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Free Wallpapers Sky, Galaxies & Space Page 8
All free wallpaper images of space, galaxies, the solar system, stars, planets including Hubble Telescope and NASA pictures. See both Space Wallpaper categories below for all image downloads.
Home > Free Wallpapers > Sky, Galaxies & Space Wallpapers
Free Wallpaper Images - The Sky, Galaxies and Space
Sky, Galaxies & Space Wallpaper Downloads - Viewing Page 8
Huge selection of high resolution desktop wallpapers from NASA, the Hubble Telescope and other invaluable sources. Our night sky, the nine planets in our solar system, the earth, sun, mars, jupiter, venus, uranus, pluto, saturn, mercury, stars, star births, star formaions, distant galaxies, nebula (nebulae) and many more stunningly beautiful pictures of our solar system and beyond. Find high quality wallpaper pictures for your computer desktop and download free.
How to Download Your Free Computer Wallpapers
Right-click on a wallpaper preview pane and choose 'Save Picture As' or 'Save Image As' to save it on your computer in full size. To preview any wallpaper image at full size, click on a wallpaper preview picture or the link describing the wallpaper. All wallpaper images are minimum 1024 x 768 for great viewing on any desktop.
Index of Free Space Wallpaper Downloads
Sky, Outer Space, Galaxies, Solar System, Space, Planets and Stars
Sky, Galaxies & Space Planets, Stars & Solar System
1 2 3 4 5 6 7 8 Next (pg 1) >> or go to next category: Planets, Stars & Solar System
Sky, Galaxies & Space|
Page 1 2 3 4 5 6 7 8 Next (pg 1) >> or go to next category: Planets, Stars & Solar System
Disks to Planets - The Formation of Stars - How a Star is Born - Part 3 of 3|
From Disks to Planets
Classical T Tauri stars are easily identified by their strong emission lines produced by the disk/star interaction. However, once the disk has dissipated enough so that it no longer interacts with the star, these lines are no longer present or are very weak. These "Weak-lined" T Tauri stars are primarily found because they are bright X-ray sources. T Tauri stars produce X-rays in hot plasma trapped in magnetic fields above the stellar surface. This is similar to the process in which the Sun produces bright flares but 100-1000 times more powerful. X-ray imaging satellites, such as EINSTEIN, ROSAT and ASCA have discovered hundreds of Weak-lined T Tauri stars.
The primary difference between the Classical and Weak-lined T Tauri stars is their disk properties. By the time the star has become a Weak-lined T Tauri star the disk is very weak or no longer present. But where had the disk material gone? The simplest explanation is that it has formed into planets. First, the dust grains form small bodies about 1 kilometer in size, called planetesimals, and then the planetesimals in turn collide together to form planets. Thus, Weak-lined T Tauri stars may harbor very young planetary systems.
The Main Sequence of Events - A Star Grows Up
As the star collapses the temperature and pressure at the core increases. After about 10 million years or so the core gets hot and dense enough for fusion reactions to begin. These reactions convert hydrogen into helium and liberate energy in the process. This energy in turn heats up the star and halts the collapse. This phase of stellar evolution is called the Main Sequence and the star remains relatively stable for a long time (a star like the sun has a Main Sequence phase lasting 10 billion years.) The star has left its childhood behind and settles into a long middle age.
The disk that was formed early in the star's life and began to dissipate in the Weak-lined T Tauri star phases may have formed into planets by now. Perhaps as many as one half of all pre-Main Sequence stars have circumstellar disks and this may mean that half of all Main Sequence stars possess planets.
The Main Sequence star maintains some of the properties of T Tauri stars, although in a weaker form. Main Sequence stars have X-ray emission at a level about 100-1000 times weaker than T Tauri stars. While Main Sequence stars do not have strong outflows, they do possess a stellar wind of charged particles streaming outward from the corona, similar to the Sun's own solar wind. We have been able to learn much about such processes by observing our Sun, which, by astronomical scales is very nearby.
Part 1 Part 2 Part 3
The Yohkoh Satellite captures an x-ray image of the sun, the nearest Main Sequence star to the earth.
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