VOA科学技术2023--Scientists Observe Gravitational Waves Linked to Black Holes for the First Time

Scientists Observe Gravitational Waves Linked to Black Holes for the First Time

Scientists say that, for the first time, they have observed gravitational waves caused by black holes and other huge space objects moving through the universe.

A group of international scientists using radio telescopes in North America, Europe, China, India and Australia made the observation.

The existence of gravitational waves was first predicted more than 100 years ago by physicist¹ Albert Einstein as part of his General Theory of Relativity. Einstein's theory proposed that gravity is caused by a curving of space and time.

Scientists believe that, as gravitational waves travel through space, they press against and stretch everything they pass through. But researchers have struggled for many years to find solid evidence of the waves. In the 1970s, researchers found indirect proof by studying the motion of two crashing stars. That work was honored as part of the 1993 Nobel Prize in physics.

Then, in 2016, astronomers² announced they had detected the first direct evidence of gravitational waves. That evidence came from an American-based research project known as the Laser Interferometer Gravitational-Wave Observatory³, or LIGO. The LIGO project used ground-based telescope instruments to detect a gravitational wave produced when two black holes crashed into each other about 1.3 billion light years from Earth.

But the LIGO effort was only able to pick up waves at high frequencies. In the latest research, scientists were attempting to find low-frequency waves as a way to confirm gravitational wave signals.

The researchers said they successfully discovered such signals using about 15 years of data from a project called NANOGrav. This project has long used telescopes across North America to search for low-frequency gravitational waves. The results were recently published in a study in The Astrophysical Journal of Letters.

The research involved scientists aiming a series of radio telescopes at dead stars called pulsars. The pulsars send out radio wave signals as they spin around in space. These signals are so predictable that scientists know exactly when the radio waves are supposed to arrive on Earth. The pulsars are like "a perfectly⁴ regular clock ticking away far out in space," said NANOGrav member Sarah Vigeland. She is an astrophysicist at the University of Wisconsin-Milwaukee.

But gravitational waves can affect the distance between Earth and the pulsars, which can change the signal activity. The researchers examined small changes in the ticking rate across 68 different pulsars. Some signals came early while others came late. The scientists said this research method provided enough evidence that gravitational waves were passing through.

So far, this method has not been able to identify exactly where these low-frequency waves are coming from, said Marc Kamionkowski. He is an astrophysicist at Johns Hopkins University who was not involved with the latest research.

But Kamionkowski told The Associated Press the process does demonstrate how low-frequency gravitational waves appear to produce a continuous background "noise." He compared the sound to what a person hears when standing⁵ in the middle of a party. "You'll hear all of these people talking, but you won't hear anything in particular," Kamionkowski said.

The discovered background noise is "louder" than some scientists had expected, said Chiara Mingarelli. She is a member of the NANOGrav team and an astrophysicist at Yale University. Mingarelli told the AP this could mean there are more, or bigger, incidences of black holes coming together in space than previously⁶ thought.

Or it may suggest there could be other sources of gravitational waves that could raise new questions about the formation of the universe. For example, another theory is that gravitational waves could be left over from a fast expansion period that came right after the Big Bang. The Big Bang is the explosion many scientists believe created the universe.

Michael Keith was a member of the research team and works with the European Pulsar Timing⁷ Array, a collection of research telescopes. He said the galaxies⁸ between Earth and the Big Bang were likely "drowning out" such gravitational waves.

In the future, scientists say low-frequency gravitational waves could provide even more information about early expansion of the universe. In addition, such a study could also help expand research on the mysteries of dark matter.

Words in This Story

curve – v. to form a curve: a line that bends continuously and has no straight parts

detect – v. to find or discover

frequency – n. the number of times a wave is produced within a particular period

tick – n. the sound a clock or watch makes each second when keeping time

source – n. where something comes from

1 physicist   

n.物理学家，研究物理学的人

参考例句：

• He is a physicist of the first rank.他是一流的物理学家。
• The successful physicist never puts on airs.这位卓有成就的物理学家从不摆架子。

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 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。

4 perfectly   

adv.完美地，无可非议地，彻底地

参考例句：

• The witnesses were each perfectly certain of what they said.证人们个个对自己所说的话十分肯定。
• Everything that we're doing is all perfectly above board.我们做的每件事情都是光明正大的。

5 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

6 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。

7 timing   

n.时间安排，时间选择

参考例句：

• The timing of the meeting is not convenient.会议的时间安排不合适。
• The timing of our statement is very opportune.我们发表声明选择的时机很恰当。

8 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。