The Universe Is Full of ‘Impossible’ Black Holes. Now Scientists Know Why

宇宙中充满了“不可能”的黑洞，科学家终于找到了原因

An international team of astrophysicists has found evidence that the universe recycles black holes, merging them to form even larger ones. Gravitational waves recorded in recent years show that some of the heaviest black holes within star clusters exhibit clear signs of being “second-generation” black holes—products of past collisions—and therefore could not have originated from the collapse of a massive star. 一个国际天体物理学家团队发现证据表明，宇宙会“回收”黑洞，将它们合并成更大的黑洞。近年来记录的引力波显示，星团中一些最重的黑洞表现出明显的“第二代”黑洞特征——即过去碰撞的产物——因此它们不可能是由大质量恒星坍缩形成的。

Impossible Black Holes

“不可能”的黑洞

The evolutionary theory of stars explains that, at the end of the lives of the most massive stars, their cores compress until they form a point so dense that it curves space-time to infinity. This is the classic black hole, with masses 10 to 40 times that of the sun. There are also supermassive black holes, in the center of galaxies, with millions or billions of solar masses, whose origin is related to processes that occurred in the earliest moments of the universe. 恒星演化理论解释说，当大质量恒星生命终结时，其核心会压缩到一个极度致密的点，导致时空无限弯曲。这就是经典的黑洞，其质量为太阳的 10 到 40 倍。此外，星系中心还存在超大质量黑洞，其质量可达数百万甚至数十亿倍太阳质量，它们的起源与宇宙诞生初期的过程有关。

Between these two extremes lies a contested category: black holes with masses between 40 and 100 solar masses. They are too heavy to be born after the death of a star, but they do not reach the necessary dimensions to emerge from the collapse of a gigantic cloud of matter. Conventional stellar physics considers them “impossible,” yet they appear frequently in detections. 在这两个极端之间存在一个备受争议的类别：质量在 40 到 100 倍太阳质量之间的黑洞。它们太重了，不可能是恒星死亡后的产物，但又没有达到由巨大物质云坍缩形成所需的规模。传统的恒星物理学认为它们是“不可能”存在的，但它们却频繁出现在探测结果中。

A “normal” sized black hole, isolated in space. Courtesy of Space Telescope Science Institute Office of Public Outreach 一个处于太空孤立状态的“正常”大小黑洞。图片来源：太空望远镜科学研究所公共外联办公室

Astrophysicists propose that these massive black holes could form by the merging of two or more smaller, ultradense objects. The idea was plausible, but it needed evidence. Until relatively recently, there was no way to obtain it. 天体物理学家提出，这些巨大的黑洞可能是由两个或多个较小的超致密天体合并而成的。这个想法虽然合理，但需要证据支持。直到最近，我们才有了获取这些证据的方法。

Then gravitational wave detectors came on the scene. These instruments use lasers to measure the micro-distortion of space-time generated by the collision of extremely dense objects. The first detection, in 2015, confirmed a merger between black holes. Since then, each new signal has allowed for a better characterization of these structures and revealed that these collisions occur much more frequently than previously imagined. 随后，引力波探测器登场了。这些仪器利用激光测量由极高密度天体碰撞产生的时空微小畸变。2015 年的首次探测证实了黑洞之间的合并。从那时起，每一个新的信号都让我们能更好地描述这些结构，并揭示出这些碰撞发生的频率远比之前想象的要高。

The Second-Generation Signature

“第二代”特征

The study, published this month in Nature Astronomy, analyzed a transient catalog of gravitational waves generated by the world’s three leading observatories. The database included 153 reliable detections of black hole mergers. Among them, 34 corresponded to particularly heavy objects. 本月发表在《自然-天文学》上的一项研究，分析了全球三大领先天文台产生的引力波瞬态目录。该数据库包含了 153 次可靠的黑洞合并探测记录。其中，有 34 次涉及特别巨大的天体。

By comparing all the signals, the team identified two distinct populations. The lighter black holes, up to about 40 solar masses, showed small, aligned spins, as expected for objects born from the collapse of a star. But from a certain point, around 45 solar masses, a completely different population appeared: heavier black holes, spinning rapidly and in chaotic directions—a statistical signature that can arise only when the object has already participated in a previous merger. 通过对比所有信号，研究团队识别出了两个截然不同的群体。较轻的黑洞（最高约 40 倍太阳质量）表现出较小且对齐的自旋，这符合恒星坍缩产生的天体特征。但从约 45 倍太阳质量开始，出现了一个完全不同的群体：更重的黑洞，它们自旋极快且方向混乱——这是一种统计学特征，只有当该天体已经参与过之前的合并时才会出现。

“This is the exact signature you would expect if black holes repeatedly merged into dense stellar clusters,” said Isobel M. Romero-Shaw, coauthor of the research, in a statement from Cardiff University. “如果黑洞在致密星团中反复合并，这正是你所预期的特征，”该研究的合著者、来自卡迪夫大学的伊莎贝尔·M·罗梅罗-肖（Isobel M. Romero-Shaw）在一份声明中表示。

So far researchers have not directly observed any of these “impossible” black holes. They do not appear in x-rays or in the visible spectrum, unlike supermassive ones. However, their collisions vibrate space-time, and that vibration reveals masses that stellar physics cannot explain. 到目前为止，研究人员还没有直接观测到这些“不可能”的黑洞。与超大质量黑洞不同，它们不会在 X 射线或可见光谱中显现。然而，它们的碰撞会引起时空震动，而这种震动揭示了恒星物理学无法解释的质量。

This study shows that the heaviest black holes are built rather than born. They arise from previous generations of collisions, assembled in the densest environments in the cosmos. 这项研究表明，最重的黑洞是“建造”出来的，而非“诞生”的。它们源于前几代的碰撞，是在宇宙中最致密的环境中组装而成的。

This story originally appeared in WIRED en Español and has been translated from Spanish. 本文最初发表于《连线》西班牙语版，由西班牙语翻译而来。