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演說者：Tabetha Boyajian 演說題目：宇宙中最詭異的恒星！ 一個巨大、地球1000倍大小的物體遮蔽了遙遠的一顆名為KIC 8462852的星星，但沒人可以確知那是什么樣的物體。在天文學家塔貝莎．菠耶金調(diào)查這顆巨大、奇特的物體可能是什么的時候，她的一位同事有個奇特的猜想：會不會是外星文明蓋的巨型建筑結構呢？這樣超凡的想法，需要超凡的證據(jù)。這場演講，菠耶金將帶我們一起來看看面對未知事物時，科學家如何研究和驗證假說。 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 非同尋常的結論 需要非同尋常的證據(jù)。 作為天文學家， 這是我的職責和責任 去提醒人們外星人假說 一直都該是最后一根救命稻草。 00:29 現(xiàn)在，我要給你們 講這么一個故事。 故事中有來自 NASA 項目中的數(shù)據(jù)， 有普通人，還有一顆 銀河系里最非同尋常的星星。 00:41 故事開始于 2009 年， NASA 啟動了開普勒計劃。 開普勒計劃的 首要科學目標 是尋找太陽系以外的行星。 它持續(xù)觀測一小塊天區(qū)， 就這塊，所有這些小方塊。 在這小塊區(qū)域中， 它持續(xù)觀測超過 15 萬顆恒星的亮度， 整整四年， 每 30 分鐘就采集一次數(shù)據(jù)。 它在搜尋天文學家 叫做掩食的東西。 它發(fā)生在行星軌道和 我們的觀測視線重合情況。 這樣，行星就會 從恒星前面經(jīng)過。 這種情況下，行星 就會擋住一點點的星光。 你可以在光度曲線上 看到小小的負峰。 01:31 于是 NASA 團隊開發(fā)出 非常復雜的電腦程序， 來搜尋開普勒 數(shù)據(jù)中的掩食事件。 01:39 在首次數(shù)據(jù)發(fā)布的同時， 耶魯大學的天文學家 在考慮一個有趣的問題： 萬一電腦錯過了什么怎么辦？ 01:52 于是，我們又發(fā)起了一項 名為“行星獵人”的公民科學項目。 這個項目依靠大眾 來分析同樣的數(shù)據(jù)。 人腦有著驚人的模式識別能力， 有時候甚至比電腦都厲害。 然而，這個項目 遭到了很多質(zhì)疑。 我的同行，黛布拉·費舍爾， 行星獵人項目的發(fā)起人， 說那時候人們議論道： “你們瘋了。 電腦絕不可能錯過信號?！?所以這又是人和機器 賭哪個的老段子。 如果我們發(fā)現(xiàn)了一顆行星， 那我們就會特別高興。 四年前， 在我加入這個團隊的時候， 我們已經(jīng)有了發(fā)現(xiàn)。 而今天，通過超過 30 萬 科學愛好者的努力， 我們已經(jīng)發(fā)現(xiàn)了數(shù)十顆行星， 而且我們發(fā)現(xiàn)了 這一顆銀河系中 最最奇異的恒星。 02:44 為了說清楚， 請看一下開普勒數(shù)據(jù)中 一次正常的掩食是什么樣子。 這幅圖中，左邊軸是光強度， 底下的橫軸是時間。 這條白線是單純來自恒星的光， 天文學家稱為光度曲線。 現(xiàn)在，當一顆行星掩過恒星， 它阻擋了一點點星光， 而這個掩食的深度 反映了行星體自身的大小。 所以，例如木星。 行星通常不太會 比木星還要大。 木星會減弱百分之一的星光。 換做地球， 地球只有木星的 1/11 大， 它的信號在數(shù)據(jù)中幾乎看不見。 03:26 回到我們的謎題。 幾年前，行星獵人 正在篩選數(shù)據(jù)尋找掩食， 他們發(fā)現(xiàn)了一個詭異的信號 來自恒星 KIC 8462852。 2009 年五月是他們 首次發(fā)現(xiàn)這個信號， 他們開始在論壇中 討論這個發(fā)現(xiàn)。 03:47 他們說一個類似木星的星體 可以造成這樣的星光削弱， 但他們也說這家伙太大了。 你看，掩食通常只持續(xù)幾個小時， 而這一個持續(xù)了將近一周。 04:01 他們也在說譜線看起來不對稱， 這是說，不像木星那樣 有一個干凈、U 型的負峰， 大家看，這條數(shù)據(jù)左側 的傾斜度很奇怪。 這似乎意味著， 無論闖進來 擋住星光的是什么東西， 它不會像行星那樣是個球形。 后來陸續(xù)還有少量的負峰， 但這顆星在之后的一兩年 一直都沒什么動靜。 04:26 然后在 2011 年三月， 我們觀察到了這個。 這顆恒星的光度 掉了整整 15%， 這比一顆行星能造成的大太多了， 行星只能造成 1% 的光度下降。 我們把這條譜線特征 描述為光滑和干凈。 它也是不對稱的， 在持續(xù)近一周的時間內(nèi) 逐步減弱， 然后在一兩天內(nèi) 立馬反彈回正常的光度。 04:52 在此之后，又是什么都沒發(fā)生， 直到 2013 年二月。 事情的發(fā)展完全出乎意料。 光度曲線上出現(xiàn)了 一大群復雜的負峰， 而且它們持續(xù)了 差不多一百天， 一直延續(xù)到 開普勒計劃結束。 這些負峰有著各種形狀。 有一些很尖銳， 有一些很寬， 以及有不同的持續(xù)時間。 有一些只持續(xù)一兩天， 有的則超過一周。 而且在一些光度負峰中， 還出現(xiàn)上上下下的起伏， 感覺好像是幾個獨立事件 重疊在一起。 而且這次，這顆恒星的亮度 下降了超過 20%。 這說明不管是什么東西 擋住了光， 這家伙有著超過地球 1000 倍的面積。 05:46 這真心是非同尋常。 當公民科學家發(fā)現(xiàn)這個時， 他們通知了科學家團隊， 稱他們發(fā)現(xiàn)了足夠奇怪的東西 可能值得后續(xù)跟進研究。 于是當科學家團隊看過數(shù)據(jù)之后， 我們覺得：“好吧，會不會 只是數(shù)據(jù)有點問題?！?不過經(jīng)過我們非常、 非常、非常仔細的調(diào)查， 數(shù)據(jù)沒有問題。 因此，出現(xiàn)這些負峰一定有 天體物理學的原因， 說明太空中有什么東西 經(jīng)過了我們和恒星之間， 擋住了它的光。 這個時候， 我們竭力研究 關于這顆恒星的一切， 希望能找到任何 可以解釋這些現(xiàn)象的線索。 幫助我們發(fā)現(xiàn)這顆星的 公民科學家， 也加入了討論， 見證科學第一線的行動。 06:36 首先，有人提出， 是不是這顆星非常年輕， 它仍舊保有它誕生之時 周圍的星際云物質(zhì)。 另外有人說， 好吧，是不是這顆星 已經(jīng)形成了行星系統(tǒng)， 而兩顆行星相撞了， 就像地球——月球的形成過程。 好吧，這兩種假說 都可以解釋部分數(shù)據(jù)， 但是困難在于，這顆恒星 沒有顯示任何年輕的特征， 而且也沒有來自任何物質(zhì) 被星光加熱發(fā)出的光暈。 如果恒星年輕， 或者碰撞產(chǎn)生大量塵埃， 通常會出現(xiàn)這種現(xiàn)象。 又有人說， 好吧，會不會是一大群彗星呢 在一個非常橢圓的軌道上 一連串地穿過這顆恒星？ 好吧，這個假說倒是 和我們的觀測相吻合。 但是我同意， 這感覺有點牽強。 你看，需要數(shù)百顆彗星， 才能重現(xiàn)我們的觀測。 而這些只是 恰好從我們和恒星 中間穿過的彗星。 所以實際情況下， 將會有成千上萬顆彗星。 但是在我們所有的爛解釋中， 這個算是最好的了。 于是我們發(fā)表了我們的發(fā)現(xiàn)。 08:00 要我說，這是我寫過的 最困難的論文之一。 科學家理應發(fā)表明確的結果， 而這次我們離結果 還有十萬八千里呢。 所以我們決定 起一個抓眼球的標題， 我們的題目是： 《光去了哪里》 麻煩大家自行意會這個梗 08:17 （笑聲。標題的英文縮寫為 WTF，即“什么鬼”） 08:22 不過這故事還沒完呢。 在我寫這篇論文的同時， 我見了一位同行， 賈森·萊特 他也在寫一篇 有關開普勒數(shù)據(jù)的論文。 他說道，從開普勒 無與倫比的精度來看， 它其實可以探測到 恒星周圍的外星人建筑， 但是并沒有發(fā)現(xiàn)。 然后我給他看了這個由我們 公民科學家發(fā)現(xiàn)的奇怪數(shù)據(jù)， 然后他對我說， “見鬼，塔碧。 這下我論文得重寫了。” 08:54 所以，沒錯， 自然解釋很牽強， 我們很好奇。 我們必須找到一個 排除外星人的方法。 于是我倆一起說服了 我們在 SETI（尋找地外 文明計劃）工作的一位同行， 說這是一個非常 出色的追逐目標。 我們起草了一份 觀測這顆恒星的項目書 請求使用綠岸天文臺的 世界上最大的射電天文望遠鏡。 09:20 兩三個月后， 這份項目書的消息 被媒體刺探到了 好吧，現(xiàn)在有幾千篇報道 可能超過一萬篇， 單單關于這顆恒星。 如果你用谷歌圖片搜索， 你會找到這些。 09:39 現(xiàn)在，觀眾可能會問， 好吧塔碧， 究竟怎么用外星人 去解釋這光度曲線？ 好吧，想象一個 遠比我們發(fā)達的文明， 在這個假設條件下， 這個文明肯定耗盡了 他們母星的能源。 所以他們從哪里 獲取更多的能量？ 你看，他們有一顆宿主恒星， 就像我們有太陽一樣， 那如果他們能夠 從恒星中抓取更多能量， 那就可以解決 他們的能源需求。 所以他們可能會去 建造這些巨型建筑。 這些巨大的超級建筑， 比如巨大的太陽能電池板， 叫做“戴森球”。 10:22 上面這些圖片 是許多藝術家想象中的戴森球。 很難去想象這些東西 究竟有多龐大， 但你可以這么想。 地球——月球間的距離 是四十萬公里。 這些巨型結構中的 最簡單的單元， 是 100 倍地月距離。 它們是龐然大物。 再想象，這樣一個建筑 圍繞著一顆恒星運動。 你可以看到這為什么 可以造成數(shù)據(jù)中異常 如此不對稱，不自然的負峰。 10:58 但是即使是 外星人的超級建筑， 也不能違反物理定律。 任何使用大量能量的東西 將會產(chǎn)生熱量， 但是我們沒有觀測到。 但這有可能只是非常簡單的， 他們把熱量釋放到了另一個方向， 沒有對著地球。 11:22 我個人最喜歡的 另一種可能性是 我們恰好目睹了 一場星球大戰(zhàn)， 一顆行星被災難性地 徹底摧毀了。 我承認， 這會產(chǎn)生很多塵埃， 然而我們沒有觀測到。 但是如果我們已經(jīng) 在用外星人來解釋， 那誰說他們不會秋風掃落葉 一般清理干凈塵埃， 回收利用？ 11:50 你看，這很快 就激發(fā)想象力啦。 11:55 好啦，故事就是這樣。 我們的處境是， 既可以解釋成 我們沒搞清楚的自然現(xiàn)象， 又可以解釋成 我們沒搞清楚的外星人科技。 作為科學家，我個人 還是會賭這是個自然現(xiàn)象。 但是別誤解了，我絕對認同 能找到外星人非常棒。 不管怎樣，有新東西， 非常有趣的東西等待發(fā)現(xiàn)。 12:23 那么，接下來呢？ 我們需要繼續(xù)觀測這顆恒星 去更詳細地了解發(fā)生了什么。 然而，像我這樣的職業(yè)天文學家， 我們在這方面的資源有限。 而開普勒望遠鏡已經(jīng)在 執(zhí)行另一項計劃了。 所以我很高興地說，又一次， 12:43 公民科學家加入進來救場。 你看，這次， 業(yè)余天文愛好者 拿著他們的業(yè)余望遠鏡 立刻加入進來， 開始在自己的觀測點 夜觀此星。 我非常期待他們的發(fā)現(xiàn)。 對我來說，激動人心的是 這顆恒星可能根本不會被電腦發(fā)現(xiàn)， 13:07 因為我們單純沒有把 這樣的恒星當成目標。 更激動人心的是， 將來還有更多的數(shù)據(jù)。 有新的觀測項目要上馬， 準備觀測百萬顆恒星， 布滿全天。 思考一下：如果我們又找到 一顆這樣的恒星，意味著什么？ 13:32 而如果我們一顆都沒找到， 那又意味著什么？ 謝謝。 |
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