NASA 美国宇航局的每日一图 3月份
发布: 2009-1-14 17:53 | 作者: webmaster | 来源: 本站原创 | 查看: 156次
2008 March 28 
Credit: NASA Swift Team, Stefan Immler (GSFC) et al.
说明: 到底我们能够看多远呢? 即使是最远的 肉眼可以看到的星星也只有距离我们仅仅数百或数千光年，也只在本银河系内。 当然，如果你知道仙女座星系 (Andr omeda Galaxy)在夜空中的位置，那团淡淡模糊的云气，距离我们两百五十万光年远。 但是在三月十九日朝向北天星座牧夫座(Bootes)的方向，即使不用 双筒或是望远镜，你仍然能够见证到 一个弱的，很短暂的闪光，来自于宇宙中的伽玛射线爆发(Gamma-ray burst)。 爆发的来源被距离我们约有七十五亿光年，大约位于宇宙的大小一半的位置。 目前这是用裸视所能看到最远的星体，伽玛射线爆发的亮度约有最亮的超新星爆炸的两百五十万倍，这个伽玛射线爆发被史威夫特卫星(Swift satellite)确认及定位，它能够最快测量距离，以及通知地面的望远镜观测。 编号为GRB080319B伽玛射线爆发的余晖，上面这两幅影像，分别是左边的X射线波段以及右边的紫外线波段影像。
Explanation: How far can you see? Even the faintest stars visible to the eye are merely hundreds or thousands of light-years distant, all well within our own Milky Way Galaxy. Of course, if you know where to look you can also spot the Andromeda Galaxy as a pale, fuzzy cloud, around 2.5 million light-years away. But staring toward the northern constellation Bootes on March 19th, even without binoculars or telescope you still could have witnessed a faint, brief, flash of light from a gamma-ray burst. The source of that burst has been discovered to lie over halfway across the Universe at a distance of about 7.5 billion light-years. Now holding the distinction of the most distant object that could be seen by the unaided eye and the intrinsically brightest object ever detected, the cosmic explosion is estimated to have been over 2.5 million times more luminous than the brightest known supernova. The monster burst was identified and located by the orbiting Swift satellite, enabling rapid distance measurements and follow-up observations by large ground-based telescopes. The fading afterglow of the gamma-ray burster, cataloged as GRB080319B, is shown in thesetwo panels in X-rays (left) and ultraviolet light (right).
Explanation: How far can you see? Even the faintest stars visible to the eye are merely hundreds or thousands of light-years distant, all well within our own Milky Way Galaxy. Of course, if you know where to look you can also spot the Andromeda Galaxy as a pale, fuzzy cloud, around 2.5 million light-years away. But staring toward the northern constellation Bootes on March 19th, even without binoculars or telescope you still could have witnessed a faint, brief, flash of light from a gamma-ray burst. The source of that burst has been discovered to lie over halfway across the Universe at a distance of about 7.5 billion light-years. Now holding the distinction of the most distant object that could be seen by the unaided eye and the intrinsically brightest object ever detected, the cosmic explosion is estimated to have been over 2.5 million times more luminous than the brightest known supernova. The monster burst was identified and located by the orbiting Swift satellite, enabling rapid distance measurements and follow-up observations by large ground-based telescopes. The fading afterglow of the gamma-ray burster, cataloged as GRB080319B, is shown in thesetwo panels in X-rays (left) and ultraviolet light (right).
