For decades, astronomers have known about irregular outbursts from the double star system V745 Sco, which is located about 25,000 light years from Earth. V745 Sco is a binary star system that consists of a red giant star and a white dwarf locked together by gravity. These two stellar objects orbit so closely around one another that the outer layers of the red giant are pulled away by the intense gravitational force of the white dwarf. This material gradually falls onto the surface of the white dwarf. Over time, enough material may accumulate on the white dwarf to trigger a colossal thermonuclear explosion, causing a dramatic brightening of the binary called a nova. Astronomers saw V745 Sco fade by a factor of a thousand in optical light over the course of about 9 days.

In 2014, astronomers finally got their chance to see the phenomena, using the Chandra X-Ray Observatory. Their key finding was it appeared that most of the material ejected by the explosion was moving towards us and developed a 3-D computer model of the explosion that explained the observations. In this model they included a large disk of cool gas around the equator of the binary caused by the white dwarf pulling on a wind of gas streaming away from the red giant.

In the figure showing the new 3-D model of the explosion, the blast wave is yellow, the mass ejected by the explosion is purple, and the disk of cooler material, which is mostly untouched by the effects of the blast wave, is blue. An extraordinary amount of energy was released during the explosion, equivalent to about 10 million trillion hydrogen bombs.

Image Credit: NASA/CXC/M.Weiss

几十年来,天文学家们已经知道了距离地球25000光年的双星系统V745 Sco的不规则爆发。V745 Sco是一个双星系统,由一颗红巨星和一颗白矮星通过引力锁定在一起。这两个恒星物体如此紧密地围绕着对方运行,以至于红巨星的外层被白矮星的强大引力拉走了。这些物质逐渐落到白矮星的表面。随着时间的推移,白矮星上可能积累了足够多的物质,从而引发巨大的热核爆炸,导致被称为新星的双星出现引人注目的亮化。天文学家们发现V745 Sco在大约9天的时间里,可见光减弱了1000倍。

2014年,天文学家终于有机会利用钱德拉X射线天文台观测到这一现象。他们的关键发现是,爆炸喷出的大部分物质似乎正向我们移动,并开发了一个爆炸的三维计算机模型来解释观测结果。在这个模型中,他们包括了围绕在双星赤道附近的一个巨大的冷气体盘,这是由白矮星拉着一股从红巨星流走的气体风造成的。

在这张显示爆炸新三维模型的图中,爆炸波是黄色的,爆炸喷出的物质是紫色的,而大部分未受爆炸波影响的较冷的物质盘是蓝色的。爆炸释放了大量的能量,相当于1000万亿个氢弹。

影像来源:NASA/CXC/M.Weiss

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忠洋 张

将观测爆发的x射线以可见光图片的形式展现在我面前,实在是奇特。