Gravitational waves from neutron star mergers could provide vital information for testing theories of the quark-gluon plasma — a hot and dense state of matter that is thought to have existed in the very early universe. That is the conclusion of physicists in Germany, who have done computer simulations of how a quark-gluon plasma could be formed when such mergers occur.
來自中子星合併的重力波可能為，驗證夸克-膠子等離子體(一種被認為存在於很早宇宙中，熱且稠密之物質狀態)的理論，提供重要資訊。那是德國物理學家們已經進行多次，當發生上述合併時，夸克-膠子等離子體，如何能被形成的電腦模擬結論。
In August 2017, the LIGO-Virgo observatories made the first-ever detection of gravitational waves from two merging neutron stars. Another merger has been since observed and more are expected — so physicists are very keen to study these gravitational-wave signals to gain insights into the violent processes that occur at the point of merger.
在2017年8月，雷射干涉儀重力波天文台(LIGO：Laser Interferometer Gravitational-Wave Observatory)與處女座(Virgo)天文台獲得了，有關來自兩顆合併中子星之重力波，有史以來的首度發現。打從那時起，另一次合併已經被觀測到，且預期有更多。因此，物理學家們非常熱衷於，研究此些重力波信號，來獲得在合併時，發生猛烈過程的洞察力。
Quantum chromodynamics was developed in the 1960s by Murray Gell-Mann and others. It explains how, under normal conditions, the strong nuclear force causes quarks to be confined by gluons to create discrete particles called hadrons – which include protons and neutrons.
量子色動力學是1960年代，由Murray Gell-Mann及其他人所發展的理論。這解釋了，在正常情況下，強核力如何導致夸克遭到膠子的束縛，而形成包括質子及中子，被稱為強子的離散粒子。
At sufficiently high temperatures and pressures, however, the hadrons dissolve into a soup of free quarks and gluons known as quark-gluon plasma or quark matter. The first convincing observations of the quark-gluon plasma were made about 20 years ago by smashing lead ions together at CERN. Since then, minute quantities of the stuff have been made at other accelerators and studied in greater detail.
不過，在夠高的溫度及壓力下，強子溶解成，被通稱為夸克-膠子等離子體，或夸克物質的自由夸克及膠子。夸克-膠子等離子體，首度令人信服的觀察，是大約20年前，於歐洲核研究中心(CERN：Center for European Nuclear Research)，藉由使鉛離子撞擊在一起獲得的。打從那時起，在其他加速器中，已經產生過微量的這種物質，且更詳細地被研究。
The quark-gluon plasma is also of great interest to physicists who study the early universe, which some models describe as have a “quark epoch” from about 10−12-10−6 s after the Big Bang.
夸克-膠子等離子體也引起了，研究早期宇宙(在大爆炸後，大約10−12-10−6秒內，一些模型描述為“夸克時期”)之物理學家們極度的興趣。
Too hot and dense for quarks to be bound into hadrons, the universe in the quark epoch is thought to have comprised a quark-gluon plasma. Understanding the detailed properties of this state of matter therefore helps cosmologists model the universe’s evolution further back towards the Big Bang.
夸克太熱且稠密，無法被束縛成強子。在夸克時期的宇宙，被認為已經具有夸克-膠子等離子體。因此，瞭解這種物質態的詳細屬性，有助於宇宙論學家們製作，遠溯至大爆炸的宇宙演變模型。
An open question is whether stable quark-gluon plasma exists naturally in the observable universe today. “In 1984, Edward Witten proposed that quark matter is the fundamental state of matter,” explains theoretical astrophysicist Luciano Rezzolla of the Institute for Theoretical Physics in Frankfurt.
一項懸而未決的問題是，在當今可觀測的宇宙中，是否自然存在，穩定的夸克-膠子等離子體。德國理論物理研究所(位於法蘭克福市)的理論天體物理學家，Luciano Rezzolla解釋：「於1984年，Edward Witten提出了，夸克物質是物質的基本態。」
Many astrophysicists had once believed that entire stars can be made of quark matter, but more recent observations have made this a minority view: “If you asked a roomful of scientists how many of them think pure quark stars exist, you would find only a few hands raised,” says Rezzolla.
諸多天體物理學家曾經認為，全部恆星皆可能由夸克物質組成。不過，最近諸多觀測結果，已經使得上述成為少數人的觀點。Rezzolla宣稱：「倘若問滿座的科學家，其中有多少人，認為存在純夸克星，則會發現舉起的手，僅少數幾隻。」
More plausible, explains Rezzolla’s PhD student Lukas Weih, are hybrid stars with “degenerate quarks in the centre where the pressure is highest, and then around this a normal neutron star”.
Rezzolla的博士生， Lukas Weih解釋說，更似合理的是，具有“簡併夸克在壓力最高的中心，然後一顆正常中子星圍繞此中心”的混合恆星。
The neutron stars with the highest central pressure would be the heaviest ones, which raises the intriguing possibility of two lighter neutron stars in a binary orbit merging and undergoing a phase transition to a such a heavy hybrid star. However, there is little agreement on under what circumstances, or exactly how, this would occur.
具有最高中心壓力的中子星，會是最重的中子星。這引發了，在雙星軌道中，兩個較輕的中子星合併，且經歷相變到上述混合恆星之引人感興趣的可能性。不過，有關在什麼狀況下，也就是，這確切會如何發生，鮮少有一致的看法。
In the new research, Rezzolla, Weih and Matthias Hanauske compared computer models of mergers between binary neutron stars with equal masses either 2.64 or 2.68 times that of the Sun. The models predicted the gravitational wave signals produced in such mergers.
在這項新研究中，Rezzolla、Weih及Matthias Hanauske比較了，具有質量等於太陽2.64或2.68倍之雙星中子星間，合併的電腦模型。這些模型預測了，這種合併過程中，產生的重力波信號。
The signals produced if no phase transition occurs, or if an immediate phase transition occurs on merger, had been previously calculated by other research groups. The Frankfurt researchers simulated a phase transition-triggered core-collapse leading to black hole formation; and a gradual post-merger phase transition to a hybrid neutron star with a quark-gluon plasma in its centre.
其他研究團隊先前已經推測了，倘若沒有發生相變，或合併時立即發生相變產生的信號。德國理論物理研究所的研究人員們模擬了，導致形成黑洞之相變觸發的核心塌陷，及合併後逐漸相變到，在其中心具有夸克-膠子等離子體的混合中子星。
If no phase transition occurs, for example, the frequency of the gravitational waves after the merger should remain constant over time. If the star undergoes a gradual phase transition, however, their frequency should climb over the course of a few milliseconds.
譬如，倘若沒有發生相變，則合併後的重力波頻率，應隨著時間推移保持恆定。不過，如果這種恆星經歷逐漸的相變，則其頻率應在幾毫秒的進程內，攀升。
“Also, if you do some signal processing, you will find that the purely hadronic case gives you one peak in the frequency spectrum,” explains Weih, “whereas if there is a [gradual] phase transition to quark-gluon plasma, you also get a second peak.”
Weih解釋：「同樣地，倘若進行一些信號處理，則會發現純強子狀況，在此頻譜中產生一個高峰。反之，倘若有逐漸過渡到夸克-膠子等離子體的相變，則也會獲得第二個高峰。」
The research is described in a paper in Physical Review Letters. “This is a very interesting paper,” says astrophysicist David Radice at Pennsylvania State University in the US.
該項研究在《物理評論記事》期刊的一篇論文中，被記述。美國賓州州立大學天體物理學家，David Radice宣稱：「這是一篇，非常引人感興趣的論文。」
“It’s not the first paper to look at the impact of phase transitions in neutron star binaries, but people in the past have taken one particular model for how matter should behave at high densities and performed simulations with that. But there are many different models all predicting different things, and here they’ve parameterized this uncertainty and considered all possibilities.”
「這不是探究有關中子星雙星中，相變影響的第一篇論文。不過，過去人們就物質在高密度下會如何表現，採取了一種獨特的模型，並使用它進行了模擬。不過，有諸多全預測不同事物的不同模型。因此在這裡，他們已經將這種不確定性參數化，並考慮了所有可能性。」
He cautions, however, that interpretation of gravitational wave data is an embryonic art: “Many things are uncertain,” he says, “For example, there may be reasons why two characteristic frequencies appear in the post-merger signal that have nothing to do with a phase transition.”
不過，他警告說，引力波數據的解釋是一種，初期的方法。他宣稱：「諸多事情是不確定的。譬如，可能有諸多原因，合併後的信號中，出現兩種與相變無關的獨特頻率。」
原文網址：https://physicsworld.com/a/gravitational-waves-from-neutron-star-mergers-could-reveal-quark-gluon-plasma/
翻譯：許東榮
文章定位：
