What took us so long? Only in 1998 did astronomers discover we had been missing nearly three quarters of the contents of the universe, the so-called dark energy--an unknown form of energy that surrounds each of us, tugging at us ever so slightly, holding the fate of the cosmos in its grip, but to which we are almost totally blind. Some researchers, to be sure, had anticipated that such energy existed, but even they will tell you that its detection ranks among the most revolutionary discoveries in 20th-century cosmology. Not only does dark energy appear to make up the bulk of the universe, but its existence, if it stands the test of time, will probably require the development of new theories of physics. As astronomers have explored this new phenomenon, they have found that, in addition to determining the overall expansion rate of the universe, dark energy has long-term consequences for smaller scales. As you zoom in from the entire observable universe, the first thing you notice is that matter on cosmic scales is distributed in a cobweblike pattern--a filigree of filaments, several tens of millions of light-years long, interspersed with voids of similar size. Simulations show that both matter and dark energy are needed to explain the pattern. According to models, dark matter began to clump immediately after the big bang, forming spherical blobs that astronomers refer to as "halos." The baryons, in contrast, were initially kept from clumping by their interactions with one another and with radiation. They remained in a hot, gaseous phase. As the universe expanded, this gas cooled and the baryons were able to pack themselves together. The first stars and galaxies coalesced out of this cooled gas a few hundred million years after the big bang. They did not materialize in random locations but in the centers of the dark matter halos that had already taken shape. 是什么让我们找了这么久?直到1998年，天文学家们才发现我们所说的暗能量，它几乎是宇宙能量的四分之三，在此之前一直被我们所忽视。暗能量是一种未知的能量形式，围绕在我们每个人的周围，轻轻地推拉我们，掌控宇宙的命运。但是，我们对它却几乎一无所知。确实，一些研究人员此前曾预测存在这类能量，但是他们还是会告诉你，探测暗能量是宇宙学在20世纪最具革命性的发现。暗能量可能不仅是构成宇宙的主体，而且，如果能经受住时间的检验，它将需要提出新的物理理论来支撑。 天文学家们发现这一新的现象的同时还发现，暗能量除了能决定宇宙的整体膨胀速度，还会对小规模的星系膨胀产生长久的影响。如果从整个宇宙的角度仔细观察，最先观察到的是：物质在宇宙中的排布类似于蜘蛛网的结构——数千万光年长的丝线和同样长度的真空交织而成的网状结构。仿真实验表明，要解释这一结构，既需要物质也需要暗能量。 根据模型，人们发现大爆炸后，暗物质开始迅速聚集成团，形成天文学家称为“晕”的球状团块。然而，由于重子之间的相互作用和辐射，起初它们无法聚集起来，一直处在热的气相状态。直到随着宇宙膨胀，气体冷却，重子才得以聚集。大爆炸后的数亿年，最初的各种恒星和星系脱离这一冷却气体聚集起来。它们没有随意地在其它地方成形，而是出现在已成形的暗物质晕的中心。 本文来源：https://www.wddqw.com/doc/a634afe2e2bd960591c677ad.html