Black Holes Trigger Stars to Self-Destruct
Scientists have long understood that supermassive black holes weighing millions or billions of suns can tear apart stars that come too close.The black hotels gravity pulls harder on the nearest part of the star，an imbalance that pulls the star apart over a period of minutes or hours，once it gets close enough.
Scientists say this Uneven pulling is not the only hazard facing the star.The strain of these unbalanced forces can also trigger a nuclear explosion powerful enough to destroy the star from within.Matthieu Brassart and Jean-Pierre Luminet of the Observatoire de Paris in Meudon，France1,carried out computer simulations of the final moments of such an unfortunate star’s life，as it veered towards a supermassive black hole.
When the star gets close enough，the uneven forces flatten it into a pancake shape.Some previous studies had suggested this flattening would increase the density and temperature inside the star enough to trigger intense nuclear reactions that would tear it apart.But other studies had suggested that the picture would be complicated by shock waves generated during the flattening process and that no nuclear explosion should occur.
The new simulations investigated the effects of shock waves in detail，and found that even when their effects are included，the conditions favor a nuclear explosion.“There will be an explosion of the star — it will be completely destroyed,” Brassart says. Although the explosion obliterates the star，it saves some of the star’s matter from being devoured by the black hole.The explosion is powerful enough to hurl much of the star’s matter out of the black hole’s reach，he says.
The devouring of stars by black holes may already have been observed，although at a much later stage.It is thought that several months after the event that rips the star apart，its matter starts swirling into the hole itself.It heats up as it does so，releasing ultraviolet light and X-rays.
If stars disrupted near black holes really do explode，then they could in principle allow these events to be detected at a much earlier stage，says Jules Hatpern of Columbia University in New York，US2.“It may make it possible to see the disruption of that star immediately if it gets hot enough,” he says.
Brassart agrees.“Perhaps it can be observed in the X-rays and gamma rays，but it’s something that needs to be more studied,” he says.Supernova researcher Chris Fryer of the Los Alamos National Laboratory in Los Alamos，New Mexico，US3，says the deaths of these stars are difficult to simulate，and he is not sure whether the researchers have proven their case that they explode in the process.
词汇：
supermassive adj.特大质量的
imbalance/im5bAlEns/n.不平衡，不平衡
veer/ viE/v.转向，改变方向
flatten/5flAtn/v.使成扁平，夷平
pancake/5pAnkeik/n.薄煎饼
obliterate/E5blitEreit/v.抹去，除去，消除
devour/di5vauE(r)/v.吞没;毁灭
swirl/swE:l/打旋，旋动
gamma rays γ 射线
supernova/7sju:pE5nEuvE/n.超新星
注释：
1. the Observatoire de Paris in Meudon，France：位于法国默顿的巴黎天文台。Observatoire de Paris：法文，即observatory of Paris。默顿位于巴黎西南部郊区。
2. Columbia University in New York，US：美国纽约哥伦比亚大学，长青藤联盟校之一。创建于1756年，当时名为“国王学院”。美国独立后，为了纪念发现美洲新大陆的哥伦比亚就改为哥伦比亚学院，直到1921年成为一所综合大学。1897年，该校迁址曼哈顿上城区校区。
3. the Los Alamos National Laboratory in Los Alamos，Mexico，US：位于美国新墨西哥州洛斯阿拉莫斯的洛斯阿拉莫斯国家实验室。洛斯阿拉莫斯是世界上第一颗原子弹和第一颗氢弹的诞生地，它占地110平方公里，拥有1万多名雇员，其中研究人员3 500名。