内容来源：https://www.quantamagazine.org/astrophysicists-find-no-hair-on-black-holes-20250827/

内容总结：

【天体物理学新突破：爱因斯坦黑洞理论再获验证】
近年来，科学家通过分析黑洞合并产生的引力波信号，对爱因斯坦广义相对论中黑洞“无毛定理”进行了迄今最严格的检验。最新研究显示，黑洞仅由质量与自旋两个参数决定，未发现其他特征性结构（即“毛发”）。这一结论基于对22次黑洞碰撞事件的联合数据分析，结果以95%的置信度表明，黑洞事件视界外40公里内未出现偏离广义相对论的现象。

尽管量子理论曾预言黑洞可能存在由量子效应引发的微观“毛发”（如“防火墙”或“模糊球”模型），但当前观测精度尚未能探测到此类迹象。未来，随着中国参与的国际引力波探测网络（包括LIGO、Virgo、KAGRA及印度新建观测站）的升级，以及下一代“宇宙探索者”和“爱因斯坦望远镜”的投入使用，人类有望在足球场尺度的精度上进一步检验相对论，或揭示现有理论未能预见的全新物理现象。

本研究由全球多国团队合作完成，相关成果已于2023年5月底发布。科学家强调，此次验证不仅巩固了爱因斯坦理论的基石，也为破解“黑洞信息悖论”这一现代物理学的核心难题提供了关键观测约束。

中文翻译：

天体物理学家发现黑洞无"毛发"

引言
根据阿尔伯特·爱因斯坦的广义相对论，黑洞的行为仅取决于两个参数：质量与旋转速度。这就是全部。学界认为黑洞"无毛发"——即与同等质量和自旋的黑洞相比，它们不存在任何区分性特征。

随着新数据的出现，检验这种无毛发猜想逐渐成为可能。过去十年间，天文学家已探测到数百个黑洞碰撞信号。在这些剧烈事件中，时空结构中的两个不可见深渊彼此环绕且不断加速，最终融合成一个巨型黑洞，如同果冻般在碰撞后持续颤动。这种融合与颤动产生的引力波如同涟漪般穿过宇宙结构，最终被地球的探测器捕获。若广义相对论正确，这些颤动应具有标准模式，仅取决于每个黑洞的质量与自旋（理论上还存在第三属性——电荷，但实际天体黑洞的净电荷可忽略不计）。若理论有误，天文学家或能观测到新现象——那些揭示每个黑洞独特历史与构成的微妙差异。

"随着时间推移与事件累积，我们意识到可以对（广义相对论）理论或其替代理论进行更强有力的检验，"哥本哈根尼尔斯·玻尔研究所物理学家维托尔·卡多佐表示。

卡多佐与数十位引力波天文学家近期总结了这些检验的进展。他们于五月底发布的报告涵盖多种方法与结果，包括卡多佐团队去年秋季对引力波信号的分析。通过整合多个黑洞碰撞数据，该团队发现数据与爱因斯坦理论高度吻合。任何偏离广义相对论预测的黑洞时空结构特征——任何"毛发"——都必须存在于距黑洞40公里范围内。

目前尚未观测到毛发存在。但理论学家持续探索各种可能性，指出爱因斯坦理论存在的裂缝表明量子"毛发"理应存在，尽管探测难度极大甚至可能无法实现。

爱因斯坦未预见的难题
黑洞毛发问题与现代物理学最大谜题紧密相关：如何将广义相对论与量子理论融合？

以物体跨越黑洞事件视界（不可折返点）为例。根据广义相对论，外界仅能获知被吞噬物体如何影响黑洞的两个参数：增加的质量以及改变的黑洞旋转速度。

然而关于被吞噬物体所有其他信息的消失，与量子力学核心原则相冲突。量子理论要求所有信息必须保留且在理论上可获取——否则量子概率无法如必需那般总和为100%。理论物理学家长期痴迷于广义相对论与量子力学预测间的这种矛盾，即所谓信息悖论。

2012年，物理学家证明该悖论与事件视界的本质密切相关。自1970年代起，学者已知黑洞会辐射，且辐射可能以某种方式携带落入物质被加密的信息。他们设想：若一名即将穿越古老黑洞视界的宇航员与遥远距离的观察者（收集黑洞终生辐射的人）通信会发生什么？这个思想实验的结果令人困惑：宇航员与遥远观察者将获得两份相同信息，一份来自黑洞漫长寿命中回收的辐射，另一份来自近距观测。信息重复拷贝破坏了量子力学依赖的概率精确计算。部分物理学家由此推断，视界外必然存在某种奇异现象干扰宇航员的信息收集。

短毛发与长毛发
解决信息悖论的尝试通常在事件视界外增加额外结构，即所谓量子毛发。2012年提出宇航员思想实验的研究者认为，视界外侧可能存在由高能粒子构成的"火墙"，阻断两名观察者的联系。物理学家萨米尔·马图尔则提出，黑洞根本不存在视界，而是由多种时空结构量子叠加构成的"绒毛球"，使其边缘呈现模糊态。

其他设想包括类似黑洞但被奇异物质壳包裹的"引力星"，以及不存在无限密度奇点的"规则黑洞"。

这些理论都在视界外引入新效应，势必改变振动黑洞发射引力波的方式。

此类效应通常极度接近视界，可能仅存在于10^-33厘米的普朗克长度范围内。这种极短量子毛发虽不会直接显现为黑洞碰撞信号的改变，但可能通过其他方式被观测。例如引力波在火墙或视界附近结构反射产生的异常"回声"，可能会在初始信号后出现。

目前对回声的搜寻尚无果。但失败并不排除量子毛发存在的可能性，因为尚不清楚何种量子毛发会产生回声，也不明确回声的具体表现形式。

与此同时，物理学家也在寻找更"长"的毛发——即更明显偏离爱因斯坦理论的现象。虽缺乏理论依据，但黑洞附近高度弯曲的时空对天文学家而言是新领域，可能存在未知发现。或许在这种极端条件下，时空的弯曲方式会不同于广义相对论预测。

加拿大滑铁卢大学天体物理学家尼亚耶什·阿夫肖迪认为："进行这项检验具有重要价值。"

数学与数据的交汇
自2015年激光干涉引力波天文台（LIGO）首次探测到黑洞碰撞以来，物理学家一直试图用这些数据检验爱因斯坦理论。随着欧洲Virgo与日本KAGRA观测站陆续启用，这项研究得以加速推进。但巨大的数学难题横亘在前：碰撞的黑洞始终处于旋转状态，极大增加了计算复杂度。数学家罗伊·克尔早在1963年就在爱因斯坦方程框架下计算出旋转黑洞的行为模式。但若该框架本身有误呢？

鲁汶大学物理学家团队在2023年攻克了这一难题。他们开发出新技术，用于模拟若爱因斯坦理论被修正时高速旋转黑洞的行为。

同年的一场学术会议上，鲁汶团队研究生西蒙·马诺与引力波信号分析专家、时任哥本哈根博士后研究员的格雷戈里奥·卡鲁洛相遇。他们意识到可以将鲁汶团队的理论与卡鲁洛的数据进行比对，随即展开合作。"我们当即找了张空桌开始共同编程，"现就职于伯明翰大学的卡鲁洛回忆道。

通过整合22次黑洞碰撞数据，研究者标准化了同等质量黑洞的碰撞形态，并将其与鲁汶团队的预测进行比对。这种方法使研究者能追问：若爱因斯坦理论在高度弯曲时空条件下失效，事件视界外出现火墙或绒毛球等结构，这些"毛发"的长度几何？需接近至何种距离才能发现黑洞行为偏离广义相对论预测？

以95%的置信度，他们排除了视界40公里外存在任何偏离爱因斯坦预测的现象。对多数已观测黑洞而言，这个距离略小于其自身半径。研究者远未能为黑洞实施"精修剪发"，更不用说达到检验信息悖论解决方案所需的"极致剃须"精度。但结果确实表明黑洞并未显著偏离爱因斯坦理论。

未来展望
LIGO、Virgo和KAGRA预计将持续运行至2030年代，印度新观测站约于2030年加入。更多数据将带来更精确测量。

后续，美国"宇宙探索者"与欧洲"爱因斯坦望远镜"等新一代引力波探测器将实现精度飞跃。"爱因斯坦望远镜基本上能观测宇宙中特定质量范围的所有黑洞...这令人难以置信，"卡鲁洛表示。

届时研究者将能窥探更近区域：不再是数十公里长的毛发，而是能探测足球场长度范围内对爱因斯坦理论的偏离。

"我们可能将以十万分之一的精度验证爱因斯坦广义相对论，这当然很棒，"马诺表示，"但也可能发现完全出乎意料的现象。"

英文来源：

Astrophysicists Find No ‘Hair’ on Black Holes
Introduction
According to Albert Einstein’s general theory of relativity, the behavior of a black hole depends on two numbers: how heavy it is, and how fast it is rotating. And that’s it. Black holes are said to have “no hair” — no features that distinguish them from their fellows with the same mass and spin.
With new data, it has started to become possible to test this no-hair conjecture. Astronomers have detected hundreds of signals from colliding black holes over the past 10 years. In these dramatic events, two of the invisible, inescapable pits in the fabric of space-time circle one another faster and faster, and then merge into a single, massive black hole that jiggles like Jell-O as it settles down after the collision. The merging and jiggling sends ripples called gravitational waves cascading outward through the fabric of the universe and to detectors here on Earth. If general relativity is correct, those jiggles have a cookie-cutter form that depends only on each hole’s mass and spin. (In theory, there’s a third defining property: electric charge. But real, astrophysical black holes have negligible net charge.) If the theory is wrong, astronomers might observe something new — subtle distinctions that reveal the unique history and makeup of each black hole.
“As years went by and the events piled up, we realized that we could have stronger, more robust tests of the theory [of general relativity] — or alternatives,” said Vitor Cardoso, a physicist at the Niels Bohr Institute in Copenhagen.
Cardoso and dozens of other gravitational wave astronomers recently summed up the status of those tests. Their report, released at the end of May, covers a variety of methods and results, including an analysis of gravitational wave signals conducted by Cardoso and colleagues last fall. Assembling data from multiple black hole collisions, that group found that the data agreed with Einstein’s theory as best they could tell. Any deviation from what general relativity predicts for the shape of space-time around a black hole — any “hair” — would have to lie closer to the hole than 40 kilometers.
So no hair has been seen, for now. But theorists continue to think through a multitude of possibilities, with cracks in Einstein’s theory suggesting that subtle, quantum “hair” ought to exist, even if it might be extremely challenging or even practically impossible to spot.
What Einstein Didn’t Predict
The question of hairy black holes is intimately connected to the greatest puzzle in modern physics: How can general relativity be merged with quantum theory?
Consider the situation where an object crosses a black hole’s point of no return, called the event horizon. According to general relativity, all outsiders will see is how the swallowed object contributes to the two numbers that describe the black hole: how much mass the object adds, and how much faster or slower it makes the black hole rotate.
Yet the disappearance of all other information about the engulfed object conflicts with one of the central tenets of quantum mechanics. Quantum theory requires that all information be preserved and that it remain, in theory, accessible — otherwise quantum probabilities won’t add up to 100%, as they must. Theoretical physicists have long been fascinated by this conflict between the predictions of general relativity and those of quantum mechanics, which is known as the information paradox.
In 2012, physicists showed that this paradox is tightly linked to the nature of the event horizon. They’d known since the 1970s that black holes emit radiation, and that this radiation probably somehow carries the scrambled information about the stuff that fell into the hole. Now they imagined what would happen if an astronaut who was about to cross the horizon of an ancient black hole communicated with someone far away — an observer who had gathered the radiation emitted by the black hole over its lifetime. The result of the thought experiment was puzzling: The astronaut and the faraway observer would end up with two copies of the same information, one recovered over the black hole’s long lifetime and the other from close by. The extra copy is a problem, again spoiling the careful accounting of probabilities that quantum mechanics relies on. Some physicists concluded that something strange must happen just outside the horizon to disrupt the astronaut’s information gathering.
Short Hair, Long Hair
Attempts to address the information paradox usually add extra detail outside the event horizon, referred to as quantum hair. The researchers who came up with the thought experiment about the astronauts in 2012 suggested that a shell of extremely high-energy particles called a firewall might lie just outside the horizon, breaking the connection between the two observers. Alternatively, the physicist Samir Mathur argues that black holes don’t have a horizon at all. Instead, he says that they are “fuzzballs” — each one a quantum combination, or superposition, of many different configurations of space-time, making the black hole’s edges fuzzy.
Other ideas include “gravastars” that resemble black holes but are surrounded by shells of exotic matter, and so-called regular black holes — reimagined versions of the objects that lack the infinitely dense points in their centers known as singularities.
This zoo of proposals all introduce new effects outside the horizon that should change how a vibrating black hole emits gravitational waves.
The proposed effects generally lie very close to the horizon, perhaps only within 10−33 centimeters — the so-called Planck length. Such close-cropped quantum hair would not be directly observable as a change in the signals from black hole collisions, but it might be visible in other ways. For example, unusual aftereffects called echoes, generated as gravitational waves bounce off a firewall or other structure near the horizon, might appear after an initial signal.
Searches for echoes have so far come up empty. These failed searches don’t rule out the possibility of quantum hair, however, since it’s unclear which kinds of quantum hair should give rise to echoes and which won’t, or how exactly the echoes would appear.
Meanwhile, physicists can also look for “longer” hair — more obvious deviations from Einstein’s theory. There’s less theoretical reason to expect this, but on the other hand, the highly curved space-times near black holes are a new environment for astronomers, and they can’t be sure what they might find. Perhaps space-time curves differently under these conditions than general relativity predicts.
“I think it’s a worthwhile exercise to go and test that,” said Niayesh Afshordi, an astrophysicist at the University of Waterloo in Canada.
Math Meets Data
Since the first detection of colliding black holes by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in 2015, physicists have been trying to use this data to test Einstein’s theory. The project accelerated after additional observatories — Virgo in Europe and KAGRA in Japan — came online. But a substantial mathematical challenge stood in the way: The black holes that collide are always rotating, which greatly complicates calculations. The mathematician Roy Kerr calculated back in 1963 how rotating black holes behave in the framework of Einstein’s equations. But what if that framework is wrong?
A group of physicists at KU Leuven cracked the problem in 2023. They developed a technique for understanding how fast-spinning black holes would behave if Einstein’s theory were modified.
Then, at a conference later that year, a graduate student in the Leuven group, Simon Maenaut, met Gregorio Carullo, a postdoctoral researcher in Copenhagen at the time who was an expert in analyzing gravitational wave signals. They realized that they could test the Leuven group’s theories against Carullo’s data, and they wasted no time. “We sort of jumped on a free desk and started coding together,” said Carullo, who is now at the University of Birmingham.
They combined the data from 22 black hole collisions, determining how the collisions would look if they all came from black holes of the same mass. They then compared this data against predictions from the Leuven group. The approach allowed the researchers to ask: Suppose Einstein’s theory goes wrong for highly curved space-time, and something like a firewall or a fuzzball shows up outside the event horizon. How long could that “hair” be? How close would you have to get before a black hole might behave differently than it would under general relativity?
With 95% confidence, they ruled out any deviations from Einstein’s predictions farther out from the horizon than 40 kilometers. For most of the observed black holes, that’s a bit less than the radius of the black hole itself. The researchers weren’t able to give the black holes a buzz cut by any means, let alone the close shave that most physicists expect would be necessary to test proposed solutions to the information paradox. The result does mean that black holes don’t wildly depart from Einstein’s theory.
On the Horizon
LIGO, Virgo and KAGRA are slated to run for the rest of the decade, if not longer, and will be joined by another observatory in India around 2030. More data will lead to more precise measurements.
Later, next-generation gravitational wave detectors — a planned telescope called Cosmic Explorer in the U.S., and one called the Einstein Telescope in Europe — will enable a jump in precision. “The Einstein Telescope will basically observe all the black holes in the universe of a certain mass range … which is incredible,” Carullo said.
It will then be possible to peer closer. Instead of hair a few dozen kilometers long, researchers will be able to look for violations of Einstein’s theory the length of a football field.
“It’s possible that we will confirm Einstein’s theory of general relativity to five decimal places, and that would be great,” Maenaut said, “but it’s also possible that we come across something that we didn’t expect.”