宇宙中恒星的演化始于巨星的形成,后者的质量是太阳系的数百倍,寿命估计为数百万年.重元素合成于巨星的内部.它们控制了巨星爆炸过程中( 超新星)形成的气态云和盘状物的冷凝加速度.冷凝和旋转的加速导致后代恒星质量越来越小,寿命越来越长,直到形成像太阳这样的小星体,其质量为1.989×1030kg,寿命已有几十亿年.这些小恒星的形成是冷凝过程中产生的水成冰氢星子不断聚集的结果.上一代巨星的原始星盘中的物质只有一小部分参与了冰氢星子的形成.这些星体形成于致密、高速旋转的原始恒星星盘中,周围环绕着巨行星和褐矮星.由于星体达到恒星状态,它们开始影响原恒星盘,结果导致星体相互分散,同时,最近的巨星发生表面去气作用.后者可以从巨星到恒星的质量衰减得到证实 .Upsilon Andromedae、55Cancri和HD168443等天体的巨行星记载了这样的事实.太阳系中的表面去气作用主要反映在近太阳巨星的流体外壳完全消失.由于流体外壳消失,铁-硅酸盐熔融核暴露地表,形成小的类地行星.木星也经历过表面去气作用,依据是木星具有很高的平均密度(1.3g/cm3),几乎是土星密度(0.7g/cm3)的两倍.因此,类地行星的形成经历了两个阶段:原行星(其父巨星具有重的熔融核)和正常行星(在其父行星失去流体外壳之后形成).由于离心力的作用,从流体外壳分离出来的熔融体成为巨星的卫星.类地行星在失去流体外壳的同时也失去了它们的卫星(只有月球、火卫一和火卫二例外).原地球是地球的父行星,铁-硅酸盐熔融核和月球在离心力的影响下已从其流体外壳分离出来.%The stellar evolution of the Universe has started from the formation of giant stars, the masses of which are hundreds times larger than the solar mass, and their lifetime has been estimated as millions years. Heavy elements have been synthesized in the interiors of giant stars. They have controlled the acceleration of cooling in gaseous clouds and disks being formed in the course of their explosions (supernova). The acceleration of cooling and rotation resulted in the decrease of stellar masses of next generations and increase of their lifetime up to the formation of small stars similar to the Sun (its mass is 1.989×1030kg) with a lifetime of billions years. They have been formed as a result of accretion of aqueoushydrogen icy planetesimals resulted from cooling. Only a small part of mass of protostellar disks that have appeared from giant stars of previous generation has managed to compose them.These stars have been formed in dense rapidly rotating protostellar disks together with surrounding giant planets and brown dwarfs. As the stars have reached the stellar state, they have influenced on protostellar disk resulting in its dissipation, and the nearest giants have undergone surface degassing. The latter is reflected by the decrease of mass of giants down to stars. It has been registered for giant planets of the Upsilon Andromedae, 55 Cancri, and HD 168443 stars. Surface degassing in the solar system has been mainly reflected by the complete loss of fluid envelopes by near-solar giants. Their iron-silicate molten cores have been exposed forming small terrestrial planets. Jupiter has also undergone surface degassing, as it is evident from its high average density (1.3 g/cm3), that is almost twice higher than that of Saturn (0.7 g/cm3). Thus terrestrial planets has been formed in two stages: protoplanetary (as heavy molten cores of their parent giants) and proper planetary (after the loss of fluid envelopes by parent planets). Satellites of giants have been separated as molten bodies from their giant fluid envelopes under the influence of centrifugal forces. Terrestrial planets have lost their satellites with the loss of fluid envelopes (only the Moon, Phobos and Deimos have remained). ProtoEarth is the parent planet for the Earth formed as iron-silicate molten core and the Moon separated from its fluid envelope under the influence of centrifugal force.
展开▼
