VOA科学技术2014--Discover Milky Way's Second-largest Known Black Hole

Astronomers² have discovered a black hole with a mass about 33 times greater than that of our sun. It is the second biggest black hole known in the Milky³ Way. Only the supermassive black hole at the center of the galaxy⁴ is bigger.

The newly identified black hole is about 2,000 light-years from Earth says a new study in the publication Astronomy & Astrophysics. A light year is about 9.5 trillion kilometers.

The black hole is in the constellation⁵ Aquila, and has a companion star orbiting it, researchers said on Tuesday.

Black holes are extremely dense⁶ objects. They have gravity so strong not even light can escape, making it difficult to find them. The European Space Agency's Gaia mission found the black hole. Gaia is carrying out a huge stellar count.

The scientists saw that the black hole caused its companion star to wobble. Data from the European Southern Observatory's Chile-based Very Large Telescope and other ground-based observatories⁷ confirmed the black hole's mass.

"This black hole is not only very massive, it is also very peculiar⁸," said Pasquale Panuzzo. He is a research engineer at the French research agency CNRS and lead writer of the study.

For instance, the black hole, called Gaia BH3, and its companion are traveling within the galaxy in the opposite direction of how stars usually orbit in the Milky Way.

Gaia BH3 probably formed after the supernova, or explosive death, of a star that was more than 40 times as large as the sun, the researchers said.

Black holes that result from the collapse⁹ of a single star are called stellar black holes. Gaia BH3 is the largest-known stellar black hole, said astronomer¹ and study co-author Tsevi Mazeh of the Tel Aviv University in Israel.

Stellar black holes are small compared to supermassive black holes at the center of most galaxies¹⁰. Sagittarius A* is the supermassive black hole at the heart of the Milky Way. It is 4 million times the mass of the sun and is located about 26,000 light-years from Earth.

Gaia BH3's progenitor¹¹ star was made almost entirely¹² of hydrogen and helium. Stars in the early universe were of similar chemical formation, known as low metallicity. The progenitor star had formed early in the universe's history, perhaps two billion years after the Big Bang. When it exploded at the end of its lifespan it released material into space. The remains¹³ violently collapsed¹⁴ to form a black hole.

The discovery of Gaia BH3 supports stellar evolution models showing that massive stellar black holes can be produced only by a low metallicity star like this one's progenitor star, Panuzzo said.

Gaia BH3's companion star is about 76 percent of the mass of the sun. It is a bit colder, but around 10 times brighter.

A measure called an astronomical¹⁵ unit (AU) is the distance between the earth and the sun. Gaia BH3's companion star orbits the black hole at a changing distance between 4.5 AU and 29 AU. By comparison, Jupiter orbits around 5 AU from the sun and Neptune¹⁶ around 30 AU.

Elisabetta Caffau is an Observatoire de Paris astronomer and a co-writer of the study. She said she was surprised that "the chemical composition of this companion star does not show anything special, so it was not affected¹⁷ by the supernova explosion of the black hole."

Scientists are not sure just how big stellar black holes can be.

"The maximum mass for a stellar black hole is a matter of active scientific debate," Panuzzo said.

Words in This Story

companion - n. a person or animal you spend time with or enjoy being with

mission - n. a task or job that someone is given to do

wobble - v. to move with an unsteady side-to-side motion

peculiar - adj. not usual or normal

progenitor - n. something that begins the development of something else

maximum - n. the highest number or amount that is possible or allowed

1 astronomer   

n.天文学家

参考例句：

• A new star attracted the notice of the astronomer.新发现的一颗星引起了那位天文学家的注意。
• He is reputed to have been a good astronomer.他以一个优秀的天文学者闻名于世。

2 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》

3 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。

4 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。

5 constellation   

n.星座n.灿烂的一群

参考例句：

• A constellation is a pattern of stars as seen from the earth. 一个星座只是从地球上看到的某些恒星的一种样子。
• The Big Dipper is not by itself a constellation. 北斗七星本身不是一个星座。

6 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。

7 observatories   

n.天文台，气象台( observatory的名词复数 )

参考例句：

• John Heilbron, The Sun in the Church: Cathedrals as Solar Observatories, 3-23. 约翰．海耳布隆，《教会里的太阳：教堂即太阳观测台》，第3-23页。 来自互联网
• Meteorologists use satellites, land observatories and historical data to provide information about the weather. 气象学家使用卫星、上天文台和历史资料来提供有关天气的信息。 来自互联网

8 peculiar   

adj.古怪的，异常的；特殊的，特有的

参考例句：

• He walks in a peculiar fashion.他走路的样子很奇特。
• He looked at me with a very peculiar expression.他用一种很奇怪的表情看着我。

9 collapse   

vi.累倒；昏倒；倒塌；塌陷

参考例句：

• The country's economy is on the verge of collapse.国家的经济已到了崩溃的边缘。
• The engineer made a complete diagnosis of the bridge's collapse.工程师对桥的倒塌做了一次彻底的调查分析。

10 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。

11 progenitor   

n.祖先，先驱

参考例句：

• He was also a progenitor of seven presidents of Nicaragua.他也是尼加拉瓜7任总统的祖先。
• Schoenberg was a progenitor of modern music.勋伯格是一位现代音乐的先驱。

12 entirely   

ad.全部地，完整地；完全地，彻底地

参考例句：

• The fire was entirely caused by their neglect of duty. 那场火灾完全是由于他们失职而引起的。
• His life was entirely given up to the educational work. 他的一生统统献给了教育工作。

13 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。

14 collapsed   

adj.倒塌的

参考例句：

• Jack collapsed in agony on the floor. 杰克十分痛苦地瘫倒在地板上。
• The roof collapsed under the weight of snow. 房顶在雪的重压下突然坍塌下来。

15 astronomical   

adj.天文学的，（数字）极大的

参考例句：

• He was an expert on ancient Chinese astronomical literature.他是研究中国古代天文学文献的专家。
• Houses in the village are selling for astronomical prices.乡村的房价正在飙升。

16 Neptune   

n.海王星

参考例句：

• Neptune is the furthest planet from the sun.海王星是离太阳最远的行星。
• Neptune turned out to be a dynamic,stormy world.海王星原来是个有生气、多风暴的世界。

17 affected   

adj.不自然的，假装的

参考例句：

• She showed an affected interest in our subject.她假装对我们的课题感到兴趣。
• His manners are affected.他的态度不自然。