Particle Astrophysics with the Milagro and STACEE Telescopes

在目前天文学的“黄金时代”出现的惊人结果中，有一些涉及甚高伽马射线望远镜。 这些探测器探测到的光包能量比普通室内光大数万亿倍。 宇宙中有什么物体能发出这样的信息包呢？ 天体物理学家认为，在大型星系中心附近加速到极高速度的普通粒子，或者由落入中心大型黑洞的物质发射出来的粒子，可能是罪魁祸首。 也有巨大的，短暂的伽马射线爆发来自天空中半随机的地方，被认为是来自一些特别大的遥远的超新星（hypernova）或黑洞与星星合并。 只有少数特殊的望远镜才能“看到”这些伽马射线，其中两台望远镜是由美国国家科学基金会资助的加州大学圣克鲁斯小组赞助的，这两台望远镜是Milagro和STACEE，都位于新墨西哥州。 伽马射线是如此难以捉摸，没有太空望远镜可以探测到它们，一个大型的地面设备是必要的。 米拉格罗没有使用玻璃透镜（伽马射线不会聚焦），而是使用一个600万加仑的特别纯净的水水库，将单个伽马射线产生的粒子雨转换为普通能量的紫外线。 这些光到达水中的光电探测器的时间被用来创建伽马射线天空的图像。 Milagro在所有天气下日夜工作，并同时在可见天空中的任何地方“点”。 在最初的几年里，它取得了足够的成功，NSF提供资金通过增加外围水箱来大幅扩大它，每个水箱都提高了它的指向能力和对遥远来源的敏感性。 相比之下，STACEE是一个夜间望远镜，带有镜子将光线引导到中央摄像头。 它可以看到大气中产生的蓝色和紫外线，这些光线来自米拉格罗使用的相同类型的淋浴，但对较低能量范围的伽马射线敏感（仅为普通光线能量的500亿倍！）。 日落后，天空晴朗时，STACEE使用了桑迪亚实验室的太阳能收集器的镜子。 这两台望远镜在研究这些壮观的源时是互补的。本项目的目标是完善这两台望远镜，并有助于更好地了解银河系中心、黑洞和超新星等引擎如何真正创造出高能粒子。 即使伽马射线爆发涉及最高能量还是局限于较低的范围，我们也还不知道。 到目前为止，米拉格罗的一个事件是能量在“万亿倍”范围内的唯一证据。和科学界的惯例一样，这一重大发现可能是研究人员甚至没有预料到的：还没有人证实斯蒂芬·霍金1974年关于小黑洞爆炸蒸发的开创性预测，但米拉格罗可以做到这一点，如果一个足够接近的话。 因此，沿着这些基本项目和仅仅是壮观的发现，真正非凡的发现需要研究人员的想象力和奉献精神。这些研究人员齐心协力，向纳税的公众和他们的学生--下一代天体物理学家--传达搜索的兴奋和他们的发现。

Among the amazing results emerging from the present "Golden Age" of astronomy are those involving Very High Gamma-ray telescopes. These detect light packets of energies trillions of times larger than ordinary room light. What objects in the cosmos can emit such packets? Astrophysicists believe that ordinary particles accelerated to tremendous speeds near the centers of large galaxies, or emitted by material falling into large black holes at the centers, are likely responsible. There are also huge, short bursts of gamma rays from semi-random places in the sky, thought to be from some especially large far-away supernova (hypernova) or a black hole merger with a star. Only a few special telescopes can "see" these gamma rays, and two of them are sponsored in part by the UC Santa Cruz group funded by this NSF project.The two telescopes are Milagro and STACEE, both located in New Mexico. The gamma rays are so elusive that no space telescope can detect them, and a large ground-based device is necessary. Milagro uses no glass lenses (the gamma-ray light would not focus), but uses instead a 6 million gallon reservoir of specially pure water to convert a shower of particles produced by a single gamma ray into ultraviolet light of ordinary energies. The arrival time of that light on photodetectors in the water is then used to create an image of the gamma-ray sky. Milagro works day and night in all weather and "points" everywhere in the visible sky simultaneously. In its first few years, it was successful enough that the NSF provided funds to enlarge it substantially by the addition of outlying water tanks, each of which improves its pointing ability and sensitivity to far-away sources. By contrast, STACEE is a nighttime telescope with mirrors to direct light to a central camera. It sees blue and ultraviolet light produced in the atmosphere from those same type of showers used by Milagro, but is sensitive down to a lower range of energies of gamma-ray (only 50 billion times the energy of ordinary light!). STACEE uses the mirrors of a solar energy collector belonging to Sandia Laboratories, after sunset when the skies are clear. The two telescopes are complementary to one another in the study of these spectacular sources.The goal of this Project is to perfect these two telescopes and to contribute to a better understanding of how the engines-galactic centers, black holes and hypernovae-really create the high-energy particles. It is not yet known even if the bursts of gamma-rays involve the highest energies or if they are confined to a lower range. Thus far, one event from Milagro is the only evidence for energies of the "trillion-times" range.As usual with science, the big discovery may be one the researchers don't even expect: no one has yet confirmed the 1974 groundbreaking predictions of Stephen Hawking concerning the explosive evaporation of small black holes, but Milagro could do this if one were close enough. So along with the bread-and-butter projects and the merely spectacular, the truly extraordinary discovery holds the imagination and dedication of the researchers.Those same researchers make a concerted effort to communicate the excitement of the search and their discoveries to the taxpaying public and to their students-the next generation of astrophysicists.