Today, tomorrow, learn English naturally. 天天自然学英语
The James Webb Space Telescope discovers enormous distant galaxies that should not exist
Giant, mature galaxies seem to have filled the universe shortly after the Big Bang, and astronomers are puzzled.
Nobody expected them. They were not supposed to be there. And now, nobody can explain how they had formed.
Galaxies nearly as massive as the Milky Way and full of mature red stars seem to be dispersed in deep field images obtained by the James Webb Space Telescope (Webb or JWST) during its early observation campaign, and they are giving astronomers a headache.
These galaxies, described in a new study based on Webb's first data release, are so far away that they appear only as tiny reddish dots to the powerful telescope. By analyzing the light emitted by these galaxies, astronomers established that they were viewing them in our universe's infancy only 500 to 700 million years after the Big Bang.
Such early galaxies are not in themselves surprising. Astronomers expected that first star clusters sprung up shortly after the universe moved out of the so-called dark ages — the first 400 million years of its existence when only a thick fog of hydrogen atoms permeated space.
But the galaxies found in the Webb images appeared shockingly big, and the stars in them too old. The new findings are in conflict with existing ideas of how the universe looked and evolved in its early years, and don't match earlier observations made by Webb's less powerful predecessor, the Hubble Space Telescope.
"We had specific expectations for the type of galaxies that live in the early universe: they are young and small," Joel Leja, assistant professor of astronomy and astrophysics at Penn State and one of the authors of the study, told Space.com in an email. "Previous studies of the early universe with Hubble and other instruments tend to find small, blue, baby galaxies at early times: objects which have just recently formed out of the primordial cosmic soup and are themselves building their early stars and structures."
Young stars in general shine bright blue. With age, stars develop a redder glow as they burn through their fuel and cool down. In ancient galaxies that Webb was built to spot, astronomers had not expected to see old red stars. They also had not expected to find galaxies more massive than perhaps a billion suns. But those reddish dots revealed in Webb's deep fields appear 50 times more massive than that, Leja said.
"The most massive galaxies in our sample are estimated to have masses [two to four times lower] than that of our own Milky Way," Leja wrote. "This was astounding — we're finding galaxy candidates as massive as our own galaxy when the universe was 3% of its current age."
Leja said that before astronomers start rewriting cosmology theories to explain how these galaxies came together so quickly after the Big Bang, they will have to ensure the odd red dots they are looking at are not something else. Most of the alternative explanations, however, also require entirely new concepts, Leja said.
"For example, stars in the early universe might emit light in exotic ways due to their lack of heavy elements, and perhaps we're not incorporating those in our models," Leja wrote. "Or alternatively, perhaps our understanding of how stars form locally, e.g. how many stars form from gas as a function of the mass of the stars, is totally inapplicable in the early universe. These things would also be exciting to discover and would also overturn our understanding of star formation in the early universe — just in a very different way."
The images that revealed these puzzling galaxies were obtained by Webb's Near Infrared Camera (NIRCam) as part of the Cosmic Evolution Early Release Science (CEERS) program. Astronomers plan to soon turn Webb's mirror to these galaxies again to, this time, obtain light spectra of those distant dots. Spectra break down the observed light according to its wavelength composition and thus reveal the chemical and physical properties of its source.
"The most important thing is that spectra give very precise distances to these objects," said Leja. "The "distance" and the "identity" of these objects is correlated: if we know the distance, we can pin down the identity, and vice versa. So a spectrum will pretty immediately tell us if our hypotheses are correct."
Only a little more than six months after the Webb team released the first observations from the grand observatory, scientists are already challenged to rewrite their theories about the early universe.
"We looked into the very early universe for the first time and had no idea what we were going to find," Leja said in a Penn University statement.(opens in new tab) "It turns out we found something so unexpected it actually creates problems for science. It calls the whole picture of early galaxy formation into question."
注释：
disperse: v
表示“ 分散 ”，means "(cause to) go in different directions; scatter; break up “，如：The police dispersed the crowd. 警方驱散群众。
astronomer：n
表示“ 天文学家 ”，means "a physicist who studies astronomy “，如：He wished to be an astronomer when he was a child. 他还是孩子的时候就梦想成为天文学家。
infancy：n
表示“ 婴儿期 ”，means "the early stage of growth or development “，如：Children are in their infancy when they are babies. 孩子们还是小宝宝时，是处于婴儿期。
permeate：v
表示“渗透 ”，means " pass through or into every part of “，如：His subtle satisfaction seemed to permeate the space around them. 他难以捉摸的满足感好像弥漫在了他们的周围。
Astrophysics：n
表示“ 天体物理学 ”，means "the branch of astronomy concerned with the physical and chemical properties of celestial bodies “，如：He is using theories on the frontier of astrophysics. 他在运用关于天体物理学新领域的理论。
Hubble：n
表示“ 哈勃(姓氏）”，这里引申指“哈勃望远镜 ”，如：Right from the start there was trouble with the Hubble. 从最开始哈勃望远镜就有问题。
Primordial：adj
表示“ 原始的”，means "having existed from the beginning; in an earliest or original stage or state “，如：It is the primordial force that propels us forward. 它是推动我们前进的原始动力。
candidate: n
表示“候补者 ”，means "someone who is considered for something “，如：This candidate does not meet the requirement that secondary school should be completed. 这位考生没有达到中学毕业的要求。
exotic：adj
表示“奇异的 ”，means " striking or attractive“，如：Some turned their hats into more exotic shapes. 个别人戴的帽子怪模怪样。
spectra：n
表示“ 光谱 ”，如：They could look at the spectra of the light the moons reflected. 他们可以观察月亮反射的光的光谱.
pin：v
表示“钉住；别住 ”，means " fasten or join with a pin or pins“，如：He pinned the notice to the board. 他把通知钉在布告牌上。
中文简要说明：
詹姆斯•韦伯太空望远镜（JWST）令天文学家头痛了！它所拍摄的宇宙最早期照片，严重冲击现有的宇宙学理论，应验了科学界的一句俗话「所知愈多，问题反而更多」。
根据现有理论，宇宙的年龄大约是137亿年，而一个巨大的成熟星系，至少需要几十亿年的演化才会形成。然而韦伯望远镜所拍摄到的深远宇宙，却已经充满各种成熟星系，其中不乏许多中老年恒星，天文学家大叹「它们不应该在那里。」
令天文学家困惑的“元凶”，是韦伯回传的第一份深太空照片，由于那些星系距离非常远，以至于即使是韦伯如此强大的红外线望远镜，看起来也只是微小的红点。通过分析这些星系发出的光，天文学家确定，这些小红点是宇宙大爆炸（Big Bang）后5至7亿年的宇宙早期。
这时期有星系并不令人惊讶。依现有天文学理论，在「大霹雳」之后，宇宙快速扩张，但这时还没有任何星星，因为此时宇宙间只有浓厚的氢原子雾，它们还在找机会凝结。这个无星光的时期，就被称为「宇宙的黑暗时代」，它的时间大约是4亿年，之后第一批恒星如雨后春笋般涌现，也开始形成星系。
仅有4亿年的恒星，应该是相当狂暴，早期星系可能还不规则。但韦伯所发现的星系实在大得惊人，其中的恒星也太成熟了，这与现有理论明显冲突，甚至不符合早期观察。
宾州大学天文学家莱哈（Joel Leja）说：「我们对早期宇宙星系的推测是，它们应该年轻而且体积小。以前哈伯望远镜和其他仪器的观测数据，也是小型而且蓝色恒星为主的婴儿星系。」
然而，韦伯拍摄的超早期星系却有古老的红色恒星，而且星系的规模与银河系相若，「这就有点像，一个实际年龄3岁的孩子，已经180公分高，而且长了胡子」。莱哈表示，目前还没有答案，只能提出各种猜想；然而，猜想也就意味着需要新的理论。莱哈说：「如果要我勉强猜测，我会想早期恒星与现行恒星有什么根本上的差别。例如，早期恒星必然缺乏重元素，可能会以奇特的方式发光，目前我们还没有考虑到这一部分。又或者，最早期恒星的形成方式，可能与后来的次生恒星有根本上的差异。」
韦伯望远镜是2021年12月25日发射的，2022年7月正式工作。它仅用半年观测，就几乎要打翻天文学理论。科学家虽然感到头痛，但仍然很高兴，这意味着有更多的问题值得研究。
留言微信公众号《自然学英语LearnNaturally》，可咨询更多：