Right Again, Einstein

As if his reputation needed cementing, astronomers have confirmed Albert Einstein's status as a supergenius once more. Studying a unique pair of pulsars--small and extremely dense leftovers from supernova explosions--researchers have measured an effect that was predicted by Einstein's 92-year-old general theory of relativity. The result, they report tomorrow in Science, is almost exactly what the famous physicist had foreseen.

In Einstein's relativistic universe, matter curves space and slows down time, and the speed of light remains the only constant. But those are the big effects. The theory of relativity also includes some more esoteric details, one of which is called spin precession. The idea goes like this: Two massive bodies orbiting near each other will warp space enough to disturb the central axis around which both are moving, causing them to begin wobbling just like spinning tops. Strong gravity creates this so-called precession, and the more massive the objects, the easier the precession is to observe.

It's not an easy theory to test. Researchers need two very dense objects orbiting very close together, and they have to be able to detect what is going on between them. Black holes are dense, but their event horizons preclude observations. The lack of candidates and telescopic power had frustrated astronomers for years, until the discovery in 2003 of a particular pair of pulsars. These asteroid-sized objects pack sunlike masses, extremely small orbits, and incredibly fast spins. They also emit powerful and ultraregular radio signals that are easily detectable with Earth-based dishes. Most important in this case, one pulsar eclipses the other briefly every couple of hours. That's key to detecting precession, because during each eclipse astronomers can determine the precise angle of the radio signal and therefore the pulsar's wobble over time.

For the past 4 years, an international team has been carefully tracking the signals of one of the pulsars and monitoring the signals' direction during eclipses--a observational technique "that has never been employed before," says astrophysicist and co-author Rene Breton of McGill University in Montreal, Canada. The researchers determined that the precession of the pulsar's orbital axis advances by 4.77 degrees per year, plus or minus 0.66 degrees. Calculations based on Einstein's theory predicted it should advance by 5.07 degrees per year, well within the margin of error.

"It's bang-on," says astrophysicist and Nobel laureate Joseph Taylor of Princeton University. "Einstein's theory passed the test this time," agrees astrophysicist Fotis Gavriil of NASA's Goddard Space Flight Center in Greenbelt, Maryland, who praises the study's "amazing high-precision measurement." So is Einstein's reputation secure? Says Gavriil, "Only with experiments like this will we know for sure."

正当人们快要淡忘他时，天文学家们再一次证实了阿尔波特·爱因斯坦的天才地位。研究者们对一对脉冲星--来自超新星爆炸后产生的小但密度极高的星体--的测量结果让爱因斯坦提出长达九十二年之久的广义相对论得到了证实。这个结果明天将被他们发表在《科学》杂志上，而那位著名的物理学家在生前几乎完全准确的对该结果做出预言。

在爱因斯坦的相对宇宙中，物质扭曲空间，令时间变慢，光速也不过是个常数。但这些都是宏观效应。相对论还包括一些更加深奥的细节，其中的一个被称作自转进动。该理论认为：两个距离较近的大质量物体彼此扭曲附近的空间，足以对它们运行的轨道中轴造成干扰，使它们像旋转的陀螺那样发生抖动。强大的引力制造了这个所谓的进动，质量越大的物体，它的进动越容易被观察到。

这不是一个容易被证实的理论。研究者们需要两个密度极高的物体，并让它们的轨道闭合在一起，此外研究者还要有能力对它们进行观测。黑洞密度足够高，但是他们的视界阻止了观察者。多年来，天文学家们受制于缺少合适的目标，以及望远镜力有不棣，直到2003年发现了一对特殊的脉冲星。这类星体只有小行星级别的体积，但有恒星级别的质量，极小的轨道，以及快得令人难以置信的自转速度。它们还会发射强烈的红外辐射，这让地球上的探测设备更容易观察它们。更重要的是，每隔几个小时，其中的一颗脉冲星会遮挡另外一颗。这是探测进动的关键，因为在每次遮挡期间天文学家们可以确定放射线信号的精确角度，并因此断定脉冲星的抖动时间。

在整整四年时间里，一个国际团队一直仔细的跟踪其中一颗脉冲星的信号，并在遮挡期间监视信号的方向--该观察技术"此前从未被使用过"，加拿大蒙特利尔市麦克吉尔大学天体物理学家以及合作者Rene Breton说。研究者确定，脉冲星的轨道轴进动幅度每年前进4.77度，误差0.66度。基于爱因斯坦理论做出的计算，每年前进5.07度，在误差范围之内。

"结果完全吻合"，普林斯顿大学诺贝尔得主，天体物理学家Joseph Taylor认为。"爱因斯坦的理论通过了这次考验"，马里兰州NASA的宇航中心天体物理学家Fotis Gavriil也如此表示。他盛赞该项研究"精确得令人惊讶"。这个结果会巩固爱因斯坦的地位吗？Gavriil表示，"只有这样的实验才能得到我们的肯定"。
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