Take any square kilometer of Earth’s surface. About once a year an extraordinary event occurs in the sky directly above that patch of land or sea: the hefty nucleus of a heavy element slams into the top of Earth’s atmosphere at close to the speed of light.

Scientists have been unable to tell where these particles come from, in part because their trajectories can be nudged by galactic magnetic fields. Another puzzle is how the particles reach such blistering speeds.

Two theories dominate attempts to explain these mysteries. One posits that the particles mostly come from exploding stars and other high-energy phenomena in our galaxy. The other speculates that the particles are produced beyond our galaxy—perhaps in the active cores of other galaxies surrounding the Milky Way. Now a study in the journal Science supports that second notion. [Link to come]

Amazingly, any of these “ultra-high-energy cosmic rays” has the kinetic energy of an apple falling from a tree to the ground. That means that Isaac Newton, or you, would definitely feel it hit your head.

Luckily, that never happens. Instead, when these cosmic speed demons strike our atmosphere they create a brief flash of light, as well as high-altitude “air showers” of less-energetic particles that harmlessly dissipate.

In the new study, an international team of more than 400 researchers analyzed a dozen years’ worth of these events. They used the Pierre Auger Observatory, a Rhode-Island-sized array of telescopes and 1,600 particle detectors operating in western Argentina, to record air showers from more than 30,000 ultrahigh-energy cosmic rays. And it turns out that most of the particles appear to come from a broad, relatively galaxy-rich region of sky located about 90 degrees away from the Milky Way’s center. Which suggests that they arise in faraway galaxies perhaps from spinning supermassive black holes, rather than anywhere closer to home. What a long, strange trip they’ve made.

—Lee Billings

[The above text is a transcript of this podcast.]

中文翻译

占地面的任何平方公里。大约每年一次，在这片土地或海洋上方的天空中发生了一件非同寻常的事件：重元素的巨大核心以接近光速的速度猛烈撞击地球大气顶部。


科学家们无法分辨这些粒子来自何处，部分原因是它们的轨迹可以被银河磁场所推动。另一个难题是粒子如何达到如此高的速度。


两种理论主导着解释这些奥秘的尝试。有人认为这些粒子主要来自爆炸恒星和银河系中的其他高能现象。另一个推测粒子是在我们的银河系之外产生的 - 也许是在银河系周围其他星系的活跃核心。现在，科学期刊的一项研究支持第二个概念。 [链接来]


令人惊讶的是，这些“超高能宇宙射线”中的任何一种都具有苹果从树上落到地面的动能。这意味着艾萨克牛顿，或者你，肯定会感觉到它击中你的头。


幸运的是，这从未发生过。相反，当这些宇宙速度恶魔袭击我们的大气层时，它们会产生短暂的闪光，以及低能量粒子的高空“空气阵雨”，这些粒子无害地消散。


在这项新研究中，一个由400多名研究人员组成的国际团队分析了这些事件的十几年。他们使用皮埃尔奥格天文台，一个罗德岛大小的望远镜阵列和在阿根廷西部运行的1600个粒子探测器，记录超过30,000个超高能宇宙射线的空中阵雨。事实证明，大多数粒子似乎来自一个宽阔的，相对星系丰富的天空区域，距离银河系中心约90度。这表明它们出现在遥远的星系中，可能来自旋转的超大质量黑洞，而不是离家更近的地方。他们做了多么奇怪的旅行。


-Lee Billings