the same time of the first data release, astronomers at Yale were wondering an interesting thing: What if computers missed something? 01:52 And so we launched the citizen science project called Planet Hunters to have people look at the same data. The human brain has an amazing ability for pattern recognition, sometimes even better than a computer. However, there was a lot of skepticism around this. My colleague, Debra Fischer, founder of the Planet Hunters project, said that people at the time were saying, 'You're crazy. There's no way that a computer will miss a signal.' And so it was on, the classic human versus machine gamble. And if we found one planet, we would be thrilled. When I joined the team four years ago, we had already found a couple. And today, with the help of over 300,000 science enthusiasts, we have found dozens, and we've also found one of the most mysterious stars in our galaxy. 02:44 So to understand this, let me show you what a normal transit in Kepler data looks like. On this graph on the left-hand side you have the amount of light, and on the bottom is time. The white line is light just from the star, what astronomers call a light curve. Now, when a planet transits a star, it blocks out a little bit of this light, and the depth of this transit reflects the size of the object itself. And so, for example, let's take Jupiter. Planets don't get much bigger than Jupiter. Jupiter will make a one percent drop in a star's brightness. Earth, on the other hand, is 11 times smaller than Jupiter, and the signal is barely visible in the data. 03:26 So back to our mystery. A few years ago, Planet Hunters were sifting through data looking for transits, and they spotted a mysterious signal coming from the star KIC 8462852. The observations in May of 2009 were the first they spotted, and they started talking about this in the discussion forums. 03:47 They said and object like Jupiter would make a drop like this in the star's light, but they were also saying it was giant. You see, transits normally only last for a few hours, and this one lasted for almost a week. 04:01 They were also saying that it looks asymmetric, meaning that instead of the clean, U-shaped dip that we saw with Jupiter, it had this strange slope that you can see on the left side. This seemed to indicate that whatever was getting in the way and blocking the starlight was not circular like a planet. There are few more dips that happened, but for a couple of years, it was pretty quiet. 04:26 And then in March of 2011, we see this. The star's light drops by a whole 15 percent, and this is huge compared to a planet, which would only make a one percent drop. We described this feature as both smooth and clean. It also is asymmetric, having a gradual dimming that lasts almost a week, and then it snaps right back up to normal in just a matter of days. 04:52 And again, after this, not much happens until February of 2013. Things start to get really crazy. There is a huge complex of dips in the light curve that appear, and they last for like a hundred days, all the way up into the Kepler mission's end. These dips have variable shapes. Some are very sharp, and some are broad, and they also have variable durations. Some last just for a day or two, and some for more than a week. And there's also up and down trends within some of these dips, almost like several independent events were superimposed on top of each other. And at this time, this star drops in its brightness over 20 percent. This means that whatever is blocking its light has an area of over 1,000 times the area of our planet Earth. 05:46 This is truly remarkable. And so the citizen scientists, when they saw this, they notified the science team that they found something weird enough that it might be worth following up. And so when the science team looked at it, we're like, 'Yeah, there's probably just something wrong with the data.' But we looked really, really, really hard, and the data were good. And so what was happening had to be astrophysical, meaning that something in space was getting in the way and blocking starlight. And so at this point, we set out to learn everything we could about the star to see if we could find any clues to what was going on. And the citizen scientists who helped us in this discovery, they joined along for the ride watching science in action firsthand. 06:36 First, somebody said, you know, what if this star was very young and it still had the cloud of material it was born from surrounding it. And then somebody else said, well, what if the star had already formed planets, and two of these planets had collided, similar to the Earth-Moon forming event. Well, both of these theories could explain part of the data, but the difficulties were that the star showed no signs of being young, and there was no glow from any of the material that was heated up by the star's light, and you would expect this if the star was young or if there was a collision and a lot of dust was produced. And so somebody else said, well, how about a huge swarm of comets that are passing by this star in a very elliptical orbit? Well, it ends up that this is actually consistent with our observations. But I agree, it does feel a little contrived. You see, it would take hundreds of comets to reproduce what we're observing. And these are only the comets that happen to pass between us and the star. And so in reality, we're talking thousands to tens of thousands of comets. But of all the bad ideas we had, this one was the best. And so we went ahead and published our findings. 08:00 Now, let me tell you, this was one of the hardest papers I ever wrote. Scientists are meant to publish results, and this situation was far from that. And so we decided to give it a catchy title, and we called it: 'Where's The Flux?' I will let you work out the acronym. 08:22 So this isn't the end of the story. Around the same time I was writing this paper, I met with a colleague of mine, Jason Wright, and he was also writing a paper on Kepler data. And he was saying that with Kepler's extreme precision, it could actually detect alien megastructures around stars, but it didn't. And then I showed him this weird data that our citizen scientists had found, and he said to me, 'Aw crap, Tabby. Now I have to rewrite my paper.' 08:54 So yes, the natural explanations were weak, and we were curious now. So we had to find a way to rule out aliens. So together, we convinced a colleague of ours who works on SETI, the Search for Extraterrestrial Intelligence, that this would be an extraordinary target to pursue. We wrote a proposal to observe the star with the world's largest radio telescope at the Green Bank Observatory. 09:20 A couple months later, news of this proposal got leaked to the press and now there are thousands of articles, over 10,000 articles, on this star alone. And if you search Google Images, this is what you'll find. 09:39 Now, you may be wondering, OK, Tabby, well, how do aliens actually explain this light curve? OK, well, imagine a civilization that's much more advanced than our own. In this hypothetical circumstance, this civilization would have exhausted the energy supply of their home planet, so where could they get more energy? Well, they have a host star just like we have a sun, and so if they were able to capture more energy from this star, then that would solve their energy needs. So they would go and build huge structures. These giant megastructures, like ginormous solar panels, are called Dyson spheres. 10:22 This image above are lots of artists' impressions of Dyson spheres. It's really hard to provide perspective on the vastness of these things, but you can think of it this way. The Earth-Moon distance is a quarter of a million miles. The simplest element on one of these structures is 100 times that size. They're enormous. And now imagine one of these structures in motion around a star. You can see how it would produce anomalies in the data such as uneven, unnatural looking dips. 10:58 But it remains that even alien megastructures cannot defy the laws of physics. You see, anything that uses a lot of energy is going to produce heat, and we don't observe this. But it could be something as simple as they're just reradiating it away in another direction, just not at Earth. 11:22 Another idea that's one of my personal favorites is that we had just witnessed an interplanetary space battle and the catastrophic destruction of a planet. Now, I admit that this would produce a lot of dust that we don't observe. But if we're already invoking aliens in this explanation, then who is to say they didn't efficiently clean up all this mess for recycling purposes? 11:50 You can see how this quickly captures your imagination. 11:55 Well, there you have it. We're in a situation that could unfold to be a natural phenomenon we don't understand or an alien technology we don't understand. Personally, as a scientist, my money is on the natural explanation. But don't get me wrong, I do think it would be awesome to find aliens. Either way, there is something new and really interesting to discover. 12:23 So what happens next? We need to continue to observe this star to learn more about what's happening. But professional astronomers, like me, we have limited resources for this kind of thing, and Kepler is on to a different mission. 12:39 And I'm happy to say that once again, citizen scientists have come in and saved the day. You see, this time, amateur astronomers with their backyard telescopes stepped up immediately and started observing this star nightly at their own facilities, and I am so excited to see what they find. 13:03 What's amazing to me is that this star would have never been found by computers because we just weren't looking for something like this. And what's more exciting is that there's more data to come. There are new missions that are coming up that are observing millions more stars all over the sky. 13:26 And just think: What will it mean when we find another star like this? And what will it mean if we don't find another star like this? 13:37 Thank you. 00:12 非同寻常的结论 需要非同寻常的证据。 作为天文学家， 这是我的职责和责任 去提醒人们外星人假说 一直都该是最后一根救命稻草。 00:29 现在，我要给你们 讲这么一个故事。 故事中有来自 NASA 项目中的数据， 有普通人，还有一颗 银河系里最非同寻常的星星。 00:41 故事开始于 2009 年， NASA 启动了开普勒计划。 开普勒计划的 首要科学目标 是寻找太阳系以外的行星。 它持续观测一小块天区， 就这块，所有这些小方块。 在这小块区域中， 它持续观测超过 15 万颗恒星的亮度， 整整四年， 每 30 分钟就采集一次数据。 它在搜寻天文学家 叫做掩食的东西。 它发生在行星轨道和 我们的观测视线重合情况。 这样，行星就会 从恒星前面经过。 这种情况下，行星 就会挡住一点点的星光。 你可以在光度曲线上 看到小小的负峰。 01:31 于是 NASA 团队开发出 非常复杂的电脑程序， 来搜寻开普勒 数据中的掩食事件。 01:39 在首次数据发布的同时， 耶鲁大学的天文学家 在考虑一个有趣的问题： 万一电脑错过了什么怎么办？ 01:52 于是，我们又发起了一项 名为“行星猎人”的公民科学项目。 这个项目依靠大众 来分析同样的数据。 人脑有着惊人的模式识别能力， 有时候甚至比电脑都厉害。 然而，这个项目 遭到了很多质疑。 我的同行，黛布拉·费舍尔， 行星猎人项目的发起人， 说那时候人们议论道： “你们疯了。 电脑绝不可能错过信号。” 所以这又是人和机器 赌哪个的老段子。 如果我们发现了一颗行星， 那我们就会特别高兴。 四年前， 在我加入这个团队的时候， 我们已经有了发现。 而今天，通过超过 30 万 科学爱好者的努力， 我们已经发现了数十颗行星， 而且我们发现了 这一颗银河系中 最最奇异的恒星。 02:44 为了说清楚， 请看一下开普勒数据中 一次正常的掩食是什么样子。 这幅图中，左边轴是光强度， 底下的横轴是时间。 这条白线是单纯来自恒星的光， 天文学家称为光度曲线。 现在，当一颗行星掩过恒星， 它阻挡了一点点星光， 而这个掩食的深度 反映了行星体自身的大小。 所以，例如木星。 行星通常不太会 比木星还要大。 木星会减弱百分之一的星光。 换做地球， 地球只有木星的 1/11 大， 它的信号在数据中几乎看不见。 03:26 回到我们的谜题。 几年前，行星猎人 正在筛选数据寻找掩食， 他们发现了一个诡异的信号 来自恒星 KIC 8462852。 2009 年五月是他们 首次发现这个信号， 他们开始在论坛中 讨论这个发现。 03:47 他们说一个类似木星的星体 可以造成这样的星光削弱， 但他们也说这家伙太大了。 你看，掩食通常只持续几个小时， 而这一个持续了将近一周。 04:01 他们也在说谱线看起来不对称， 这是说，不像木星那样 有一个干净、U 型的负峰， 大家看，这条数据左侧 的倾斜度很奇怪。 这似乎意味着， 无论闯进来 挡住星光的是什么东西， 它不会像行星那样是个球形。 后来陆续还有少量的负峰， 但这颗星在之后的一两年 一直都没什么动静。 04:26 然后在 2011 年三月， 我们观察到了这个。 这颗恒星的光度 掉了整整 15%， 这比一颗行星能造成的大太多了， 行星只能造成 1% 的光度下降。 我们把这条谱线特征 描述为光滑和干净。 它也是不对称的， 在持续近一周的时间内 逐步减弱， 然后在一两天内 立马反弹回正常的光度。 04:52 在此之后，又是什么都没发生， 直到 2013 年二月。 事情的发展完全出乎意料。 光度曲线上出现了 一大群复杂的负峰， 而且它们持续了 差不多一百天， 一直延续到 开普勒计划结束。 这些负峰有着各种形状。 有一些很尖锐， 有一些很宽， 以及有不同的持续时间。 有一些只持续一两天， 有的则超过一周。 而且在一些光度负峰中， 还出现上上下下的起伏， 感觉好像是几个独立事件 重叠在一起。 而且这次，这颗恒星的亮度 下降了超过 20%。 这说明不管是什么东西 挡住了光， 这家伙有着超过地球 1000 倍的面积。 05:46 这真心是非同寻常。 当公民科学家发现这个时， 他们通知了科学家团队， 称他们发现了足够奇怪的东西 可能值得后续跟进研究。 于是当科学家团队看过数据之后， 我们觉得：“好吧，会不会 只是数据有点问题。” 不过经过我们非常、 非常、非常仔细的调查， 数据没有问题。 因此，出现这些负峰一定有 天体物理学的原因， 说明太空中有什么东西 经过了我们和恒星之间， 挡住了它的光。 这个时候， 我们竭力研究 关于这颗恒星的一切， 希望能找到任何 可以解释这些现象的线索。 帮助我们发现这颗星的 公民科学家， 也加入了讨论， 见证科学第一线的行动。 06:36 首先，有人提出， 是不是这颗星非常年轻， 它仍旧保有它诞生之时 周围的星际云物质。 另外有人说， 好吧，是不是这颗星 已经形成了行星系统， 而两颗行星相撞了， 就像地球——月球的形成过程。 好吧，这两种假说 都可以解释部分数据， 但是困难在于，这颗恒星 没有显示任何年轻的特征， 而且也没有来自任何物质 被星光加热发出的光晕。 如果恒星年轻， 或者碰撞产生大量尘埃， 通常会出现这种现象。 又有人说， 好吧，会不会是一大群彗星呢 在一个非常椭圆的轨道上 一连串地穿过这颗恒星？ 好吧，这个假说倒是 和我们的观测相吻合。 但是我同意， 这感觉有点牵强。 你看，需要数百颗彗星， 才能重现我们的观测。 而这些只是 恰好从我们和恒星 中间穿过的彗星。 所以实际情况下， 将会有成千上万颗彗星。 但是在我们所有的烂解释中， 这个算是最好的了。 于是我们发表了我们的发现。 08:00 要我说，这是我写过的 最困难的论文之一。 科学家理应发表明确的结果， 而这次我们离结果 还有十万八千里呢。 所以我们决定 起一个抓眼球的标题， 我们的题目是： 《光去了哪里》 麻烦大家自行意会这个梗 08:17 （笑声。标题的英文缩写为 WTF，即“什么鬼”） 08:22 不过这故事还没完呢。 在我写这篇论文的同时， 我见了一位同行， 贾森·莱特 他也在写一篇 有关开普勒数据的论文。 他说道，从开普勒 无与伦比的精度来看， 它其实可以探测到 恒星周围的外星人建筑， 但是并没有发现。 然后我给他看了这个由我们 公民科学家发现的奇怪数据， 然后他对我说， “见鬼，塔碧。 这下我论文得重写了。” 08:54 所以，没错， 自然解释很牵强， 我们很好奇。 我们必须找到一个 排除外星人的方法。 于是我俩一起说服了 我们在 SETI（寻找地外 文明计划）工作的一位同行， 说这是一个非常 出色的追逐目标。 我们起草了一份 观测这颗恒星的项目书 请求使用绿岸天文台的 世界上最大的射电天文望远镜。 09:20 两三个月后， 这份项目书的消息 被媒体刺探到了 好吧，现在有几千篇报道 可能超过一万篇， 单单关于这颗恒星。 如果你用谷歌图片搜索， 你会找到这些。 09:39 现在，观众可能会问， 好吧塔碧， 究竟怎么用外星人 去解释这光度曲线？ 好吧，想象一个 远比我们发达的文明， 在这个假设条件下， 这个文明肯定耗尽了 他们母星的能源。 所以他们从哪里 获取更多的能量？ 你看，他们有一颗宿主恒星， 就像我们有太阳一样， 那如果他们能够 从恒星中抓取更多能量， 那就可以解决 他们的能源需求。 所以他们可能会去 建造这些巨型建筑。 这些巨大的超级建筑， 比如巨大的太阳能电池板， 叫做“戴森球”。 10:22 上面这些图片 是许多艺术家想象中的戴森球。 很难去想象这些东西 究竟有多庞大， 但你可以这么想。 地球——月球间的距离 是四十万公里。 这些巨型结构中的 最简单的单元， 是 100 倍地月距离。 它们是庞然大物。 再想象，这样一个建筑 围绕着一颗恒星运动。 你可以看到这为什么 可以造成数据中异常 如此不对称，不自然的负峰。 10:58 但是即使是 外星人的超级建筑， 也不能违反物理定律。 任何使用大量能量的东西 将会产生热量， 但是我们没有观测到。 但这有可能只是非常简单的， 他们把热量释放到了另一个方向， 没有对着地球。 11:22 我个人最喜欢的 另一种可能性是 我们恰好目睹了 一场星球大战， 一颗行星被灾难性地 彻底摧毁了。 我承认， 这会产生很多尘埃， 然而我们没有观测到。 但是如果我们已经 在用外星人来解释， 那谁说他们不会秋风扫落叶 一般清理干净尘埃， 回收利用？ 11:50 你看，这很快 就激发想象力啦。 11:55 好啦，故事就是这样。 我们的处境是， 既可以解释成 我们没搞清楚的自然现象， 又可以解释成 我们没搞清楚的外星人科技。 作为科学家，我个人 还是会赌这是个自然现象。 但是别误解了，我绝对认同 能找到外星人非常棒。 不管怎样，有新东西， 非常有趣的东西等待发现。 12:23 那么，接下来呢？ 我们需要继续观测这颗恒星 去更详细地了解发生了什么。 然而，像我这样的职业天文学家， 我们在这方面的资源有限。 而开普勒望远镜已经在 执行另一项计划了。 所以我很高兴地说，又一次， 12:43 公民科学家加入进来救场。 你看，这次， 业余天文爱好者 拿着他们的业余望远镜 立刻加入进来， 开始在自己的观测点 夜观此星。 我非常期待他们的发现。 对我来说，激动人心的是 这颗恒星可能根本不会被电脑发现， 13:07 因为我们单纯没有把 这样的恒星当成目标。 更激动人心的是， 将来还有更多的数据。 有新的观测项目要上马， 准备观测百万颗恒星， 布满全天。 思考一下：如果我们又找到 一颗这样的恒星，意味着什么？ 13:32 而如果我们一颗都没找到， 那又意味着什么？ 谢谢。 |
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