Does anyone have any information on theories of galaxy formation.?
79909
Some galaxies form in spiral or disk shapes similar to the disks found in star systems.  These are spiral galaxies.  However some, actually the majority, form in sphere like shapes.  These are the called elliptical galaxies.  Do a google image search of "NGC 1316" to see one of these. \n\nGeneral relativity need not be applied to understand the formation mechanism.  Galaxies are believed to form in a similar way that stars form.  You start with a giant spheroidal cloud of material which undergoes gravitational contraction through some kind of induced instability.  The cloud contracts to a smaller size due to gravitational forces and as a result the cloud must spin faster in order to conserve angular momentum (a type of energy conservation).  The last sentence is the real key here. \n\nThe consequence of a contracting cloud spinning faster is to flatten out into a disk shape.  The inward gravitational pull does the "flattening" while the spin-up, so to speak, extends out the disk.  This is analogous to spinning out dough to make a pizza or watching a baseball stretch in the middle as a result of rapidly spinning after a pitch as been fouled off.   \n\nThe motion of the stars and gas in the galaxy does start out random but then is forced into a disk shape as a result of the aforementioned effects.\n\nThere are still a number of mysteries that surround how galaxies form.  Currently we don't know why some galaxies are elliptical while some are spiral?  Can one turn into the other?...among other questions.\n\nI hope that helps.
742823
Astonomers look at: (1) how fast galaxies are rotating, (2) how galaxies are moving relative to each other in clusters, and (3) how galaxies focus light from object beyond them ("gravitational lensing"). They then calculate how much mass there must be in those galaxies to explain those phenomena. Then they measure how much light is coming out of those galaxies and use that to estimate how much mass is in the galaxies. \n\nThe two techniques give very different numbers for the mass in the galaxies. The light measurement method yields a much smaller answer for the masses. Therefore, there is matter in the galaxies that is emitting little or no light.\n\nWhat dark matter is made of is a matter for speculation. Some of it may be neutrinos, which are abundant subatomic particles that were previous thought to have no mass but were recently determined to have a little mass. They are very, very numerous. Some may be "exotic" matter that we yet know nothing about.\n\nIt may be more mundane, however. We know that in our neighbor of the Milky Way, most of the starlight comes from just a handful of very bright stars, while most of the mass is in a large number of small, very dim stars.
275416
The universe is said to be expanding,at least in the sense\nthat all of the galaxies are supposed to be drifting farther\naway from each other.That would seem to contradict your notion of a tremendously big circle as there's no gravitational pull binding them together.\n Also,if space is finite...then what's outside the boundaries?
890850
Yes, our galaxy (and the local group) is generally heading in the direction of the virgo cluster of galaxies. All together, we are moving in the direction of a much larger structure called the 'Great Attractor' that is in the direction of the constallation of Centaurus. I'm guessing that this is what you heard about.\n\nhttp://en.wikipedia.org/wiki/Great_Attractor
1090455
They start out as an enormous gas cloud. Gravity causes the parcicles in the cloud to spin around the point of center mass, and the velocity of the spin subsequently flattens it into a disk. That's how galaxies, and on a much smaller scale, planetary systems form.
73499
The farther we look into the universe with telescopes like Hubble and others, the more galaxies we see. I read a very interesting fact in an astronomy magazine recently that said it is estimated that if you hold your thumb out at arms lenth, close one eye and look at the top of your thumb nail, you are covering up an estimated 240,000 galaxies with your thumb regardless of what direction you look!!!!!! Each galaxy might have an average of 100 to 200 billion stars in them! I have no idea for the estimate of sand grains on every beach in the world-maybe that would be a good question to ask separately in the geography section- but I'm positive that there are quite a bit more stars than sand grains. Good luck!
712328
Wow, getting your science from coast to coast.  That's pathetic.\n\nObserving in the radio portion of the spectrum has revealed massive H2 clouds in other galaxies, which are needed for star formation.  They can only be observed in the 21cm radio line.  We've also realized that many 'radio' galaxies have immense lobes extending out from the galaxy, many times the size of the galaxies, made up of gas expelled from an interior black hole.  X-rays have shown us extrememly hot gas from galaxies and galactic clusters, falling into black holes.
1154361
Hi Decisiveliu\n\nThe most recent observations indicate the following:\n\n* about 70% of the energy density of the universe is dark energy (for physicists this is an omega value of 0.7, where omega is the ratio of the actual density to the critical flatness density)\n* about 30% (omega = 0.3) of the energy density is normal mass-energy\n\n* of this 30%, about 27% is dark matter, and the remaining 3% is baryonic or luminous matter\n\n* about 20% of the total dark matter mass is likely to be massive neutrinos (small weakly interacting particles), about 10% large non-luminous objects (eg black holes, neutron stars, brown drawfs, etc) and the remainder unsure as yet\n\n* of the visible matter the vast majority is hydrogen (as suggested above), followed by helium, and then (relative) traces of other elements.\n\n\nHope this helps!\nThe Chicken
595332
Evolution of Universe\n\nThe three main theories put forward to explain the origin and evolution of the universe are:\n\n   1. The Big Bang Theory\n   2. The Steady State Theory\n   3. The Pulsating Theory\n\n1. The Big Bang Theory: Le Maitre and Gammow proposed this theory. According to this theory, at the beginning of the universe, the whole matter of the universe was once concentrated in an extremely dense and hot (~10 12K) fireball. Then about 20 billion years ago a vast explosion (big bang) occurred. The matter was broken into pieces, which were thrown out with high speed in all directions forming stars and galaxies; which are still moving way from one another. According to Hubble's law, the velocity of recession of a galaxy becomes equal to the velocity of light at a distance equal of 20 billing light years. It means, the light rays from stars and galaxies, which are situated at a distance of 20 billion light years or more, can never reach us. Thus this distance becomes the boundary of observable universe. On account of continuous recession, more and more galaxies will go beyond this boundary and the will be lost. As a result of this, the number of galaxies per unit volume will go on decreasing and ultimately a time may come when we may have empty universe.\n\n2. Steady State Theory: Bondi, Gold and Fred Hoyle developed this theory. According to this theory, the number of galaxies in the observable universe is constant and new galaxies are continuously being created out of empty space, which fill up the gaps caused by those galaxies, which have crossed the boundary of the observable universe. As a result of it, the overall size of mass of the observable universe remains constant. Thus a steady state of the universe is not disturbed at all.\n\n3. Pulsating Theory: According to this theory, the universe is supposed to be expanding and contracting alternately i.e. pulsating. At present, the universe is expanding. According to pulsating theory, it is possible that at a certain time, the expansion of the universe may be stopped by the gravitational pull and the may contract again. After it has been contracted to a certain size, explosion again occurs and the universe will start expanding. The alternate expansion and contraction of the universe give rise to pulsating universe.\n\nWe will now see the theories of planetary motion.
446996
Do you mean SPIRAL galaxies?\n\nCompare the Milky Way (our "spiral" galaxy) with others in the universe. There's a classification for spirals, so it shouldn't be that hard to write a paper on it (without be a physicist)
804251
The Big Bang theory does have a good amount of evidence behind it. So we’ll take a look at the three biggies.\n\na) Cosmological Redshift: We can use spectroscopy to determine the rate at which galaxies are moving away from us. Additionally, since it takes light time to travel, the further away we look, the further back in time we are looking.\n\nWhat we find, is that all galaxies in the universe are moving away from us. The further they are, the faster they’re moving away. So if we play the whole thing in reverse, all the galaxies will come back together at a single point in time. This point in time is what we call the Big Bang.\n\nb) The Cosmic Microwave Background (CMB): Figuring that if you played everything back in time like this that all that energy would be crammed into a smaller space, that means the temperature would go up. And also since galaxies couldn’t have formed yet, we’d expect a gaseous sort of universe early on. As I discussed earlier, hot dense gasses emit photons at a peak wavelength corresponding to their temperature. Unfortunately, since things were so dense, photons couldn’t get very far.\n\nHowever, with the available information, astronomers were able to determine at what density and time, photons would finally be able to get far enough that we could observe them. This is called the “surface of last scattering” and has a very specific temperature. So we should be able to look for photons with energy (wavelength) corresponding to that temperature.\n\nBut due to redshift, they will appear at a different wavelength. This radiation should appear from every direction. This was a prediction made by the Big Bang theory that was later confirmed by Penzias and Wilson who stumbled on it accidentally!\n\nNo other theory of the universe has ever been able to make such a profound prediction to the degree of accuracy the Big Bang did in this instance. Making such amazing predictions is one of the highlights of a good theory. None before or since have ever been able to pull off such a feat.\n\nBut the successes of the CMB prediction don’t stop there. Another important piece of the puzzle lies in that the CMB couldn’t be completely even. If it were, then galaxies couldn’t form since there would be no “seeds” with higher mass and thus a stronger gravitational pull to form around.\n\nThus, the Big Bang theory had to predict that the CMB would not be completely homogeneous. It should have some variations to it, and those variations would have to be of a specific size in order to get the universe we see today.\n\nEarly results for the Big Bang didn’t look too good for this prediction and threatened to sink the whole ship. However, the devices used were not actually sensitive enough to pick up these minute variations. But recently, with the Wilkinson Microwave Anisotropy Probe (WMAP), these perturbations have been discovered precisely as predicted.\n\nScore two strong predictions for the Big Bang. Zero for any others.\n\nc) Distribution of Elements: With the conceptual framework intact thanks to the first point, it was also possible to calculate how much of each element should be formed in the initial event. It should be obvious that, given a bunch of protons, electrons, and neutrons, hydrogen should be the easiest to form. Indeed, stick a proton and an electron in a room together and they’ll automatically hook up due to their magnetic attractions.\n\nAdditionally, with such high energies, it would be possible to fuse some of this hydrogen into helium and even a little bit of heavier elements. Since astronomers had a good handle on the energies, it was possible to calculate how much of each there should be. If that number didn’t match up with observations, the Big Bang theory would be shot.\n\nFortunately, the predictions do match up pretty closely. I stated a value earlier of 80% hydrogen, 20% helium, and neglected the rest since it would be statistically insignificant. In the universe today,
41076
No one knows.  There are theories.\n\nI find the articles in Scientific American to be fascinating reads on the theories and models that physists and cosmologists are developing.  Check out your local library and read, read, read.\n\nIn particular, this article seems to offer information on the latest thinking regarding the state of before the "Big Bang":\n\nThe Myth of the Beginning of Time, May 2004\nhttp://www.sciamdigital.com/browse.cfm?sequencenameCHAR=item2&methodnameCHAR=resource_getitembrowse&interfacenameCHAR=browse.cfm&ISSUEID_CHAR=CB826BAE-2B35-221B-6E2587F29CF2C88A&ARTICLEID_CHAR=CB9AD5CD-2B35-221B-6E241183ECE7749E&sc=I100322\n\nThe other really interesting one is:\n\nMisconceptions about the Big Bang, March 2005\nhttp://www.sciam.com/article.cfm?articleID=0009F0CA-C523-1213-852383414B7F0147&sc=I100322\n\n\nThe universe is too wonderous a thing to limit your thinking about it.
362021
We can only give a rough guess as to how many galaxies there are, and it's billions at least. All but the closest ones visible as galaxies to the naked eye have names. Our local galaxy is the Milky Way, which you can see in a dark place on a clear night as a streak of stars running across the sky. A cluster is a group of galaxies.\n\nSome galaxies we have discovered with Hubble and other new telescopes seem to crashing into each other, and the Milky Way may be on its way to having a galactic interloper in the far future.
1061786
There are actual images of the entire galaxy, but from our position within the disk, it looks a lot like an edge on thin disk with a galactic bulge.  The earliest image of our galaxy that I know of was assembled from IRAS data.  The DIRBE experiment aboard COBE also produces a some nice ones (COBE was a mission to explore the microwave background radiation left over from the big bang.  DIRBE was aboard that spacecraft to characterize the diffuse infrared foreground, namely our galaxy, so its contribution could be removed from the microwave measurements).\n\nDIRBEs shorter wavelength infrared channels trace the stars in the galaxy nicely so you can see the bulge:http://antwrp.gsfc.nasa.gov/apod/ap000130.html\n\nThe longer wavelength channels are more sensitive to dust:http://antwrp.gsfc.nasa.gov/apod/ap000517.html\n\nNote that these are all sky images probably using a Molleweide projection.  The centers look towards the center of the galaxy, but the edges look directly out (away) from the center.  This is a "wraparound" view.
439745
After the finish line of the universe, lies nothing... It's difficult for a human brain to consieve but it's true. \nThough, the universe expands, it's getting bigger as time goes by..\nDid you know that the word galaxy comes from the greek word gala (milk) because in pictures we see that galaxies when seen from far away look like spilt milk!
370961
go to\nhttp://en.wikipedia.org/wiki/Universe
926855
The way to measure it is to measure the redshift of galaxies at different distances. Are they starting to slow down, or not? But like was said above, I'm not going to worry about it. Not that cosmology isn't a fun thing to study, but as far as applications it's just about there with Abstract Art. I would say let's concentrate on applied physics, earth and solar science first, develop some new technologies, maybe colonize Mars, some other solar systems, or a good fraction of the galaxy and then we can worry about the fate of the universe when we have more tools, power and understanding to explore or do something about it. It's noble and admirable, but might be like a caveman pondering the lifespan of the sun - that large bright circle that goes around the flat earth. Occasionally skipping ahead is rewarded - most times it's a shot in the dark.