What do galaxies have to do with cosmology?
|Books | Astronomy Picture of the Day | News | Calendars | Star Charts | Observing | Education|
Galaxy Birth - Accompanying those minute fluctuations in radiation, scientists believe, were tiny fluctuations of matter, or, more precisely, baryonic matter, mainly hydrogen and helium gas. Gravitational attraction between the atoms concentrated them into faint clouds of gas. As the universe expanded, the surrounding matter gradually thinned out, with the result that the internal gravity of the gas clouds grew relatively stronger. Slowly, then faster and faster, the clouds pulled in more and more material from the surrounding medium. Eventually, the clouds began to collapse under their own gravity, evolving into galaxies. About one billion years after the Big Bang, the first galaxies and the stars they contain were born.
What happened to the searchable NGC database?
Astronomy Picture of the Day: Galaxies - All the images on the APOD page are credited to the owner or institution where they originated. Some of the images are copyrighted and to use these pictures publicly or commercially one must write to the owners for permission. For the copyrighted images, the copyright owner is identified in the APOD credit line (please see the caption under the image), along with a hyperlink to the owner's location. NASA images are in the public domain, official guidelines for their use can be found here. For images credited to other owners/institutions, please contact them directly for copyright and permissions questions.
Atlas of the Andromeda Galaxy by Paul W. Hodge
Galaxy Collisions - Theories of how galaxies, the fundamental constituents of large-scale structure, form and evolve have undergone a dramatic paradigm shift in the last few decades. Earlier views were of rapid, early collapse and formation of basic structures, followed by slow evolution of the stellar populations and steady buildup of the chemical elements. Current theories emphasize hierarchical buildup via recurrent collisions and mergers, separated by long periods of relaxation and secular restructuring. Thus, collisions between galaxies are now seen as a primary process in their evolution. This article begins with a brief history; we then tour parts of the vast array of collisional forms that have been discovered to date. Many examples are provided to illustrate how detailed numerical models and multiwaveband observations have allowed the general chronological sequence of collisional morphologies to be deciphered, and how these forms are produced by the processes of tidal kinematics, hypersonic gas dynamics, collective dynamical friction and violent relaxation. Galaxy collisions may trigger the formation of a large fraction of all the stars ever formed, and play a key role in fueling active galactic nuclei. Current understanding of the processes involved is reviewed. The last decade has seen exciting new discoveries about how collisions are orchestrated by their environment, how collisional processes depend on environment, and how these environments depend on redshift or cosmological time.
The Heart of the Milky Way
© Copyright 2010 - Samuel J. Wormley