恒星爆炸之初（图）   

正在观测超新星2007uy 的天文学家们感到很吃惊：2008D突然出现了，起初散发出X射线（左图），随后散发出可见光。

The Beginning of a Star's Explosive End

In a stroke of unprecedented good luck, an international team of astronomers has caught a stellar explosion called supernova at the very beginning of the blast. The observation confirms several long-held assumptions about supernovae and could provide deeper insights into the workings of these cosmic firecrackers. It also could motivate scientists to push for new instruments that can catch other stars at the moment they explode.	凭借一次绝好的运气，一个由天文学家构成的跨国科研小组就在爆炸开始之时发现了被称为超新星的恒星爆炸现象。这次观测证实了好几个有关超新星长期悬而未决的设想，还有可能更加深刻地揭示这些“宇宙鞭炮”的运行机制。此次观测也会激励科学家们去努力开发新仪器，以便发现处于爆炸之初阶段的其他恒星。
Although the spectacular deaths of massive stars have been well-studied, astronomers have never been able to observe one any sooner than a few days after its beginning. Consequently, mysteries have remained about a supernova's earliest moments. The problem has been that predicting exactly when a star will go supernova is nearly impossible. And even if astronomers have some inkling that an explosion is imminent, they still must arrange observing time or frantically search for an available telescope in proper position.	尽管天文学家们对壮观的巨型恒星之死颇有研究，但是他们所能够观察到的情况均在爆炸发生好几天之后。因此，关于超新星最初阶段的情况，仍有不解之谜。问题一直在于：几乎不可能准确地预测一颗恒星究竟在何时将会变成超新星。即使天文学家们隐约地意识到爆炸即将来临，他们仍然必须安排观测时间，或者不得不去疯狂地搜寻处于合适观测位置的可利用望远镜。
The supernova called 2008D neatly and surprisingly solved such problems for its discoverers, led by astrophysicist Alicia Soderberg of Princeton University. On 9 January, she and her colleagues were using the x-ray telescope aboard NASA's Swift spacecraft to observe a month-old supernova called 2007uy, located in a galaxy called NGC 2770, nearly 90 million light-years away. Suddenly, a blinding light appeared elsewhere in the galaxy, and Soderberg and her colleagues immediately recognized it was the beginning of an entirely new supernova. They contacted colleagues across the United States and seven other countries, who quickly trained eight more telescopes and arrays on the event. In Nature tomorrow, the 43-member team reports that the characteristics of the x-ray burst they detected and then studied for 30 days conforms exactly--in terms of the brightness of the radiation, its precise rate of dimming, and the speed with which debris traveled through the galaxy--to what astronomers had been assuming for decades about the shock wave of a supernova blowing apart the outer layers of a star. They detected no gamma rays associated with the blast, confirming another prediction of the models.	这颗超新星叫做2008D，该发现巧妙而出人意料地解决了上述问题。该研究小组由普林斯顿大学天体物理学家艾丽西娅·索德伯格领导。1月9日索德伯格及同事利用美国国家航空航天管理局“雨燕”号太空飞船搭载的X射线望远镜，正在观察一颗刚刚形成一个月的超新星，这颗超新星被称为2007uy，位于一个叫做NGC 2770的星系，距地球近9,000万光年。突然，眩目的光芒出现在该星系的别处，索德伯格及同事立刻意识到这是一颗全新的超新星的开端。他们立刻联系全美的同行以及七个其他国家的同行，同行们很快将八架其他望远镜和望远镜列阵对准了该超新星。在明天出版的《自然》杂志上，拥有43名成员的研究小组报道说：他们探测到X射线的爆发特点，然后又研究了30天，发现在辐射的亮度、变暗的速率，以及恒星残骸在星系中的传播速度等方面，都跟天文学家们几十年来对超新星爆发时炸掉恒星外围的冲击波所进行的假设完全一致。研究人员没有探测到跟爆炸相关的伽马射线，证实了对此类星体的另一个预测。
"It's the first time we have seen the signature of the shock wave coming from the core collapse," says astrophysicist and co-author Neil Gehrels of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Gehrels, leader of the Swift science team, says that the most important observations of the x-ray burst were over "in an hour," but that it's important to continue following the supernova to learn more about the star. He says this experience likely will "drive the development of wide-field x-ray telescopes," which will increase the chances of discovering more supernovae at the moment of explosion.	“这是我们第一次看到来自核心塌缩的冲击波信号，”该研究的另一个发起人、马里兰州格林贝尔特美国国家航空航天局戈达德太空飞行中心的天体物理学家尼尔·格雷尔斯说。格雷尔斯是“雨燕”号太空飞船科研小组组长，他说X射线爆发最重要的观测时机在一个小时之内就结束了，但是继续跟踪研究超新星对于进一步了解恒星来说仍然很重要。格雷尔斯指出，这次经历很可能会促进广视野X射线望远镜的开发，而这种望远镜将会使研究人员拥有更多的机会，发现更多爆炸之时的超新星。
"We now have a direct observation of a star at the moment of its death," says astronomer Robert Quimby of the California Institute of Technology in Pasadena. Although the observation didn't produce any huge surprises, he says, it should aid future studies on the origins of supernovae. Of more immediate value, says astrophysicist Stanford Woosley of the University of California, Santa Cruz, the pattern of x-rays emitted by the supernova might tell researchers more precisely what sort of signatures to look for in gravitational waves and elusive neutrinos, both of which are associated with supernovae.	“我们现在直接观测到一颗处于死亡时刻的恒星，”帕萨迪纳加州理工学院的天文学家罗伯特·奎姆比说。他还说，尽管这次观测并没有发现什么特别的出人意料的情况，但是在将来对于有关超新星起源的研究应该会有所助益。提到该研究更为实际的价值时，加州大学圣塔克鲁兹分校的天体物理学家斯坦福·伍尔西指出，这颗超新星释放X射线的模式可能会使研究人员更加确切地了解到，在引力波和难以觉察的中微子中需要寻找何种信号，而引力波和中微子均跟超新星有关。