Galaxy Formation

We really don't know how various galaxies [b][url=http://www.cellphonecasesale.com/samsung-s6-cases-c-9/]Cheap Samsung S6 Cases[/url][/b] formed and took the many shapes that we see today. But we do have some ideas about their origins and evolution.

Edwin Hubble's observations, and subsequent Hubble Law (which we'll explain later), led to the idea [b][url=http://www.cellphonecasesale.com/samsung-s6-cases-c-9/]Designer Samsung S6 Casese[/url][/b] that the universe is expanding. We can estimate the age of the universe based on the rate of expansion. Because some galaxies are billions of light years away from us, we can discern that they formed fairly soon after the big bang (as you look deeper into space, you see further back in time). Most galaxies formed early, but data from NASA's Galaxy Explorer (GALEX) telescope indicate that some new galaxies have formed relatively recently within the past few billion years. In these clouds, gravity caused the gas and dust to collapse and form stars. These stars burned out quickly and became globular clusters, but gravity continued to collapse the clouds. As the clouds collapsed, they formed rotating disks. The rotating disks attracted more gas and dust with gravity and formed galactic disks. Inside the galactic disk, new stars formed. What remained on the outskirts of the original cloud were globular clusters and the halo composed of gas, dust and dark matter.

Two factors from this process [b][url=http://www.cellphonecasesale.com/coach-samsung-s6-cases-c-9_124/]Coach Samsung S6 Cases For Sale[/url][/b] might account for the differences between elliptical and spiral galaxies:

Angular momentum (degree of spin) Protogalactic clouds with more angular momentum could spin faster and from spiral disks. Lowdensity protogalactic clouds cool more slowly, leaving gas and dust for disk formation (like in spiral galaxies).

Galaxies do not act alone. The distances between galaxies do seem large, but the diameters of galaxies are also large. Compared to stars, galaxies are relatively close to one another. They can interact and, more importantly, collide. When galaxies collide, they actually pass through one another the stars inside don't run into one another because of the enormous interstellar [b][url=http://www.cellphonecasesale.com/samsung-s6-cases-c-9/]Samsung S6 Cases For Sale[/url][/b] distances. But collisions do tend to distort a galaxy's shape. Computer models show that collisions between spiral galaxies tend to make elliptical ones (so, spiral galaxies probably haven't been involved in any collisions).