（轉載+翻譯）低頻引力波可以解開宇宙起源的奧秘（inverse）
轉載自https://www.inverse.com/science/low-frequency-gravitational-waves，原文章標題為FINDING THIS COSMIC PHENOMENON COULD UNLOCK?MYSTERIES?OF THE ANCIENT UNIVERSE，作者為PASSANT?RABIE，發(fā)布時間為2021年10月20日。
Low frequency gravitational waves could unlock the secrets of the ancient universe.
Astronomers are on the verge of unlocking an entirely new way to observe the universe.
天文學家即將解鎖一種新的觀測宇宙的方式。
Since the first detection of gravitational waves in October 2015, scientists have been listening in to these cosmic hums caused by massive, violent events such as the merger between two black holes.
從2015年10月首次探測到引力波以來，科學家一直在收聽這種如兩個黑洞合并這樣的大質量的、劇烈的事件引起的宇宙之聲。
But scientists still can’t detect these waves at low frequencies that are often the result of even more massive objects colliding with one another or events that took place shortly after the Big Bang.
但是科學家仍然無法探測低頻的引力波，這種引力波通常是質量更大的物體相撞或者宇宙大爆炸后不久發(fā)生的事件造成的。
A team of researchers from the University of Birmingham suggests combining different methods to detect ultra low-frequency gravitational waves that hold the mystery of ancient black holes and the early universe.
伯明翰大學的一個研究團隊建議結合不同的方法來探測極端的低頻引力波，這種引力波含有古老的黑洞和早期宇宙的奧秘。
Their?work?was published Monday in the journal?Nature Astronomy.
他們的研究成果被發(fā)表在了《Nature Astronomy》上。
WHAT ARE LOW-FREQUENCY GRAVITATIONAL WAVES?
什么是低頻引力波？
Astronomers have mainly relied on electromagnetic radiation, or light, to study objects in space. But as light travels towards us, it interacts with different elements in outer space, including dust, obscuring our view of the cosmos.
天文學家主要依賴于電磁波來研究空間中的物體。但是當光向我們傳播時，它會和太空中的包括塵埃在內的不同現(xiàn)象發(fā)生作用，這模糊了我們觀測宇宙的視野。
Gravitational waves are a way to listen to the universe rather than see it. These hums are caused by the accelerated masses of cosmic beings, which send out ripples through spacetime at the speed of light. Scientists can listen in on these echoes of the cosmos thanks to the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors and the Virgo detector.
引力波是一種聽見宇宙而不是看見宇宙的方式。這些“聲音”是由宇宙中大量物質的加速造成的，它們以光速在宇宙時空中掀起漣漪。得益于雷射干涉重力波天文臺（LIGO）和室女座干涉儀，科學家可以聽到這些宇宙的回響。
But most of the gravitational waves detected so far have been of higher frequencies in the millihertz. Meanwhile, low-frequency gravitational waves, which are in nanohertz frequencies, are much more challenging to detect.
但是現(xiàn)在探測到的大多數引力波頻率都比毫赫茲更高。與此同時，納赫茲頻率的低頻引力波的探測更加富有困難和挑戰(zhàn)性。
Frank Ohme, leader of the Independent Max Planck Research Group for Gravitational Physics, explains that they oscillate faster or slower depending on what causes the gravitational waves.
馬克思·普朗克獨立引力物理研究小組的領導人弗蘭克·歐姆解釋這些引力波頻率的高低取決于引起它的原因。
“The effect is the same; it's got to stretch and squeeze space and time,” Ohme tells Inverse. “The low-frequency ones want to do it slower, so it takes a lot longer for things to squeeze and stretch than the high-frequency ones.”
“效果是一樣的：它在拉伸和擠壓時空，”歐姆告訴Inverse，“這些低頻的想要更慢，所以與高頻的相比花費了更多的時間來擠壓和拉伸?！?/p>
While high-frequency gravitational waves are caused by ordinary stars or smaller black holes between 20 to 30 solar masses, low-frequency waves are caused by the merger of supermassive black holes, which can be millions or billions of times the mass of the Sun.
高頻引力波是由普通的恒星和更小的黑洞（質量在20到30個太陽質量之間）產生的。低頻引力波是由特大質量的黑洞融合產生的，它們的質量可以是數百萬或者數十億倍的太陽質量。
Scientists also believe that low-frequency gravitational waves could come from events taking place shortly after the Big Bang, long before galaxies were formed.
科學家也相信低頻引力波可能來自大爆炸后不久發(fā)生的事件，遠早于星系形成。
HOW TO DETECT LOW-FREQUENCY GRAVITATIONAL WAVES
如何探測低頻引力波
Christopher Moore, a researcher at the Institute for Gravitational Wave Astronomy & School of Physics and Astronomy at the University of Birmingham and lead author of the paper, has been studying gravitational waves for several years.
這篇論文的主要作者、伯明翰大學引力波天文研究所和物理與天文學院的研究者克里斯托弗·摩爾已經研究引力波好幾年了。
“I’ve long been interested in gravitational waves,” Moore tells Inverse. “But for most of my time, low-frequency waves have been a niche interest with a lot less attention than the high-frequency stuff, but I think that’s really starting to change.”
“我一直對引力波很感興趣，”摩爾告訴Inverse，“但是在我的大部分時間中，與高頻引力波相比，低頻引力波是一個投入了少得多的注意力的小眾興趣。但是我認為這一點確實開始改變了?！?/p>
The primary method used to detect low-frequency gravitational waves is through pulsars, compact, highly magnetized stars that rotate while emitting a regular pulse of radio waves. Scientists look for any fractional change to the timing of the pulsar’s beam that gravitational waves may cause.
探測低頻引力波的主要方法是通過脈沖星，脈沖星是一種旋轉的高密度、強磁場的中子星，并會發(fā)出規(guī)律性的電磁波?？茖W家在尋找任何可能是引力波導致的脈沖星波束的微小的變化。
“Nature has been kind enough to give us rapidly spinning millisecond pulsars, which are extremely good clocks — they rotate in a very, very stable way which makes them extremely good timekeeping instruments,” Moore says. “If a gravitational wave were to come across the Earth, you'd see the clocks speed up and slow down but in different ways.”
“自然足夠友善地給了我們快速旋轉的毫秒脈沖星，它們是很好的時鐘——它們以一個非常固定的方式旋轉，這讓它們成為了非常好的計時工具?！蹦栒f，“如果一束引力波穿過地球，你會看到時鐘以不同的方式加速和減速?！?/p>
But while that may be the leading way to detect low-frequency gravitational waves, the authors behind the new study argue that it’s not enough since it doesn’t specify the cause behind the waves.
雖然這可能是探測低頻引力波的主要方式，但是這個它的研究者爭論這種方式并不足夠，因為它并沒有詳細說明引力波的起因。
Instead, they suggest combining different methods to determine the source of low-frequency gravitational waves.
作為替代，他們建議結合不同的方法查明低頻引力波的來源。
In January, the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) detected what may be hints of low-frequency gravitational waves by studying signals from distant stars, but those are yet to be confirmed.
在一月，北美納赫茲引力波天文臺（NANOGrav）通過研究來自遙遠星球的信號探測到了可能是低頻引力波的線索，但是它們還沒被確認。
“So what we were really trying to do in this paper is to see if there's any other probe, apart from pulsar timing, any other instrument, any other experiment, any way of trying to detect gravitational waves that could help, even a little bit,” Moore says.
“所以我們在這篇論文中實際在嘗試去做的是尋找是否有任何除了脈沖星計時之外的任何其它可能會有幫助的設備、實驗或方法來探測引力波，即使只是一點點?！蹦栒f。
One suggestion is combining the pulsar data with observations made by the European Space Agency's Gaia mission, which has the ambitious task of creating a three-dimensional map of the Milky Way.
一個建議是將脈沖星數據和歐空局（ESA）蓋亞（Gaia）計劃的觀測結合，蓋亞計劃有創(chuàng)建銀河系三維地圖的宏大任務。
The authors also suggest looking into Big Bang nucleosynthesis, a model of the early universe based on how many different atoms existed shortly after the Big Bang.
作者還建議調查宇宙大爆炸的核合成，一種基于宇宙大爆炸后不久存在的原子種類數量的早期宇宙模型。
“So neither of those methods can detect gravitational waves yet, but they can place limits at different frequencies,” Moore says.
“所以這些方法都不可以探測到引力波，但是可以對不同的頻率進行限制?！蹦栒f。
Although the paper does not come up with conclusive answers, it is a first step in conducting future studies on low-frequency gravitational waves.
雖然這篇論文并沒有得到結論性的答案，它仍是未來實施研究低頻引力波的第一步。
WHY DO WE STUDY GRAVITATIONAL WAVES?
我們?yōu)槭裁匆芯恳Σǎ?/h1>
Since researchers first detected gravitational waves, these ripples through spacetime have opened up a new field for observing the universe.
自從研究人員第一次探測到引力波，這些穿過時空的漣漪開啟了觀察宇宙的一個新領域。
And now, as scientists are on the verge of unlocking low-frequency gravitational waves, it’s an exciting time to be listening in to the cosmos.
現(xiàn)在，科學家在解鎖低頻引力波的邊緣，這是一個令人激動的聽到宇宙的時刻。
“We just tap into the really massive black holes that we know exist in the universe, but we’re not exactly sure how many there are and how heavy they are,” Ohme says. “And because they are so heavy, the gravitational waves they create not only are of lower frequencies but also are super, super loud intrinsically.”
“我們只利用了我們知道存在的大質量黑洞，但是我們并不確切地知道它們數量有多少、質量有多大?！睔W姆說，“因為它們是如此的重，它們創(chuàng)造的引力波本質上不僅頻率低，還非常的強烈?！?/p>
“So the heavier the black holes are, the larger spacetime distortion they create, and therefore we can look further out into the universe,” he adds.
“所以黑洞質量越大，就能創(chuàng)造越大的時空扭曲，因此我們可以向宇宙看得更遠?！彼a充。
But for low-frequency gravitational waves to be informative, scientists have to know their source.
因為低頻引力波可以提供許多信息，所以科學家必須知道它們的起源。
“And that’s really the point, are we looking at an astrophysical signal coming from black holes in the local universe, or are we looking at a cosmological process happening, happening much closer to the Big Bang, much further back in time?” Moore says.
“并且這確實是重點，我們在看向來自黑洞的天體物理學信號，還是我們在看向發(fā)生的宇宙演變過程，在時間上比宇宙大爆炸更加接近還是更加遙遠？”摩爾說。
Moore predicts that scientists are on the verge of the first confirmed detection of low-frequency gravitational waves, which may help us peer further out into the universe or learn more about how supermassive black holes came to be in the first place.
摩爾預測科學家在首次確認探測到低頻引力波的邊緣，這可能可以幫助我們看向更遠的宇宙或者了解更多關于大質量黑洞如何形成的知識。
“It’s a completely new way of doing astronomy,” Moore says. “That’s one of the things that makes it really exciting.”
“這是一種全新的天文研究方法，”摩爾說，“這是它確實令人激動的原因之一?！?/p>
Abstract:
Gravitational waves at ultra-low frequencies (?100?nHz) are key to understanding the assembly and evolution of astrophysical black hole binaries with masses ~106–109M⊙ at low redshifts1–3 . These gravitational waves also offer a unique window into a wide variety of cosmological processes4–11. Pulsar timing arrays12–14 are beginning to measure15 this stochastic signal at ~1–100?nHz and the combination of data from several arrays16–19 is expected to confirm a detection in the next few years20. The dominant physical processes generating gravitational radiation at nHz frequencies are still uncertain. Pulsar timing array observations alone are currently unable21 to distinguish a binary black hole astrophysical foreground22 from a cosmological background due to, say, a first-order phase transition at a temperature ~1–100?MeV in a weakly interacting dark sector8–11. This letter explores the extent to which incorporating integrated bounds on the ultra-low-frequency gravitational wave spectrum from any combination of cosmic microwave background23,24, big bang nucleosynethesis25,26 or astrometric27,28 observations can help to break this degeneracy.
（第一次做翻譯，質量并不高，如發(fā)現(xiàn)錯誤請在評論區(qū)中指出，感謝幫助）
