至今为止移动最快的恒星被NASA的钱德拉X射线天文台发现了。这个宇宙加农炮正在挑战解释其起泡速度的理论。
天文学家使用钱德拉观察了一颗中子星，是已知的RX J0822-4300，发现了5年之久。在这段期间，在钱德拉天文台3次观测中清楚的表明中子星离开了其中心的Puppis A超新星遗迹。这个遗迹是一个星形状区域，形成于同一个爆炸期间，中子星也是在那时形成，大体时间为3700年前。
通过综合性的分析于他到地球这个距离上在天空中移动的长度，天文学家断定中子星的移动速度为3000000英里每小时。以这个速度，RX J0822-430肯定已经逃逸银河数百万年之久，也旅行了大约20光年左右的路程。
这颗恒星每小时移动3000000英里，“但是由于距离太过遥远以至于我们在5年间的所看到的错觉运动的跨度比起从一个足球场长度的距离上看一辩士上数字词1的高度还小”佛蒙特州Middlebury学院的 Frank Winkler 说到。“这是值得注意的并且是一个真正意义上体现钱德拉的强大力量，就算极其微小的移动也能被测量出”
“就在刚出生后不久，这个中子星就得到了一张离开银河系的路票”来自NASA的Goddard宇宙发射中心的共著者 Robert Petre 说到“天文学家已经观测到其他恒星冲出银河系，但很少有他这么快的”
被叫做hypervelocity 的恒星在以前已经被发现以1000000英里的时速脱离银河系。一个存在于RX J0822-4300 和其他被报道的星系的最大不同是其起始的逃逸速度。hypervelocity恒星被认为是与星系中心巨大黑洞相互作用时被抛出的。
这个中子星，通过对比，是靠制造Puppis A的超新星抛出而获得运动的。数据表明爆炸是单向的，中子星的反冲力在一个方向，另外来自爆炸的琐屑在另一个方向。
超新星的形成是当大质量恒星核心爆裂时产生中子星的时候。计算机模拟表明恒星的外层的INFALL变成中子星时释放出巨大的能量。当这能量向外传播时，其能反转INFALL并以每小时数百万英里的速度喷发掉恒星的外层。由于气流的复杂性，喷射是不匀称的，就好比火箭效应，中子星的推进是在相反的方向。
“这个宇宙泡状球体的难迷惑就在于在自然条件下是如何弄出这么强有力的大炮”Winkler说到。高速可以被解释成由常见的高能量爆炸引起，但是模型非常复杂并很难适用于真正的爆炸。
One of the fastest moving stars ever seen has been discovered with NASA's Chandra X-ray Observatory. This cosmic cannonball is challenging theories to explain its blistering speed.
Astronomers used Chandra to observe a neutron star, known as RX J0822-4300, over a period of about five years. During that span, three Chandra observations clearly show the neutron star moving away from the center of the Puppis A supernova remnant. This remnant is the stellar debris field created during the same explosion in which the neutron star was formed about 3700 years ago.
By combining how far it has moved across the sky with its distance from Earth, astronomers determined the neutron star is moving at over 3 million miles per hour. At this rate, RX J0822-4300 is destined to escape from the Milky Way after millions of years, even though it has only traveled about 20 light years so far.
"This star is moving at 3 million miles an hour, but it's so far away that the apparent motion we see in five years is less than the height of the numerals in the date on a penny, seen from the length of a football field," said Frank Winkler of Middlebury College in Vermont. "It's remarkable, and a real testament to the power of Chandra, that such a tiny motion can be measured."
"Just after it was born, this neutron star got a one-way ticket out of the Galaxy," said co-author Robert Petre of NASA's Goddard Space Flight Center in Greenbelt, Md. "Astronomers have seen other stars being flung out of the Milky Way, but few as fast as this."
So-called hypervelocity stars have been previously discovered shooting out of the Milky Way with speeds around one million miles per hour. One key difference between RX J0822-4300 and these other reported galactic escapees is the source of their speed. The hypervelocity stars are thought to have been ejected by interactions with the supermassive black hole in the Galaxy's center.
This neutron star, by contrast, was flung into motion by the supernova that created Puppis A. The data suggest the explosion was lop-sided, kicking the neutron star in one direction and the debris from the explosion in the other.
The supernova was precipitated when the core of a massive star imploded to form a neutron star. Computer simulations show that the infall of the outer layers of the star onto a neutron star releases an enormous amount of energy. As this energy propagates outward, it can reverse the infall and eject the outer layers of the star at speeds of millions of miles per hour. Due to the complexity of the flow, the ejection is not symmetric, leading to a rocket effect that propels the neutron star in the opposite direction.
The breakneck speed of the Puppis A neutron star, plus an apparent lack of pulsations from it, is not easily explained by even the most sophisticated supernova explosion models.
"The puzzle about this cosmic cannonball is how nature can make such a powerful cannon," said Winkler. "The high speed might be explained by an unusually energetic explosion, but the models are complicated and hard to apply to real explosions."
自翻
URL：http://spacespin.org/article.php/71137-chandra-cosmic-cannonball
大图
复合图
可见光波段
X射线
[ 本帖最后由 江涛 于 2008-2-26 13:03 编辑 ] |
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