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TSS独家报道:中子星团超量的X射线可能是暗物质候选轴子的证据

TSS EXCLUSIVE: Excess X-Ray From Neutron Star Cluster Could Be Evidence Of Dark Matter Candidate Axion

by Rhodilee Jean Dolor

天体物理学家在研究附近一群发射过多x射线的中子星时,可能发现了一种长期寻找的假设粒子的证据,这种粒子可以解释宇宙中神秘的暗物质。

Astrophysicists who have been studying a nearby group of neutron stars that emit excess amounts of x-ray may have found evidence of a long-sought hypothetical particle that can account for the mysterious dark matter in the universe. 

在1月12日发表在《物理评论快报》(Physical Review Letters)上的新论文中,伯克利实验室物理分部理论小组的分部研究员本杰明·萨夫迪(Benjamin Safdi)及其同事报告说,难以捉摸的粒子轴子可能解释了一组被称为“壮丽七号”的孤立中子星产生的大量高能x射线。

In their new paper published in Physical Review Letters on Jan. 12, Benjamin Safdi, Divisional Fellow in the Berkeley Lab Physics Division theory group, and colleagues reported that the elusive particle axion may explain the abundance of high-energy x-rays generated by a group of isolated neutron stars known as the Magnificent Seven.

什么是轴子?
What Are Axions?

轴子是理论上的粒子,在磁场的作用下变成光子。物理学家提出它们的存在是为了回答粒子物理标准模型中的一个问题,这个模型描述了基本粒子之间的相互作用。

Axions are theoretical particles that become photons in the presence of a magnetic field. Physicists proposed their existence as an answer to a problem in the Standard Model of particle physics, the framework that describes the interactions of elementary particles.

研究合著者、密歇根大学物理学研究生克里斯托弗·库奇在一份声明中说:“轴子最早是在上世纪70年代末提出的,目的是解决这个被称为强CP问题的问题,这意味着中子内部的正负电荷分布集中在同一点上。”。

“The axion was first proposed in the late 1970s to solve this problem called the strong CP problem, which means the negative and positive electric charge distributions inside the neutron are centered around the same point,” study co-author Christopher Dessert, a graduate student in physics at the University of Michigan, said in a statement.

与质子、中子和电子不同的是,轴子很少与其他粒子发生碰撞,而质子、中子和电子的行为可以在某些环境下观察到,比如在粒子加速器中。它们往往会穿过它们,这就解释了为什么科学家们发现很难证明它们的存在。

Unlike protons, neutrons, and electrons whose behavior can be observed in certain settings, such as in a particle accelerator, axions rarely collide with other particles. They tend to pass through them, which explains why scientists have found it difficult to prove that they exist.  

“你可以把轴子想象成幽灵粒子。它们可以在宇宙中的任何地方,但它们与我们的互动并不强烈,因此我们还没有对它们进行任何观察,”研究合著者、明尼苏达大学博士后研究员雷蒙德·科(Raymond co)说。

“You can think of axions as ghost particles. They can be anywhere in the universe, but they don’t interact strongly with us so we don’t have any observations of them yet,” said study co-author Raymond Co, a postdoctoral researcher at the University of Minnesota.

轴子和中微子
Axions And Neutrinos

轴子的质量非常低。它们也被认为很像中微子,亚原子粒子不带电荷,只与重力和弱力相互作用。

Axions have an incredibly low mass. They are also believed to be a lot like neutrinos, subatomic particles that carry no electrical charge and only interact with gravity and weak force.

中微子非常轻,几乎没有质量,所以它们几乎以光速运动。这些粒子是中子在中子星内部碰撞时产生的,中子星是巨星的残余,在耗尽燃料后坍塌。

Neutrinos are extremely light with nearly no mass, so they travel at nearly the speed of light. These particles are produced when neutrons collide inside neutron stars –remnants of giant stars that collapsed after exhausting their fuel.

萨夫迪和他的同事认为,轴子可以像中微子一样产生,作为中子星内部中子和质子碰撞的副产品。

Safdi and colleagues think that axions can be produced in the same way as neutrinos as a byproduct of colliding neutrons and protons inside neutron stars. 

为了研究他们的理论,他们利用密歇根大学和劳伦斯伯克利国家实验室的超级计算机来模拟中子星的内部,并预测恒星内部能产生多少轴子。

To investigate their theory, they used supercomputers at the University of Michigan and Lawrence Berkeley National Laboratory to model the interior of a neutron star and predict how many axions can be produced inside the star. 

研究人员在论文中说,轴子可以在恒星内部产生。就像中微子一样,由于轴子与物质的弱相互作用,轴子也可以在恒星外旅行。

In their paper, the researchers said that axions could be produced within the interior of the stars. Just like neutrinos, axions can also travel outside of the star because of their weak interaction with matter.

萨夫迪和同事们说,随后轴子与环绕着”壮丽七”的强磁场的相互作用可以将这些粒子转化为光子,构成望远镜可以探测到的x射线。

Safdi and colleagues said that the subsequent interaction of axions with the strong magnetic field surrounding the Magnificent Seven stars could transform the particles into photons that make up the x-rays that telescopes can detect. 

轴子比中子星发射的轻粒子有更多的能量,因此研究人员推断那些转变成光子的粒子也会有更多的能量。

Axions have more energy than the light particles that the neutron stars emit, so the researchers deduce that those converted into photons would also have more energy. 

壮丽七
The Magnificent Seven 

研究人员认为这可以解释2019年首次在“壮丽七”观测到的神秘超高能x射线。

They think this can explain the mysterious extra high-energy x-rays that were first observed in Magnificent Seven in 2019. 

星团中的所有恒星都会产生强大的磁场,但它们会产生低能的x射线和紫外线,这与许多中子星不同。这些特性使星团成为寻找轴子粒子的有利场所,因为它更容易寻找其他形式的小光流。

All stars in the cluster generate powerful magnetic fields, but they generate low energy x-rays and ultraviolet light unlike many neutron stars. These characteristics make the star cluster a favorable place to look for axion particles because it is easier to look for small streams of other forms of light. 

萨夫迪和同事已经检查了中子星后面的其他物体,但没有发现任何可以解释这次观测的原因。他们现在提出,假设的轴子可以解释壮丽七在2-8keV范围内的硬X射线过剩。

Safdi and colleagues have checked for other objects behind the neutron stars but found nothing to account for the observation. They now suggest that the hypothetical axions could explain the excess of hard x-ray emission in the 2–8 keV energy range from the Magnificent Seven stars. 

“目前还没有传统的天体物理学解释来解释壮丽七硬x射线的超量。研究人员在他们的研究中写道:“我们发现,硬x射线过剩可能是由类轴子的粒子一致解释的。”。

“No conventional astrophysical explanation of the magnificent seven hard x-ray excess exists at present. We show that the hard x-ray excess may be consistently explained by an axion-like particle,” the researchers wrote in their study.

暗物质候选者
Candidate For Dark Matter

考虑到轴子与物质的弱相互作用及其难以置信的低质量,轴子已经成为暗物质最可行的候选者之一,科学家认为暗物质是宇宙中质量缺失的原因。

Given its weak interaction with matter and its incredibly low mass, the axion has become one of the most feasible candidates for dark matter that scientists attribute for the missing mass in the universe. 

天文观测表明,构成恒星、行星和星系的可见物质不到宇宙中所有物质总质量的六分之一。科学界普遍认为,宇宙质量的80%左右是由暗物质组成的。

Astronomical observations suggest that the visible matter that makes up the stars, planets, and galaxies represent less than one-sixth of the total mass of all matter in the universe. The scientific community generally agrees that around 80 percent of the mass of the universe is made up of dark matter.

暗物质不能被直接观察到,因为它不散发光或能量。迄今为止,还没有发现暗物质的确凿证据,但研究人员根据暗物质对可见物质的引力效应推断暗物质的存在。他们认为暗物质是星系内恒星无法解释的运动背后的原因。

Dark matter cannot be observed directly because it does not emit light or energy. No solid evidence of dark matter has been detected to date, but researchers infer its existence based on its gravitational effects on visible matter. They think that dark matter is behind the unexplained motion of stars within galaxies. 

与惰性中微子、大质量弱相互作用粒子(WIMPs)、引力相互作用大质量粒子(GIMPs)、超对称粒子和原始黑洞一起,轴子是暗物质的候选粒子之一。

Along with sterile neutrinos, weakly interacting massive particles (WIMPs), gravitationally-interacting massive particles (GIMPs), supersymmetric particles, and primordial black holes, axion is one of the candidates for dark matter.

单个轴子粒子的质量可能很低,但大爆炸产生的这些粒子可能足以构成宇宙中所有的暗物质。

Individual axion particles may have low mass, but the Big Bang may have produced enough of these particles to constitute all the dark matter in the universe. 

华盛顿大学的物理学家格雷·里布卡(Gray Rybka)此前向《发现》杂志解释说:“早期宇宙的大量能量被倾倒到这些粒子中。“而且因为它们与其他任何东西都没有太多的相互作用,这些剩余的物质在宇宙中四处游荡。”

 “A whole lot of the early universe’s energy gets dumped into these particles,” University of Washington physicist Gray Rybka previously explained to the Discover Magazine. “And because they don’t interact very much with anything else, you’d have all this leftover matter kicking about the universe.” 

萨夫迪和他的团队澄清说,他们的研究并不能确定轴子的存在。比如说,他们使用了来自欧洲航天局XMM牛顿和美国宇航局钱德拉X射线天文台的数据。两者都不够灵敏,无法观察到来自轴子的其他信号。

Safdi and his team clarified that their study did not definitely establish that the axion exists. For one, they used data from the European Space Agency’s XMM-Newton and NASA’s Chandra X-ray Observatory. Both are not sensitive enough to observe other signals coming from the axion. 

研究人员承认,他们观测到的信号可能是中子星中的一个新天体物理过程。

The researchers acknowledged that the signal they observed could be a new astrophysical process in the neutron star. 

尽管如此,如果这个难以捉摸的轴子真的存在,它的发现有望彻底改变粒子物理学,让科学家更好地了解暗物质和宇宙。

Still, if the elusive axion does exist, its discovery is anticipated to revolutionize particle physics and give scientists a better understanding of dark matter and the universe.

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