The James Webb Telescope Is Changing Astronomers’ Understanding of the Ancient Cosmos
The James Webb Telescope Is Changing Astronomers’ Understanding of the Ancient Cosmos
詹姆斯·韦伯望远镜正在改变天文学家对古老宇宙的认知
When Charlotte Mason ponders cosmic mysteries, she likes to doodle. “I am quite a visual person,” she said. “I usually draw a lot of pictures trying to understand what’s going on.” 当夏洛特·梅森（Charlotte Mason）思考宇宙奥秘时，她喜欢涂鸦。“我是一个非常注重视觉的人，”她说，“我通常会画很多图来尝试理解正在发生的事情。”
Mason, an astrophysicist at the Cosmic Dawn Center in Copenhagen, has lately been filling pages with sketches of “little red dots,” perplexing objects discovered by the hundreds in images from the James Webb Space Telescope (JWST). Little red dots were never seen before the telescope came online in 2022. But we now know that they started to appear in significant numbers roughly 650 million years after the Big Bang. 梅森是哥本哈根宇宙黎明中心（Cosmic Dawn Center）的一位天体物理学家，最近她一直在纸上画着“小红点”的草图。这些令人困惑的天体在詹姆斯·韦伯空间望远镜（JWST）拍摄的图像中被发现了数百个。在2022年该望远镜投入使用之前，人们从未见过这些小红点。但我们现在知道，它们在大爆炸后约6.5亿年开始大量出现。
These dots are just one of the thrilling mysteries that have emerged from JWST’s observations of the early universe. Others include black holes that seem impossibly large for their age, as well as ancient galaxies that defy what we thought we knew about the first billion years after the Big Bang. At first, scientists were astounded: The universe revealed by JWST simply didn’t square with our understanding of astrophysics. Now, a wave of new theories offers tantalizing solutions—but which ones portray reality is an open question. 这些小红点只是JWST对早期宇宙观测中涌现出的众多激动人心的谜团之一。其他谜团还包括那些相对于其年龄而言大得不可思议的黑洞，以及挑战了我们对大爆炸后最初十亿年认知的古老星系。起初，科学家们感到震惊：JWST所揭示的宇宙与我们对天体物理学的理解完全不符。现在，一波新的理论提供了诱人的解决方案，但究竟哪一种理论描述了现实，仍是一个悬而未决的问题。
Recent ideas suggest that little red dots could be black holes cocooned in thick gas, possibly representing a completely new type of object called a black hole star, in which the tight shroud of gas emits light like a stellar atmosphere. 近期的观点认为，小红点可能是被浓厚气体包裹的黑洞，这可能代表了一种全新的天体类型，被称为“黑洞星”（black hole star），在这种天体中，紧密的气体外壳像恒星大气一样发光。
“This would be my black hole,” Mason said, drawing a small circle and filling it in. “I might put a disk on it, because we think that’s where some of the emission comes from.” She slashed a line through the circle’s center. “Then the kind of naïve picture is just this dense gas cloud around the black hole.” She drew a larger circle surrounding the object. “这就是我的黑洞，”梅森一边说，一边画了一个小圆圈并将其涂满。“我可能会在它上面加一个圆盘，因为我们认为部分辐射就来自那里。”她在圆圈中心画了一条斜线。“那么，一种比较天真的构想就是黑洞周围包裹着浓密的气体云。”她在物体周围画了一个更大的圆圈。
But Mason thinks there may be more to these cosmic enigmas. She and colleagues recently analyzed the spectrum of light emitted by one little red dot. If the dense-cloud picture is correct, then some of the light should have been altered from passing through the gas—but that’s not what they saw. 但梅森认为这些宇宙谜团可能远不止于此。她和同事最近分析了一个小红点发出的光谱。如果“浓密气体云”的构想是正确的，那么部分光线在穿过气体时应该会发生改变，但他们观察到的情况并非如此。
“Now what do I do? Start again. But now if I make my gas clumpy,” Mason said, drawing a new diagram with holes in the clouds surrounding the black hole, “I should be able to get [a signal] that looks closer.” “现在我该怎么办？重新开始。但如果我让气体变得不均匀（结块），”梅森一边说，一边画了一张新图，在黑洞周围的云层中画出了一些空隙，“我就应该能得到看起来更接近（实际信号）的结果。”
All around the world, researchers like Mason are eagerly piecing together JWST’s glimpses of the ancient cosmos to create a clearer picture of our universe’s beginnings. And like the photons that travel billions of light-years to reach us, new fragments are constantly falling into place. 在世界各地，像梅森这样的研究人员正热切地将JWST对古老宇宙的观测片段拼凑在一起，以勾勒出我们宇宙起源的更清晰图景。就像那些穿越数十亿光年来到我们身边的光子一样，新的拼图碎片正在不断归位。
The Universe’s Bottomless Pits
宇宙的无底洞
The story of black holes has become more complicated thanks to JWST, which keeps spotting ancient black holes that are too big to explain with established theories—much too big. 多亏了JWST，黑洞的故事变得更加复杂了。它不断发现一些古老的黑洞，这些黑洞大到无法用现有理论来解释——实在太大了。
Shortly after the Big Bang, the universe was largely featureless and smooth. Then, just a few hundred million years later, “we already see billion-sun black holes growing,” said Jenny Greene, an astrophysicist at Princeton University. “In order to get them that big so quickly, you have to do some gymnastics.” 在大爆炸后不久，宇宙基本上是平滑且没有特征的。然而，仅仅几亿年后，“我们就已经看到了质量达到十亿倍太阳质量的黑洞在生长，”普林斯顿大学的天体物理学家珍妮·格林（Jenny Greene）说，“为了让它们在如此短的时间内长得这么大，你必须进行一些‘体操式’的推演。”
Scientists look at two key factors that influence a black hole’s size: how massive a black hole “seed” was when it originated, and how quickly these seeds grew after that. But it’s hard to explain how black holes either formed already big enough or grew fast enough to reach a billion times the mass of the sun in early cosmic times. 科学家们关注影响黑洞大小的两个关键因素：黑洞“种子”起源时的质量，以及这些种子在此后的生长速度。但很难解释黑洞是如何在宇宙早期就形成得足够大，或者生长得足够快，从而达到太阳质量的十亿倍。
In the modern universe, black holes form when the core of a massive star runs out of fuel and collapses. Considering the first stars were quite massive, they could have left behind black hole seeds of up to about 100 solar masses, Greene said. 在现代宇宙中，黑洞形成于大质量恒星核心燃料耗尽并坍缩之时。格林表示，考虑到第一代恒星质量相当大，它们可能留下了质量约为100倍太阳质量的黑洞种子。
“We know that happens, but it’s really, really hard to get them to a billion so quickly,” she said. “You really have to force-feed them.” “我们知道这种情况会发生，但要让它们如此迅速地增长到十亿倍太阳质量真的非常、非常困难，”她说，“你必须强行‘喂养’它们。”
Scientists have historically believed there’s a hard limit to how fast black holes can grow. As material falls toward the black hole, it gets hot as it spins around like water going down a drain. The radiation that this “accretion disk” produces pushes back against more stuff flying in, preventing the black hole from consuming more. This intake limit, called the Eddington limit, should make it impossible for black holes to grow tens of millions of times larger in the time available. 科学家们历来认为黑洞的生长速度存在一个硬性上限。当物质落向黑洞时，它会像水流进下水道一样旋转并变热。这种“吸积盘”产生的辐射会向外推挤更多涌入的物质，从而阻止黑洞吞噬更多东西。这种摄入限制被称为“爱丁顿极限”（Eddington limit），它理应使得黑洞不可能在现有的时间内增长到数千万倍大。
But recent computer simulations suggest that black holes might have something of a back door. If the accretion disk puffs up in just the right way, the incoming gas can overwhelm the radiation pressure. Such “super-Eddington” accretion would lead to gas funneling in at extraordinary rates. 但最近的计算机模拟表明，黑洞可能拥有一种“后门”。如果吸积盘以恰当的方式膨胀，涌入的气体就能压倒辐射压力。这种“超爱丁顿”吸积会导致气体以惊人的速度汇入。
Even so, astronomers don’t know if there would have been enough gas around to produce the biggest black holes. Some researchers think that ancient, dense star clusters may have created lots of black hole seeds that rapidly merged. 即便如此，天文学家仍不确定当时是否有足够的气体来产生最大的黑洞。一些研究人员认为，古老而密集的星团可能产生了大量的黑洞种子，并迅速合并。
Or perhaps supermassive black holes never started as stars at all. In this case, colossal clouds of gas would have plunged directly into a black hole. This “direct collapse” mechanism can form a seed some 10,000 times the mass of the sun. 又或者，超大质量黑洞根本不是从恒星开始的。在这种情况下，巨大的气体云可能直接坍缩成了黑洞。这种“直接坍缩”机制可以形成一个质量约为太阳1万倍的种子。
“The problem with the direct-collapse picture is that it requires really Goldilocks conditions,” Greene said. For direct collapse to work, a gargantuan cloud needs to compress into a black hole all at once, without first fracturing into smaller clouds that would form stars. This requires specific gas chemistries, and the cloud must rotate slowly. “直接坍缩构想的问题在于，它需要非常苛刻的‘金发姑娘条件’（即恰到好处的条件），”格林说。要实现直接坍缩，巨大的气体云需要一次性压缩成黑洞，而不能先分裂成形成恒星的小云团。这需要特定的气体化学成分，且云团必须缓慢旋转。
“When people try to do this in a computer, they can make these direct-collapse black holes, but they can’t make enough of them to explain all the black holes that we see,” Greene said. “当人们尝试在计算机中模拟时，他们可以制造出这些直接坍缩的黑洞，但无法制造出足够多的数量来解释我们所看到的所有黑洞，”格林说。
There’s some evidence to support each of these theories. In 2024, JWST saw a black hole from about 1.5 billion years after the Big Bang gobbling up material at about 40 times the Eddington limit. If black holes earlier in cosmic time also stuffed themselves… 目前有一些证据支持上述每一种理论。2024年，JWST观测到一个大爆炸后约15亿年的黑洞，它正以约40倍爱丁顿极限的速度吞噬物质。如果宇宙早期更古老的黑洞也这样“暴饮暴食”……