职称英语理工类考试考前每日一练(8)

　　职称英语理工类考试考前每日一练

　　Black holes trigger stars selfdestruction

　　Scientists have long understood that supermasvive black holes weighing.Millions or billions of suns can tear apart stars that come too close.The black holegravity pulis harder on the neatest 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 JeanPierre Luminet of the Observatoire of the Paris in Meudon，France，carried out computer simulations of the final moments of such an unfortunate stars 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 he complicated by shock waves generated during the flattening process and that not nuclear explosion should occur.

　　The new simulations investigated the effects of shock waves in detail.and fund 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 de-

　　stroyed，Brassart says.Although the explosion obliterates the star，it saves some.of the starts matter from being de

　　voured by the black hole.The explosion is powerful enough to hurl much of the stars matter out of the black holes

　　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 s0，releasing ultraviolet light and Xrays.

　　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 Halperu of Columbia University in New York，US.It may make it possible to see

　　the disruption of that star immediately if it gets hot enough.

　　Brassart aggress.Perhaps it can be observed in the Xrays and gamma rays，but its something that needs to be

　　more studied，he says.Supernova researcher Chris Fryer of the Los Alamos National Laboratory in Los Almos，New

　　Mexic0.US，says the deaths of these stars are difficult to simulate，and he is not sure whether the researchers have

　　proven their case they exploded in the process.

　　1.Something destructive could happen to a star that gets too close to a black hole.Which of the following statements is NOT mentioned in the passage?

　　A.the black hole could tear apart the star

　　B.the black hole could trigger a nuclear explosion in the star

　　C.the black hole could dwindle its size considerably

　　D.the black hole could devour the star

　　2。According to the third paragraph，researchers differed from each other in the problem of

　　A。whether nuclear reaction would oecur

　　B.whether the stars would increase its density and temperature

　　C.whether shock waves would occur

　　D.whether the uneven tbrces would flatten the stars

　　3.According to the fourth paragraph，which of the tbllowing is NOT true?

　　A.No nuclear explosion would be triggered inside the star

　　B.The star would be destroyed completely

　　C.Much of the star，s matter thrown by the explosion WOuld be beyond the black holes reach

　　D The black hole would completely devomthe star

　　4。What will happen several months after the explosion of the star?

　　A.The star，s matter will move further away from by the black hole

　　B.the black holes matter will heat up

　　C.the black hole，s matter will swirl into the black hole

　　D。the black hole，s matter will release ultraviolet light and Xrays

　　5.According to the context，the worddisruptionin paragraph 6 means

　　A.confusion B.tearing apart C.interruption D.flattening