超大質量黑洞或將碰撞 35億光年外星系面臨毀滅
The apocalypse is still on, apparently — at least in a galaxy about 3.5 billion light-years from here.
看起來，末日仍然會上演——至少是在距離我們35億光年的一個星系。
Last winter a team of Caltech astronomers reported that a pair of supermassive black holes appeared to be spiraling together toward a cataclysmic collision that could bring down the curtains in that galaxy.
過去的這個冬天，加州理工的一羣天文學家發佈論文稱，一對超大質量黑洞似乎在朝着災難性碰撞的軌跡運行，而這種碰撞可能會宣告該星系的落幕。
The evidence was a rhythmic flickering from the galaxy’s nucleus, a quasar known as PG 1302-102, which Matthew Graham and his colleagues interpreted as the fatal mating dance of a pair of black holes with a total mass of more than a billion suns. Their merger, the astronomers calculated, could release as much energy as 100 million supernova explosions, mostly in the form of violent ripples in space-time known as gravitational waves that would blow the stars out of that hapless galaxy like leaves off a roof.
他們的證據是這一星系中心的類星體PG 1302-102表現出了一種有規律的閃動。研究人員馬修·格雷厄姆(Matthew Graham)及其同事認爲，這代表了一對總質量超過太陽10億倍的黑洞在互相環繞，走向死亡。根據他們的估算，二者合併或許可以釋放出1億顆超新星爆炸的能量，多數表現爲“引力波”。這種時空中的猛烈漣漪會讓星體從那倒黴的星系中噴出，好比是從屋頂上颳走樹葉。
Now a new analysis of the system by Daniel D’Orazio of Columbia University and his colleagues has added weight to that conclusion. Mr. D’Orazio, a graduate student, and his colleagues Zoltan Haiman and David Schiminovich propose that most of the light from the quasar is coming from a massive disc of gas surrounding the smaller of the two black holes.
現在，哥倫比亞大學(Columbia University)的丹尼爾·德奧拉齊奧(Daniel D’Orazio)及其同事對這一星系進行的新分析，給上述結論增添了份量。研究生德奧拉齊奧和同事佐爾坦·海曼(Zoltan Haiman)、戴維·希米諾維奇(David Schiminovich)提出，這顆類星體發出的光多數來自圍繞着其中一個較小黑洞的碩大的吸積盤。
As the black holes and their attendant discs swing around each other at high speeds, the light from the disk that is coming toward us gets a boost from relativistic effects – a so-called Doppler boost — the same way a siren gets louder and more high-pitched as it approaches, giving rise to a periodic increase in brightness every five years.
這兩個黑洞及其吸積盤相互高速旋轉時，來自這個吸積盤的光線在對着地球的方向會因相對運動產生的多普勒效應而加強——好比對面駛來的火車鳴笛聲會變得更大聲、更尖細一樣——令它每隔五年會週期性地增大亮度。
The Columbia astronomers’ model predicts that the variation would be two or three times greater in ultraviolet light than in visible light. And that is exactly what they found when they compared archival data from the Hubble Space Telescope and NASA’s Galex space telescope to the visible-light data previously analyzed by Dr. Graham’s group.
哥倫比亞大學的這三名天文學家建立的模型預測，其中紫外線的變化會比可見光顯著。他們拿出哈勃太空望遠鏡和美國航空航天局的星系演化探測器(Galex)的歷史數據，與格雷厄姆團隊之前分析的可見光數據進行比對，發現結果正好與預測吻合。
“What’s big is that the Doppler boost is inevitable,” Dr. Haiman said in an email. Given reasonable assumptions about the masses of the two black holes, their model predicts the right ultraviolet data. “This is rare in ‘messy’ astronomy,” he said, “to have an indisputable clean effect, which explains the data.” Follow-up observations of ultraviolet and visible light emissions in the coming years could help the clinch the case, the authors said. Their paper was published on Wednesday in the journal Nature.
“其中的重大意義在於，這隻能是多普勒效應，”海曼博士通過電子郵件接受採訪時表示。只要給出有關這兩個黑洞質量的合理假設，他們的模型就能預測出準確的紫外線數據。“在‘混亂’的天文學研究中，很難看到有一個毫無爭議的清晰理論能夠對數據做出解釋，”他說。三名研究人員表示，未來幾年對紫外線和可見光輻射的追蹤觀察或將有利於得出確鑿的結論。他們的論文於本週三發表在《自然》雜誌(Nature)上。
Their model suggests that the black holes are orbiting each other at a distance of some 200 billion miles, less than a tenth of a light-year, a cosmic whisker. At that distance the black holes would be rapidly losing energy by radiating gravitational waves and could spiral together into the final bang in as little as 100,000 years, Dr. Haiman said, depending on their relative masses.
他們的模型顯示，兩個黑洞在相互環繞，之間的距離約爲2000億英里，不到0.1光年。這在宇宙中可謂緊密相連。海曼稱，相距這麼近的話，這兩個黑洞應當以發出引力波的形式快速喪失能量，並且可能會最快在10萬年後最終相撞。
“Basically, the more massive the holes, the faster gravitational waves drive them together, and we do require them to be as massive as allowed to be,” he said in an email. For their model to hold up, the larger of the black holes has to be a billion solar masses or more.
“基本上，雙黑洞質量越大，引力波將他們拉到一起的速度越快，而我們的研究的確假定他們在允許的範圍內質量儘可能地大，”他在郵件中寫道。他們的模型要想成立，雙黑洞中較大的那個的質量至少得相當於10億個太陽。
E. Sterl Phinney, a Caltech astronomer and expert on supermassive black holes currently on sabbatical at Radboud University in the Netherlands, agreed that Dr. Haiman’s model explains the quasar variations. “So Occam’s razor makes it attractive,” he said in an email, referring to the long-held principle that physicists should adopt the simplest theory that fits the facts.
加州理工的天文學家E·施特爾·菲尼(E. Sterl Phinney)是超大質量黑洞領域的專家，目前在荷蘭的內梅亨大學(Radboud University)休學術假。他認爲海曼的模型能夠解釋這顆類星體的閃動。“奧卡姆剃刀讓它討人喜歡起來，”他在接受採訪的電子郵件中寫道。奧卡姆剃刀是一個由來已久的原則，認爲物理學家們應該採用最簡潔的理論來解釋事實。
But it was surprising, he said, to find a pair of supermassive black holes that have gotten so close.
不過他也表示，找到距離如此相近的一對超大質量黑洞令人意外。
Black holes, predicted by Albert Einstein’s general theory of relativity, the prevailing theory of gravity, are objects so dense that not even light can escape from them. In effect they are bottomless pits in space-time. Every galaxy of note seems to have a supermassive black hole, weighing millions or billions of times as much as the sun, burping sparks of half-eaten stars and gas.
阿爾伯特·愛因斯坦(Albert Einstein)的廣義相對論是有關引力的權威理論，其中預測了黑洞的存在。黑洞十分緻密，以致於光線都無法從中逃脫。它們實際上是時空中的無底洞。每個重要星系似乎都有一個質量爲太陽無數倍的超大黑洞，不斷輻射出正被吞噬的星體和氣體的閃爍光線。
When galaxies merge, their resident black holes are sent into forced marriages, orbiting each other. But without gravitational interactions with stars or interstellar gas, supermassive black holes can’t get close enough to each other to go into a rapid death spiral, a situation known as the “final parsec” problem. (A parsec is the astronomical standard of distance, 3.26 light-years.)
當星系合併的時候，各自的黑洞被迫拴在一起，相互環繞運動。不過，如果沒有與星體或星際氣體之間的相互牽引，超大質量黑洞不能靠近到能迅速走向碰撞的地步，而這種現象被稱爲“最後的秒差距”問題（秒差距是天文學距離單位，1秒差距等於3.26光年）。
So, as Dr. Phinney explained, unless hundreds of millions of solar masses of gas accompany the black holes, “there are not very convincing ways of getting them to smaller separations” like the black holes in PG 1302-102.
因此，正如菲尼解釋的那樣，除非雙黑洞周圍有數億太陽質量的氣體，“沒有令人信服的辦法來讓它們的距離縮小”到PG 1302-102的兩個黑洞那麼近的地步。
At least that is the theory. If such systems are common, Dr. Phinney said, the gravitational waves emanating from them should sweep the universe and disrupt the timing of signals from pulsars, an effect that could be detected within the next few years by various ongoing programs to time pulsars.
至少理論上如此。菲尼稱，假如這種系統很常見，那麼從中發出的引力波應該席捲整個宇宙，干擾到脈衝星信號的節奏，那麼在未來幾年裏，目前正在進行的多個觀測脈衝星時間的項目就應該可以觀察到這一現象。
“A scientific theory is only as good as the tests which it has passed,” Mr. D’Orazio said in an email. Although general relativity has passed all of the observational and experimental tests thrown at it so far, some of its predictions can only be tested in the most extreme gravitational environments, namely black holes. “Detection of gravitational waves,” he said, “is a direct probe of this region and hence the secrets of gravity.”
“科學理論的正確性是由它經受的考驗決定的，”德奧拉齊奧在郵件中表示。儘管廣義相對論經受住了迄今爲止所有與之相關的實驗和觀測的考驗，但該理論蘊含的一些預測只能在最極端的引力環境中檢驗，也就是黑洞。“觀測引力波是對這種區域的直接探究，繼而也是對引力的奧祕的直接探究，”他說。
