Astronomy Picture of the Day

Explanation: Cosmic Rays are celestial high energy particles traveling at nearly the speed of light, which constantly bombard the Earth. Discovered during high altitude balloon flights in 1912 their source has been a long standing mystery. But a recent theory suggests that cosmic ray particles are atomic nuclei blasted from dust grains formed in supernovae, the death explosions of massive stars. This artist's illustration shows a supernova explosion (at left) and a conical section of the expanding cloud of ejected material. Atoms are torn from the brownish bands of "dust" material by shock waves (represented by orange rings). The shocks in the expanding blast wave then accelerate the atoms to near light speeds firing them into interstellar space like cosmic bullets. The theory is supported by observations indicating that high velocity dust was formed in the nearby supernova 1987A, and that Beryllium, a light element created in Cosmic Ray collisions, is found equally in both old an young stars. NASA's Advanced Composition Explorer (ACE) satellite can also test details of the theory by directly measuring Cosmic Rays.

宇宙射線是源自天體、幾乎以光速飛行、並不斷轟擊地球的高能粒子。 它是在1912年發現於高空氣球上，然而其來源一直是個長期未解的謎。 但最近有一項理論指出，在大質量恆星發生死亡爆炸時，形成於其中的塵埃微粒受到轟擊後，碎裂高速噴出的原子核即是宇宙射線。 這幅藝術家所繪的圖示，呈現一例超新星爆炸（左邊）和一團不斷擴張的噴濺物質雲之錐狀剖面。 其中，原子被震波（以橙色環代表）從褐色的 "塵埃 "物質帶撕裂噴濺出來。 擴張爆炸波中的震波然後將原子加速到接近光速，把它們像宇宙子彈一樣射入星際空間。 這項獲得觀察支持的理論，顯示鄰近的1987A超新星曾產生高速移動的塵埃，而鈹這種可形成於宇宙射線碰撞的輕元素，在老恒星和年輕恒星皆可找到。 美國航太總署的宇宙成分先進探測衛星（ACE），可經由直接量測宇宙射線，來測試此理論的細節。