大众科学：世界最大望远镜对准地心

“冰立方”望远镜的一串数字光模块被送入冰下（美国《大众科学》网站）

One of IceCube's Digital Optical Modules NSF/University of Wisconsin

    (草根博览综合讯)美国《大众科学》月刊网站6月25日文章报道，在南极冰层1英里处建造世界上最大的望远镜（作者劳里·席密特）

    想象一个高度超过纽约帝国大厦、芝加哥西尔斯大楼和上海环球金融中心高度总和的望远镜阵列。这就是天文学家们正在南极冰层下1英里处组装的东西。但这部望远镜并没有对准天空，而是指向地球中心。

    由美国国家科学基金会出资、美国威斯康星大学研发的“冰立方”望远镜将搜寻在宇宙最猛烈的巨变中产生的中微子。这些巨变包括伽马射线爆发、超新星爆炸以及与黑洞有关的其他事件。中微子可能是了解自然界能量最高的粒子的起源及其物理过程的关键。

    中微子是不带电的中性亚原子粒子，是核反应过程中中子转变成质子时发射出来的。它们从中微子源中发出，直线运动，速度接近于光速，并且非常小，几乎可以不受干扰地穿过固体物质。然而，正是这个特性使其极难被发现，有宇宙站的“隐身者”之称。

    “冰立方”望远镜正在冰下建造，要安装几千个叫做数字光模块的球形传感器。这些数字光模块每60个一串，利用热水钻将其嵌入4700英尺至8000英尺深处冰融化形成的洞中。尽管研究小组可以通过向传感器发送电子信号来进行调节操作，但一旦这些传感器被安装到冰内就不可能对它们进行维护。

    科学家们认为，散播在我们周围的大多数中微子是在大约150亿年前产生的，即在宇宙诞生后不久。他们还提出理论说，如今存在这么多中微子，以致它们构成了据信是宇宙大爆炸“余辉”的宇宙背景辐射。核电站、粒子加速器、核弹、普通大气现象和超新星爆炸也会产生新的中微子。

    “冰立方”望远镜可能成为搜寻宇宙暗物质的有力工具。人们认为暗物质是存在的，理由是它对可见物质有引力作用。天文学家们提出理论说，暗物质占宇宙物质的80%。

    进入：《参考消息》奖学金·国际知识竞赛开始（含公告）

          《参考消息》奖学金·国际知识竞赛试题（一）及答案

原文：

Imagine a telescope array that exceeds the height of the Empire State Building, the Chicago Sears Tower, and Shanghai's World Financial Center combined. That's what astronomers are piecing together about a mile beneath the ice at the South Pole. But this telescope isn't aimed at the sky -- it points to the center of the Earth.

The IceCube telescope, developed at the University of Wisconsin with funding from the National Science Foundation, will search for neutrinos generated by the most violent cataclysms in the universe, such as gamma ray bursts, supernova explosions, and other events involving black holes. The neutrinos could hold the key to understanding the origin and physical processes of the highest energy particles in nature.

Neutrinos are neutrally charged subatomic particles that are emitted when neutrons transform into protons in nuclear reactions. They travel at close to the speed of light in straight lines from their source and are so small they can pass through solid matter almost undisturbed. But this same trait makes them extremely difficult to detect. Scientists have been looking at doing astronomy studies using neutrinos since the 1950s, but the challenge has been the technology needed to build a a sufficiently sized observatory -- detectors must be very large to detect a significant number of neutrinos.

IceCube is being engineered under the ice by deploying thousands of spherical sensors called Digital Optical Modules (DOMs). Using a hot water drill, the DOMs are inserted into holes melted into the ice on "strings" of 60 modules each at depths of 4,700-8,000 feet. It takes about 11 hours to deploy one string of 60 DOMs, with about 200,000 gallons of ice being melted for each hole drilled. IceCube detects the blue light from the nuclear reaction initiated by the direct strike of a neutrino on an atom of ice, and each DOM will have a computer that relays digital data to the surface.

Building the IceCube telescope under the Antarctic ice will protect the detector from cosmic rays and other background radiation. Once the detectors are frozen in the ice, they will remain there for about 25,000 years -- the estimated time it will take for that section of the ice to migrate to the Antarctic coast. Although the research team can tweak operations by sending electronic signals to the sensors, no maintenance is possible once they are deployed in the ice.

Scientists believe that most of the neutrinos floating around originated about 15 billion years ago, shortly after the birth of the universe. They also theorize that there are now so many neutrinos that they constitute a cosmic background radiation, believed to be the "afterglow" of the Big Bang. New neutrinos are also being produced from nuclear power stations, particle accelerators, nuclear bombs, general atmospheric phenomena, and supernova explosions.

IceCube could be a powerful tool to search for dark matter in the universe -- matter that is presumed to exist based on its gravitational effects on visible matter. Astronomers theorize that dark matter makes up 80 percent of matter in the universe.

This week, EE Times interviewed Albrecht Karle, a Wisconsin physics professor who is working on the project.

The telescope array is about 95 percent constructed, with completion scheduled for 2011 at a total cost of $271 million.

（原文：http://www.popsci.com/technology/article/2010-06/building-worlds-largest-telescope-mile-under-antarctic-ice）

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