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JWST finds oldest black hole ever seen, and it’s hungry
Within GN-z11, a galaxy in the constellation Ursa Major, astrophysicists have discovered the oldest black hole, weighing in at a few million times the mass of the Sun. It lives at the galaxy’s center and is wolfing down matter at a time more than 13 billion years ago, or just 400 million years after the Big Bang.
The James Webb Space Telescope (JWST) spotted signs of the black hole’s glowing accretion disk with NIRCam, the telescope’s primary camera. The find highlights one of the biggest unanswered questions in astronomy: How the first black holes formed at all.
The observation was published Jan. 17 in the journal Nature.
Origin story
Based on what we know about black holes, one this massive would have taken billions of years to form — much longer than its current age.
One way it could reach this size is by eating away at its surroundings much faster than the predicted rate.
Accreting black holes grow by pulling material such as dust and gas in. This infalling matter creates a bright, glowing disk. Our instruments can detect the glowing disk, which we see in the famous first image of a black hole, M87, as well as the image of the Milky Way’s supermassinve black hole, both taken with the Event Horizon Telescope.
GN-z11, one of the first galaxies formed, is smaller than our Milky Way Galaxy. Nonetheless, “very early galaxies were extremely gas-rich, so they would have been like a buffet for black holes,” said Roberto Maiolino, study lead author at the University of Cambridge, in a statement.
So, there’s plenty of food to feed a growing supermassive black hole. But there is a limit to how fast a black hole can eat, called the Eddington rate. If it tries to eat even quicker, the accretion disk heats to the point where it forms a wind of energetic particles. Therefore, the black hole begins to blow away its glowing disk, limiting its growth.
This wind can have effects far beyond the black hole as well. The wind can heat the interstellar gas throughout its host galaxy, which becomes too warm to condense and form stars, putting a stop to star formation within the host.
In some cases, though, a black hole can exceed the Eddington rate without losing its disk. This is called super-Eddington accretion, and it’s exactly what seems to be going on within GN-z11. Its black hole is eating at five times the Eddington rate, potentially confirming one of the theories for growing a big black hole: that they can temporarily exceed the Eddington rate, going through short episodes of super-Eddington accretion before calming down again.
Elusive answers
Episodes of super-Eddington accretion is only one way that such young supermassive black holes could grow. Alternative theories suggest that massive black holes could form essentially “instantaneously” when large clouds of primordial gas in the early universe collapse directly into massive black holes. And even though GN-z11’s black hole is currently accreting at a high rate, researchers can’t determine whether it started as a lower-mass black hole or one of the massive ones created through direct collapse.
Using JWST, experts are hoping to find even older black holes. And with each new black hole they find, researchers can further piece together the way such black holes are born, finally answering the question of whether they start off already massive or if they consume their way to the top.
注释：
accretion: n
表示"生长；增加"，means "an increase by natural growth or addition"，如：The fund was increased by the accretion of new shareholders. 随着新股民的增加，基金上涨了。
infalling: adj
表示"落下的"，如：As the infalling matter approached the center, it reached higher and higher densities. 当坠入的物质接近中心时，它的密度会越来越高。
primordial: adj
表示" 原始的；"，means "having existed from the beginning"，如：It is the primordial force that propels us forward. 它是推动我们前进的原始动力。
中文简要说明：
韦伯太空望远镜（JWST）发现有史以来所观测到最古老的黑洞，距今有130亿年的历史，仅约在大爆炸后4年亿年诞生，而且他比吞噬物质的速度比预期还要快，这样现象为天文学家开了一扇窗，为大型黑洞的如何增长的理论提供了一些关键信息。
据《天文学》（Astronomy）报导，天文学家在大熊座 （Ursa Major）的星系GN-z11中，发现了目前已知最古老的黑洞，其质量约为太阳的数百万倍。它位于该星系（Galaxy）的中心，于大约130亿年前，即大爆炸后4亿年，开始吞噬物质。韦伯太空望远镜（JWST）发现了黑洞发光的吸积盘的迹象，这一发现突显了天文学中一个最大的未解之谜，即第一个黑洞到底是如何形成的。目前这一次的观测结果已于近日发表在《自然》（Nature）期刊上。
GN-z11是最早形成的星系之一，它比我们的银河系小。剑桥大学的研究主持人马约里诺（Roberto Maiolino）表示「非常早期的星系富含大量气体，所以它们对黑洞来说简直就像是自助餐？」因此，有足够的食物来养活一个不断增长的超大质量黑洞。
但是，黑洞吞噬的速度是有限的，被称为爱丁顿亮度又称爱丁顿极限（Eddington limit）。如果黑洞尝试更快地吞噬物质，那么吸积盘会加热到形成高能粒子的强风。如此一来，黑洞将会吹走自己的吸积盘（上面的物质）然后吞噬不到新的物质，限制自己的增长。
这样的「强风」还会在黑洞之外产生深远的影响，会使星系内的星际气体升温，变得太温暖而无法凝聚形成恒星，从而抑制了星系内的恒星形成。
不过在某些情况下，黑洞可以超越爱丁顿极限，又不失去吸积盘。这被称为超艾丁顿吸积（super-Eddington accretion），这似乎正是在GN-z11中正在发生的事情。
那个古老的黑洞正以5倍的爱丁顿极限吞噬物质，这可能让天文学家确认了一一种大型黑洞增长的理论：它们可以暂时超越爱丁顿极限，经历短暂的超艾丁顿吸积阶段后，然后再次冷静下来。
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