Black Holes Trigger Stars to Self-destruct Scientists have long understood that supermassive(超大质量的)black holes weighing millions or billions of suns can tear apart stars that come too close. The black hole’ s 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(巴黎天文台)in Meudon, France, carried out computer simulations of the final moments of such an unfortunate star’ s life, as it veered(改变方向)towards a supermassive black hole. When the star gets close enough, the uneven forces flatten it into a pancake(薄饼)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(使消失)the star, it saves some of the star’ s matter from being devoured(吞没)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(旋转)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 Halpern 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,“he says.

He wore a shabby thin overcoat in the cold winter so that he fell ill. old big new small

The umbrella was ingeniously devised to fold up into the pocket. seriously cleverly attentively carefully

His answers were obscure and confusing. unclear obvious clear direct

The way she looked after her young sister was really touching. disturbing connecting moving waving

Sports Star Yao Ming If Yao Ming is not the biggest sports star in the world, he is almost certainly the tallest. At 2.26m, he is the tallest player in the National Basketball Association(NBA)and holds the record as the most towering Olympian ever to compete in the Games. But what really stands out about the giant center is his celebrity(名气). Few, if any, Chinese athletes are as well-known as Yao around the world. People across the globe are fascinated with Yao, not only for his basketball prowess(杰出的才能),but also for being a symbol of international commerce. When Yao joined the Houston Rockets as the No. 1 pick in the 2002 NBA draft(选拔), he was the first international player ever to be selected first. His assets on the court are clear enough— no NBA player of his size has ever possessed his mobility, so he is a handful(难对付的人)for op ponents on either end of the court. But what makes Yao invaluable to the Rockets organization is his role as a global citizen and as a bridge to millions of potential basketball fans in China. When it was announced in February that Yao would miss the rest of the NBA season and possibly the Olympics with a stress fracture(骨折)in his left foot, a collective shudder(震动)spread across China. After considerable debate and discussion, Yao opted to get his foot surgically treated in an operation that placed several tiny screws across the bone, to offer his overburdened foot more support. The surgery was a success, and though the estimated four-month recovery period will leave him little time to prepare with Team China, Yao has vowed to be ready for the Beijing Olympics. Yao wrapped up a 10-day trip to China, where he underwent a series of traditional Chinese medicine(TCM)treatments, hoping to accelerate his recovery process. Western experts are generally skeptical of TCM’ s benefits, although new research from the University of Rochester suggests that a certain compound derived from shellfish may indeed stimulate bone repair. “ There is no reason to dismiss TCM,“ Yao told a press conference in Beijing. “ It’ s been used in our country for thousands of years. I don’ t think that it’ s short on science. “

The coastal area has very mild winter, but the central plains remain extremely cold. severe hard warm dry

She is an artist whose work will undoubtedly withstand the test of time. grade attract bear suffer

The weather was so gorgeous that many people went outing. uncontrollable pleasant cloudy unbearable

Some newspapers in the west are notably biased. especially wholly totally fairly

The new garment fits her perfectly. clothes haircut purse necklace

Income Tax For many young Americans, graduating from college means finding a job, moving out of the dorm room and beginning to register one’ s annual earnings with the US government. That last item is the law,though sometimes it’ s a hassle(难事)to obey. Independent tax advisor Bob Gilbert calls the US income tax system “amazingly complicated“. But he adds that “ very little of the complicated tax law applies to young people who are just beginning their careers“. According to Gilbert, 80 to 90 percent of Americans are not really burdened by the system’ s complications. Still, all the numbers and forms can be a little confusing to those who are just starting their careers. Some pull out their calculators and try to do the math alone. Some use income tax software. Others just hand the whole responsibility over to tax firms like Gilbert’ s. According to income tax law expert Linda Beale,young people will often follow their parents’ lead when filling their income forms. “Young people who grow up in wealthy households typically use professional tax services because their parents have always done so,“ said Beale, a professor at Wayne State University in Michigan State. “ On the other hand, most poorer young people probably try to do their own taxes, unless they want a quick ’ refund’ with the help of a tax advisor. “ In fact, obeying the law has its benefits. For one,many young people can expect a tax refund. This means that, over the course of the year, they have paid too much in monthly federal or state taxes and are entitled to the difference. Bob Thalman, a 20-year-old university student, expects he will get a refund of about $ 100, which will probably go in the bank, or perhaps be used to pay for car insurance or credit card bills. Thalman called the whole process a “hassle“ ,but added that he didn’ t want to test the law by not filling his income tax papers. “I’m worried about what would happen if I failed to file,“ he said. “ I know one individual who did not report his income tax for many years, and he’ s now in federal prison. I certainly don’ t want that. “

Tunguska Event 1 A hundred years ago this week, a gigantic explosion ripped(撕裂)open the dawn sky above a forest in western Siberia, leaving a scientific riddle that endures to this day. 2 A dazzling light pierced the heavens, followed by a shock wave as strong as 1,000 atomic bombs. The explosion flattened 80 million trees across an area of 2,000 square kilometers. The fireball was so great that, a day later, Londoners could read their newspapers under the night sky. What caused the so-called Tunguska Event, named after the nearby Podkamennaya Tunguska river, still remains a mystery. 3 Experts suspect it was a rock that, after traveling in space for millions of years, was destined to crash to Earth at exactly 7:17 a. m. on June 30,1908. This possibility worries scientists. “Imagine an unspotted asteroid(小行星)hitting a significant chunk(块)of land. .. and imagine if that area, unlike Tunguska, were populated,“ the British science journal Nature commented recently. 4 But no fragments of the “rock“ have ever been found. Finding such evidence would be important, for it would increase our knowledge about the risk posed by dangerous Near Earth Objects(NEOs),say Italian researchers Luca Gasperini, Enrico Bonatti and Giuseppe Longo. When the next Tunguska NEO approaches, scientists will have to decide whether to try to deflect(使偏转)it or blow it up in space. 5 However, several rival theories for the Tunguska Event exist. Wolfgang Kundt, a professor at Germany’s Bonn University, believes the Tunguska Event was caused by a massive escape of 10 million tons of methane(甲烷)-rich gas from deep within earth’ s crust. Some people hold that the explosion was caused by an alien spaceship crash, or a black hole in the universe. A Competing Explanations B Unknown Attacks C Mysterious Explosion D Star War E Importance of Finding Evidence F Explanation That Worries Scientists

Don’t Rely on Indirect Evidence Conservationists may be miscalculating the numbers of the threatened animals such as elephants, say African and American researchers. The error occurs because of a flaw in the way they estimate animal numbers from the piles of dung(粪)the creatures leave behind. The mistake could lead researchers to think that there are twice as many elephants as there really are in some regions, according to Andrew Plumptre of the Wildlife Conservation Society(WCS)in New York. Biologist Katy Payne of Cornell University in Ithaca, New York, agrees. “ We really need to know elephant numbers and the evidence that we have is quite indirect,“ says Payne, who electronically tracks elephants. Counting elephants from aeroplanes is impossible in the vast rainforests of Central Africa. So researchers often estimate elephant numbers by counting dung piles in a given area. They also need to know the rate at which dung decays. Because it’ s extremely difficult to determine these rates, however, researchers tallying(统计)elephants in one region tend to rely on standard decay rates established elsewhere. But researchers at the WCS have found that this decay rate varies from region to region depending on the climate and environment. Using the wrong values can lead the census astray(歧途), says Plumptre. He and his colleague Anthony Chifu Nchanji studied decaying elephant dung in the forests of Banyany-Mbo wildlife sanctuary(禁猎区)in Southwest Cameroon. They found that the dung decayed between 55 and 65 per cent more slowly than dung in the rainforests of neighboring Gabon. If researchers use decay rates from Gabon to count elephants in Cameroon, they would probably find more elephants than are actually around. This could mean estimates in Cameroonare at least twice as high as those derived from decay rates calculated locally, says Plumptre. “However accurate your dung density estimate is,the decay rate can severely affect the result. “ Plumptre also says that the dung-pile census should be carried out over a region similar in size to an elephant’ s natural range. The usual technique of monitoring only small, protected areas distorts numbers because elephants move in and out of these regions, he says. “ If the elephant population increases within the protected area, you can not determine whether it is a real increase or whether it is due to elephants moving in because they are being poached(偷猎)outside. “ Plumptre says that similar problems may also plague other animal census studies that rely on indirect evidence such as nests, tracks or burrows(地洞).

Only people over 18 are eligible to vote. honest qualified enabled clever

The latest car model embodies the new research development. lists includes borrows broadens

Competitors must abide by the judge’ s decision. keep read understand obey

We are worried about this fluid situation full with uncertainty. stable suitable changeable adaptable

They have built canals to irrigate the desert. decorate change visit water

The details of the costume were totally authentic. outstanding real creative false

A has remained a puzzle B lacks sufficient evidence C is a university professor D was generated by the explosion E will kill many animals F are attacked by aliens

What would take place if a star gets too close to a black hole?

According to Paragraph 3 , reseachers differed in the likehood of generating______.

According to Paragraph 4, the new simulations favored______.

What is supposed to happen several months after the explosion of the star?

The word “disruption“ in Paragraph 6 means .