Creation of the Universe
From Mbscientific_wiki
Creation of the Universe- The Big Bang/Inflationary Model
The prevailing theory says that all energy-matter in our space-time bubble was created in a Big Bang event. The event created an inflating space-time bubble full of super-hot elementary particles. As the bubble expanded, the particle soup cooled down to the point that the present protons, neutrons and electrons had a chance to bind and create elemental atoms of hydrogen (and some helium). Massive hydrogen clouds, under gravitational attraction, coalesced to form galaxies (Source: http://www.gsfc.nasa.gov/topstory/2003/0206mapresults.html)(| See it in a movie).
Let's start with some observations and see how they lead to the big bang and inflationary models for the creation of the universe. The main observation, now termed Hubble's law (named after the person who made the observation), is that galaxies are moving away from each other, i.e. the universe is expanding(| See Hubble Deep Field Diagram)(| see expansion movie). He did that by looking at the radiation signature of known elements like hydrogen in distant galaxies. Say, hydrogen when thermally excited radiates at a given frequency. If the object is moving towards you, the wavelengths squeeze together making it appear a bit bluer, if it moves away from you the opposite happens and it appears redder. We call this the red shift. Almost every thing is red shifted regardless of what direction we look, meaning everything is moving away from everything. The exception is nearby galaxies (in galaxy groups) that are relatively moving towards one another, but all distant galaxies appear to be moving apart. So imagine in your mind, a movie of these objects moving away from each other. Now reverse the movie and look at it going backwards in time, everything will be moving towards each other. The logical conclusion would be that at some particular point and time every thing would come together. The big bang theory then proposes that it all started with a big bang that started the movie. Another observation that lends credence to the big bang idea is that of the cosmic background radiation. No matter in what direction we look, we find a radiation signature that corresponds to a temperature of ~3 degrees Kelvin. One explanation is that it is the after glow of the big bang event. So you had this initial explosion. Then everything cooled down (other than the regions where stars formed and heated back up again). And what we see today is the uniformly cooled aftermath of the big bang event that after some 14 billion years is now at a uniform ~3 K, regardless of where you look (| See COBE background radiation animation) (| Back ground Radiation and Galaxy Formation movie).
Big Bang Theory explains a lot of the observations but not all. You see, all matter at any given temperature vibrates. That motion results in it radiating at a given frequency. We can detect any frequency, so theoretically we should have a radiation signature of anything (any matter that is out there). There in is the problem, as we are about to see.
Dark Energy and Dark Matter
Suppose Big Bang is a given, it did explode 14 billion years ago and everything started to expand out as the result of the momentum of the explosion. So you have all these objects receding from one another. The only force exerting on them will be their mutual gravitational attraction pulling them towards one another, thereby counteracting the initial outward momentum. So over time you expect that the rate of expansion will slow down. People started to look at certain super-novas at large distances away, expecting to see slowed expansion the further out they looked. There would be more matter between us and the observed object, therefore more gravitational attraction, therefore more of a slow down. And taking that logic to conclusion, the objects farthest away, say 14 billion light years or so, would have all of the gravitational force of the universe acting on it and pulling it back and very little matter in front of it to attract it forward. At least that's what people thought. Well, the observations showed the exact opposite result. Not only distant objects aren't slowing down, the further out we look the more they are speeding away(| Chandra Animation. And that is true for all directions. So there is something that is continually pushing these objects away from one another, something with negative gravity. And, this stuff, called dark energy, is evenly distributed because its effects are uniform regardless of what direction we look at. The problem is that we can't detect it with anything so far. The only effect we observe is the repulsive gravitation that I just described. So it is not matter, because that has positive gravity, pulling other matter towards it. It's not pure energy, ala photons, because that has no mass and no gravitation. Somebody had to call it something, so they call it dark energy.
And here is another observation. When we look at some galaxies, say our own milky way, we find most of the stellar matter bunched up around the core. By contrast, you have relatively little star formation in the outer bounds. Again if gravity was the only force in effect, then you'd have very fast rotation in the middle and relatively little rotation out on the perimeter. Think of your kitchen sink. When you have a lot of soap water (for those of you that have actually washed dishes), you see fast rotation near the drain and relatively little rotation on the outside. You'd expect that. You only have one force, gravity, effective at the drain and exerting most force on the nearby material. We don't see that in the case of the spiral galaxy of our example. The stars on the perimeter are moving at the same relative rate as the stuff in the middle. The outer stars don't drift off. They keep formation. So some other force is hemming them in. But nothing can be detected that could exert such a positive gravitational force. The same thing holds when we look at galactic groups and clusters, e.g. the Virgo super-cluster. We see all of these far-flung galaxies in the cluster and they keep formation. But there aren't enough observed matter in the cluster to pull them together. And if one calculates the amount of matter that it takes to exert the gravitational force to pull the galaxies together, one comes up with far more than the observed matter that is accounted for. So there is something out there, in vast quantities, that doesn't radiate and has positive, matter-like, gravitation. So people started calling it dark matter.
There is a whole cosmic industry trying to theorize the nature of dark energy-dark matter. And it is noteworthy that per our current theories and observations, it is thought that that dark stuff comprises some 90 percent of the energy budget of the universe. Some call this the golden age of cosmology because there is so much to be discovered. I personally call it the nickel age of cosmology because there is little money in it.
Galaxy Formation - Creation of our Familiar Cosmos
Regardless of the theories of the creation of the universe and the problems therein, there are these elementary particles that start off the morphological flows. Among them, the stable electron-proton-neutrons bind to create the simplest atom, hydrogen, in vast quantities of gases. As gas clouds become denser due to gravitational attraction they heat up and eventually coalesce to form proto-galaxies. Proto-galaxies are dense gas (mainly hydrogen) clusters that act as stellar nurseries. As proto-galaxies settle, we end up with the galaxies that we observe today. We see spiral galaxies, lenticular galaxies (spiral galaxies with missing spirals), elliptical galaxies that look like cosmic footballs, and irregular galaxies (pictured below in that order, source: http://www.seds.org/messier/galaxy.html)
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We often find galaxies in groups (few to tens), clusters (hundreds) and super clusters (thousands) (| see it in a movie). Irregular galaxies are thought to be galaxies that, under the influence of nearby galaxies in their group, never had a chance to form. Our own milky-way galaxy is orbited by 2 irregular galaxies called the large and the small Magellanic Clouds. Sometimes one galaxy in a group absorbs another galaxy in the group. Within the galaxies you typically find:
- Globular star clusters, large, compact aggregates of hundreds of thousands of stars, often the oldest stars in the galaxy.
- Stellar nebula remnants - As the stars develop, many of them leave nebulous remnants (planetary nebulae or supernova remnants) which then populate the galaxies.
- Outer-bound regions- the interstellar gas and dust tends to accumulate in clouds near an equatorial disk and flatten out at the outer regions, most conspicuous in spiral and lenticular galaxies.
- Interstellar clouds - huge diffuse nebulae where clusters of stars are formed.
- Nucleus- A rather dense galactic nucleus, which is somewhat similar to a super-large globular cluster. In many cases, galactic nuclei contain super-massive dark objects, which are often considered as Black Hole candidates.
Courses
Courses from Massachusetts Institute of Technology (MIT) OpenCourseWare:
http://ocw.mit.edu/OcwWeb/Physics/8-286Spring-2004/CourseHome/index.htm - MIT - 8.286 The Early Universe
http://ocw.mit.edu/OcwWeb/Physics/8-282JSpring-2006/StudyMaterials/index.htm - MIT - 8.282J / 12.402J Introduction to Astronomy
Links
(note: right click on link to open in new window or tab)
http://chandra.harvard.edu/resources/animations/index.html - Chandra (x-ray observatory) Harvard Animation series
http://en.wikipedia.org/wiki/Galaxy_groups_and_clusters - Galaxy groups and clusters at wikipedia
http://en.wikipedia.org/wiki/Galaxy - Galaxy anatomy at wikipedia
http://seds.org/messier/gal_clus.html - Galaxy groups and clusters, messier catalog
http://www.nasa.gov/vision/universe/starsgalaxies/hubble_UDF.html - Hubble deep field goodies
http://www.nasa.gov/centers/goddard/news/topstory/2003/0206mapresults.html - Background Radiation Goodies from the folks at NASA Goddard
http://www.youtube.com/watch?v=faRb8VW13pg - lots of big bangie animation YouTube
http://ssscott.tripod.com/BigBang.html - Article on big Bang Theory
http://nedwww.ipac.caltech.edu/level5/Guth/Guth_contents.html - Article on Inflationary model by Alan Guth
http://www.hcc.hawaii.edu:8000/cgi-bin/HyperNews/get/forums/astro-f02-15/7/1.html - An article on a recently discovered proto-galaxy
http://www.seds.org/messier/ - A good Galaxy catalog - the Messier Catalog
http://www.astr.ua.edu/keel/galaxies/ - Galaxies and the Universe- a WWW course
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