Look at an image of the Milky Way galaxy, and you cant help but notice its exquisite spiral arms. For nearly 100 years, astronomers have tried to understand how the Milky Way and other spiral galaxies formed these dramatic patterns--and now they think they finally have the answer.  

看看银河系的图片，你自然会注意到那漂亮的旋臂。近一百年来，天文学家们一直想搞清，银河系和其他旋涡星系的漂亮形状是怎样形成的。现在他们认为，终于找到答案了。

Current thinking about how spiral galaxies form trac es back to an idea nearly 2 millennia old, to 2nd-century Egyptian mathematician Ptolemy. Trying to describe how the five planets in the night sky followed seemingly irregular paths, Ptolemy hit upon an idea he called epicycles . Basically, the theory posits that, as an object orbits, it performs little loops that make it appear to wobble. The idea was revived in the 1920s to explain similar irregular movements among the stars in the Milky Way and later still to describe the formation of galactic spiral arms. But there have been little data to support it.

有关漩涡星系形成的公认观念可以追溯到近2,000年以前、公元二世纪时埃及数学家托勒密提出的一个观点。当设法解释夜空中的五颗行星为何好象沿着不规则的轨道运行时，托勒密脑海中闪现出一个观念，他称之为“本轮”。从根本上来讲，本轮理论做出了一个这样的假定：当一个物体做环绕运行的时候，它本身也会做小的环状运动，使其显得摇摆不定。在二十世纪二十年代的时候，这个观点又流行起来，用来解释银河系恒星之间类似的不规则运动。后来，该观点仍然用来解释星系旋臂的形成。但是，一直没有资料可以证实这个观点。

Independent mathematician Charles Francis of Hastings, U.K., had been studying a cosmological problem that required him to analyze the motions of stars. So he compiled data on more than 20,000 stars from existing sky surveys whose position in our galaxy and orbital velocity had been accurately measured. Among the data, he noticed something that startled him: Nothing supported the epicycle hypothesis. So Francis and independent astronomer Erik Anderson of Ashland, Oregon, developed a simulation based on the velocity distribution of stars that they found in the sky-survey data. As the two report online today in the Proceedings of the Royal Society A, when they ran the simulation, it quickly--within a hypothetical 300 million years--formed spiral arms similar to those in the Milky Way. The stars simply followed the laws of gravitation, as set down by Isaac Newton over 300 years ago. The idea was so sufficiently simple, Francis says, "that I had rejected it before because I thought that if it were right, it would already be known. In fact, it worked straightaway, giving a perfect fit with the data."

英国黑斯廷斯市搞独立研究的数学家查尔斯·弗朗西斯曾经一直研究一个宇宙学问题，该问题需要他对恒星的运动进行分析。这样，他从现有的天空观测资料中搜集到20,000多颗恒星的资料。这些恒星都位于我们银河系，对它们的轨道速度已经有过精确地测量。在这些数据资料中，他注意到一个令人吃惊的情况：这些数据资料都不支持本论说。因此，弗朗西斯和俄勒冈州阿什兰市搞独立研究的天文学家埃里克·安德森一起设计了一次模拟，该模拟以天空观测资料中的恒星速度分布为基础。今天，两位科学家在《皇家学会学报A》在线版上报道：进行模拟时发现，很快——大概在三亿年之内——就形成了类似银河系的旋臂。这些恒星完全符合三百多年前艾萨克·牛顿提出引力定律。弗朗西斯称：“道理十分简单。但我以前不接受这个观点，因为我认为如果符合引力定律的话，人们早就知道了。事实上，引力定律是直接起作用的，跟那些数据资料完全吻合。”

As Francis describes it, the Milky Way and other spiral galaxies operate like a giant, spiral-grooved funnel into which billions of marbles are pouring. The grooves represent the gravitational field of the galaxys spiral arms. Each marble finds a groove at the top of the funnel and begins to follow it down a never-ending slope, picking up momentum as it goes. Eventually, the marble gains enough momentum to jump free of its groove. It crosses to the next-highest one then falls back to a higher point in its original groove. (Watch the process here .)

根据弗朗西斯的描述，银河系和其他漩涡星系运行起来就象一个巨大的、带有螺旋形凹槽的漏斗，漏斗中正在注入几十亿个弹子。凹槽代表星系旋臂的引力场，每一个弹子在漏斗的顶端都会找到相应的凹槽，然后沿着凹槽、顺着一条永无休止的坡道运行下去，运行之中动力也在不断增加。最终，弹子的动力十足，跳离凹槽，串到一条相邻的较高凹槽中，然后又落回到原凹槽的一个更高的位置。

Astronomer Rainer Klement of the Max Planck Institute for Astronomy in Heidelberg, Germany, says the paper "comes up with an elegant way of explaining the velocity distribution we observe in the solar neighborhood." He says new space missions scheduled in the coming years should map the position and motions of more stars "with unprecedented precision," and he predicts that the new data will support the papers conclusions.

德国海森堡市马普学会天文分会的天文学家雷纳·克莱门特说：“该论文提出了一个极好的办法，解释了我们所观察的恒星附近的速度分布情况。”他表示：在未来几年中所计划的新一轮太空航天行动，应该能够“以前所未有的精确度”描绘出更多恒星的位置和运动情况。此外，克莱门特预测，新的数据资料将会支持该论文的结论。