2006-12-27 23:11:35 · 10 answers · asked by Ghavinn V 1 in Science & Mathematics ➔ Astronomy & Space
Yeah, isn't it something.
http://csep10.phys.utk.edu/astr162/lect/galaxies/evolution.html
2006-12-27 23:17:29 · answer #1 · answered by Retired From Y!A 5 · 3⤊ 0⤋
Galaxies were once thought of as "island universes" evolving slowly in complete isolation. Today we think that just the opposite is true: gravitational interactions of galaxies with each other, and even the coalescence of two galaxies into one, or mergers, are commonplace in the Universe! We see striking examples of merging galaxies in the local Universe, such as NGC 2207 and its companion IC 2163 and the Mice. These interacting systems often sport long tidal tails of gas and stars, a result of the mutual gravitational pull of each system. During the merger, the gas in each galaxy disk flow to the galaxy centers, becomes very dense, and forms stars at an alarming rate. This inflowing material also feeds the supermassive black holes at the galaxy centres, which heat up the infalling material to millions of degrees and eject some of it along powerful jets. All of these mechanisms make merging galaxies very bright, such as Arp 220, are among the most luminous objects in the local Universe.
What do mergers leave behind? Both observations of actual systems and simulations of merging galaxies on a computer suggest that merging spirals create elliptical galaxies. The gas in the progenitor spiral galaxies is used up in making stars which subsequently eject heavier elements and dust from the system, and the collision is forceful enough to randomize the orbits of the stars in the incoming disks into a spheroidal shape. Different types of galaxies are therefore intimately linked by galaxy evolution and mergers: spiral galaxies evolve into elliptical galaxies, and irregular galaxies are galaxies in the process of becoming one or the other!
Galaxy coalescence doesn't only happen between two large galaxies: in fact, most large galaxies are constantly swallowing up the smaller, dwarf galaxies that surround them. Our Milky Way is no exception to this rule: it is currently ripping appart our nearest neighbor, the Sagittarius Dwarf!
As you may know, galaxies are mainly of two kinds: spiral galaxies and elliptical galaxies (there are also irregular galaxies).
Spiral galaxies form from the collapse of a protogalactic cloud. Spiral galaxies consist of three components: a rotating disk, a bulge and a halo. When the protogalactic cloud collapses, the stars in the bulge and halo form first. These stars have rather random orbits around the galactic center. The remainder of the cloud forms a disk due to the conservation of angular momentum (the same effect as the spinning up of the dancer when she pulls her arms inside). The stars in the disk form later and thus the disk population of stars are younger than those in the bulge and the halo. Further, the stars in the disk rotate around the center of the galaxy in a collective, well defined way unlike the stars in the bulge and halo.
Elliptical galaxies are thought to be formed as a result of a merger of two disk galaxies. When two spiral galaxies merge, then the orbits of all the stars are randomized. As a result, all the stars in an elliptical galaxy have random orbits and there is not much collective motion of stars.
2006-12-28 10:18:02 · answer #2 · answered by Sporadic 3 · 0⤊ 0⤋
Huh? I don't really get what your question is.
But know this: Many of the galaxies in our Universe have evolved over billions of years, and there are more GALAXIES in the Universe than there are grains of sand on every beach in the entire world. Not an assumption, that is a fact.
And an average galaxy contains between 100 million to a TRILLION stars, each one like our own sun with the possibility of orbiting planets and therefore extraterrestrial life.
Er, WOW.
2006-12-28 07:15:26 · answer #3 · answered by Buck Flair 4 · 1⤊ 1⤋
Like everyone else here, I am not to sure what your question is. Please be clear so we can help you.
If you are referring to the creation and expansion of the universe as is believed to have happened during the Big Bang, I can direct you to the excellent book by Simon Singh called (wait for it...) The Big Bang. Its a very readable general science book and explains just about everything in a way that won't make you run for cover from men in white coats with extraordinary beards.
2006-12-28 07:27:19 · answer #4 · answered by Finlay S 3 · 0⤊ 0⤋
The expansion of the universe?
2006-12-28 07:14:52 · answer #5 · answered by Anonymous · 0⤊ 0⤋
no one knows they just have theorys, a popular one is the earth formed by collecting dust ,but how did the hot core form ? you see no one knows how what or when ,there just theories
2006-12-28 07:20:08 · answer #6 · answered by Anonymous · 0⤊ 1⤋
still evolving
2006-12-28 18:25:38 · answer #7 · answered by NIGEL R 7 · 0⤊ 0⤋
they came into being - they were unwrapped - they were eaten
2006-12-28 07:13:44 · answer #8 · answered by Anonymous · 0⤊ 1⤋
exactly my friend exactly
2006-12-28 07:13:33 · answer #9 · answered by tbone 2 · 1⤊ 1⤋
care to elaborate at all???!!!!?
2006-12-28 07:13:23 · answer #10 · answered by Anonymous · 1⤊ 0⤋