VOA标准英语2008年-Scientists Discover Milky Way's Youngest Explod

By Cindy Saine
Washington
14 May 2008

Scientists have announced the discovery of the youngest known exploding star, or supernova, in our Milky¹ Way galaxy². Astronomers³ say the remnant of the most recent supernova could provide clues to a long-standing mystery about why so few supernovae seem to explode in our galaxy, compared to other galaxies⁴. VOA Correspondent Cindy Saine reports from Washington.

Astronomers using NASA's Chandra X-ray Observatory⁵ and the Very Large Array radio telescope in New Mexico have discovered the remains⁶ of a supernova, known as "G1.9", which must have lit up our galaxy with a bright flash of light about 140 years ago.

At a NASA news conference Wednesday, scientists said they were able to estimate the age of the supernova by tracking its remnant's rate of expansion over the last 20 years. They say it expanded by 16 percent - a surprisingly large amount - indicating it is much younger than previously⁷ thought.

The scientist who led the study, Stephen Reynolds of North Carolina State University, said radio and X-ray technology allowed scientists to track the dying star through a dense⁸ field of gas and dust that had previously obscured the view.

The second most recent supernova is believed to have occurred around 1680. Ever since astronomers discovered that supernova more than 50 years ago, they have been searching for more "missing" supernovae and their remnants. Reynolds explains that scientists have measured the rates of exploding stars in other galaxies, and found out that our own Milky Way galaxy seems to be lagging behind in the number of supernovae per century.

"Large spiral galaxies like the Milky Way seem to have two or three per century," he said. "But it is clear we have not been getting our share. A half dozen or so have been reported over the last millennium⁹, but there should be 20 or 30. Now the galaxy is full of gas and dust, which could hide a distant supernova optically, but the remnant would still produce detectable¹⁰ radio waves and X-rays. This lack is a significant puzzle."

The discovery of the young remnant does not immediately provide an answer to the puzzle, but scientists say it will be a "goldmine" to study, since it is still so recent and energetic. They say it is an important finding for understanding the life cycles of stars in the Milky Way galaxy.

Bob Kirshner, of Harvard University, explains why supernovae are important for all of us.

"The supernovae make the chemical elements through real alchemy, transforming one element, the light elements into the heavy ones," he said. "So the calcium¹¹ that is in your bones and the iron that is in your blood probably came from supernovae that exploded before the sun formed. So, we are all stardust, and it seems reasonable for us to want to know how these elements get formed when stars explode."

Supernovae and their remnants create and distribute the majority of the elements in the universe, spreading everything from cobalt to gold.

1 milky   

adj.牛奶的，多奶的；乳白色的

参考例句：

• Alexander always has milky coffee at lunchtime.亚历山大总是在午餐时喝掺奶的咖啡。
• I like a hot milky drink at bedtime.我喜欢睡前喝杯热奶饮料。

2 galaxy   

n.星系；银河系；一群(杰出或著名的人物)

参考例句：

• The earth is one of the planets in the Galaxy.地球是银河系中的星球之一。
• The company has a galaxy of talent.该公司拥有一批优秀的人才。

3 astronomers   

n.天文学者，天文学家( astronomer的名词复数 )

参考例句：

• Astronomers can accurately foretell the date,time,and length of future eclipses. 天文学家能精确地预告未来日食月食的日期、时刻和时长。 来自《简明英汉词典》
• Astronomers used to ask why only Saturn has rings. 天文学家们过去一直感到奇怪，为什么只有土星有光环。 来自《简明英汉词典》

4 galaxies   

星系( galaxy的名词复数 )； 银河系； 一群（杰出或著名的人物）

参考例句：

• Quasars are the highly energetic cores of distant galaxies. 类星体是遥远星系的极为活跃的核心体。
• We still don't know how many galaxies there are in the universe. 我们还不知道宇宙中有多少个星系。

5 observatory   

n.天文台，气象台，瞭望台，观测台

参考例句：

• Guy's house was close to the observatory.盖伊的房子离天文台很近。
• Officials from Greenwich Observatory have the clock checked twice a day.格林威治天文台的职员们每天对大钟检查两次。

6 remains   

n.剩余物，残留物；遗体，遗迹

参考例句：

• He ate the remains of food hungrily.他狼吞虎咽地吃剩余的食物。
• The remains of the meal were fed to the dog.残羹剩饭喂狗了。

7 previously   

adv.以前，先前（地）

参考例句：

• The bicycle tyre blew out at a previously damaged point.自行车胎在以前损坏过的地方又爆开了。
• Let me digress for a moment and explain what had happened previously.让我岔开一会儿，解释原先发生了什么。

8 dense   

a.密集的，稠密的，浓密的；密度大的

参考例句：

• The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
• The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。

9 millennium   

n.一千年，千禧年；太平盛世

参考例句：

• The whole world was counting down to the new millennium.全世界都在倒计时迎接新千年的到来。
• We waited as the clock ticked away the last few seconds of the old millennium.我们静候着时钟滴答走过千年的最后几秒钟。

10 detectable   

adj.可发觉的；可查明的

参考例句：

• The noise is barely detectable by the human ear.人的耳朵几乎是察觉不到这种噪音的。
• The inflection point at this PH is barely detectable.在此PH值下，拐点不易发现。

11 calcium   

n.钙(化学符号Ca)

参考例句：

• We need calcium to make bones.我们需要钙来壮骨。
• Calcium is found most abundantly in milk.奶含钙最丰富。