Jets in extragalactic radio sources

Observations now require that there be a continuous supply of energy to the giant extragalactic radio sources. These observations also suggest that this energy input may be in the form of streams or jets of gas emanating from the centers of galaxies and quasi-stellar objects. Current data indicate that the large-scale jet structures are not moving with relativistic speeds, as previously proposed. Slow-moving jets, which possess turbulent interiors and are dominated by relatively cool gas, can account for the observed jet properties at optical and radio wavelengths. Extremely small-scale jets observed adjacent to the central energy source may or may not be in relativistic motion.     

Numerical models of extragalactic radio sources

Numerical simulations with supercomputers allow analysis of the wide range of nonlinear physics inherent in the hydrodynamic and magnetohydrodynamic equations. When applied to extragalactic radio sources, these numerical models have begun to reproduce many of the complex structures observed on telescopic images. This combination of telescopic and numerical observations provides powerful probes of the physics of radio galaxies. In this review, some of the recent results from both two-dimensional and three-dimensional numerical simulations of the formation and evolution of extended radio morphologies are described. These numerical models have allowed the exploration of important physical phenomena including the role of magnetic fields in the dynamics and emissivity of extended radio galaxies, intermittent outflow from the cores of active galaxies, instabilities and disruption of fluid jets, and the bending of collimated outflows by motion through the intergalactic medium.     

Possibility of maser action in cosmic radio sources

A mechanism is described for maser action in synchrotron sources. The process may contribute to the lowfrequency radiation from 3C273B.     

Brightness distributions of radio sources at 2-centimeter wavelength

Maps have been made of the 2-centimeter brightness distribution of M17, Cassiopeia-A, Taurus-A, and Orion nebula with a resolution of 2.3 minutes of arc, revealing several newly resolved features. M17 is a double thermal source. Some structure appears in Cassiopeia-A, including a suggestion of a ring shape. Taurus-A exhibits a brightness map similar to that obtained in earlier low-frequency results. The central part of Orion nebula is circularly symmetric to a high degree of accuracy.     

The origin of galaxies and clusters of galaxies

Debate on how galaxies and clusters of galaxies formed has reached an interesting stage at which one can find arguments for quite different scenarios. The galaxy distribution has a complex "frothy" character that could be the fossil of a network of protoclusters or pancakes that produced galaxies. However, there are galaxies like our own that seem never to have been in a protocluster but are physically similar to the galaxies in dense clusters. Some clues to be assessed in resolving this dilemma are the possible existence of galaxy filaments, the relative ages of galaxies and clusters of galaxies, and the continuity between cluster and field galaxies and between galaxies and clusters of galaxies.     

Percolation and galaxies

A theory is presented in which much of the structure of spiral galaxies arises from a percolation phase transition that underlies the phenomenon of propagating star formation. According to this view, the appearance of spiral arms is a consequence of the differential rotation of the galaxy and the characteristic divergence of correlation lengths for continuous phase transitions. Other structural properties of spiral galaxies, such as the distribution of the gaseous components and the luminosity, arise directly from a feedback mechanism that pins the star formation rate close to the critical point of the phase transition. The approach taken in this article differs from traditional dynamical views. The argument is presented that, at least for some galaxies, morphological and other features are already fixed by general properties of phase transitions, irrespective of detailed dynamic or other considerations.     

Colliding and merging galaxies

Aided by advances in computer technology and observations from space, astronomers have begun to unravel the mysteries of galaxy formation and evolution. Galaxies evolve by interacting with their environment and especially with each other. During brief but often fierce galactic encounters, gravitational forces generate strong tides that survive as telltale signatures for billions of years. Because these so-called collisions dissipate orbital energy, galaxies on bound orbits may eventually merge. Collisions and mergers are responsible for a great variety of phenomena, including the triggering of widespread star formation in galaxies and the fueling of nuclear activity in quasars. Evidence is accumulating that not all galaxies formed shortly after the Big Bang. A sizable fraction of them may have formed later, and many are still experiencing significant dynamical evolution.     

Discovery of new variable radio sources in the nucleus of the nearby galaxy messier 82

Widespread variability has been discovered in a large population of radio sources close to the nucleus of an active galaxy. The galaxy, Messier 82 (M82), and others similar to it show evidence for enhanced nuclear activity and unusually strong far-infrared emission. The observational data, obtained with the National Radio Astronomy Observatory's Very Large Array in New Mexico over the past 3 years, provide the first direct "look" at a starburst-the phenomenon of sudden, rapid star formation which occurs near the nucleus of a small fraction of galaxies. Nearly all the brightest of about 40 radio sources in M82' s nucleus decreased in intensity over 2.7 years up to October 1983. One source, which in February 1981 was ten times as bright as our Galaxy's most luminous supernova remnant, turned off within only a few months. Most of the other ten strongest sources are declining so rapidly that they will fade into the background within 30 years. Thus, new supernovae are expected to appear in M82' s nucleus every few years. The discovery has revealed the "engine room" of the mysterious activity in M82 and, by implication, similar active galaxies which have disturbed nuclei and which are unusually luminous in the far infrared. An estimate of the rate of energy input by the radio-visible supernovae closely matches the far-infrared luminosities which were recently measured for M82 and other similar galaxies.     

几种特异小麦的醇溶蛋白电泳分析

应用酸性聚丙烯酰胺凝胶电泳 (APAGE)对 4份波兰小麦、2份新疆稻麦、1份硬粒小麦和 1份矮兰麦进行了醇溶蛋白电泳分析 ,结果表明 :①波兰小麦具有明显的醇溶蛋白多态性 (多样性 ) ,其中的矮秆波兰小麦的谱带与产于新疆吐鲁番的波兰小麦极为相似 ;②波兰小麦与硬粒小麦、矮兰麦的α -醇溶蛋白和ω -醇溶蛋白的区别较明显。硬粒小麦和矮兰麦在α区域的带纹明显较波兰小麦多 ;③波兰小麦与新疆稻麦的醇溶蛋白电泳图谱具有一定的相似性 ,产于新疆和田的波兰小麦与新疆稻麦的共同醇溶蛋白带纹达到 6 2 5 % ,表明新疆稻麦与波兰小麦具有较近的亲缘关系 ,从醇溶蛋白方面证明了新疆稻麦起源于波兰小麦的可能性。