I'm sure this is a totally newbie question, so any website references would be appreciated. <br /><br />I was looking at images of galaxies online and trying to get a sense of what was going on. It seems like there is a bar at the center and two main arms spiraling outward. To me, just from viewing the image, it seemed like it was blasting out in two opposite directions, with the gravity of the center curving the arms as they shot outward, like those spinny little chinese fireworks. But then someone told me that the arms were actually being pulled inward by a massive black hole at the center. So which is it? Are the arms getting sucked in by the center or spewed out by it?
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I would say that they are neither getting blown out or sucked in. Astronomers still aren't completely sure what causes a spiral galaxy to be barred. <br /><br />I don't always use wikipedia, but here is some info on barred spiral galaxies. It is theorized that this bar found in galaxies might act as a stellar nursery.<br /><br />http://en.wikipedia.org/wiki/Barred_Galaxy<br /><br />Another thing that has somewhat baffled astronomers is how the spiral arms of galaxies rotate as one entity. In other words, their spiral shape does not mean that the motion of stars within the galaxy would resemble water going down a drain. One theory suggests that this is solid evidence for 'dark matter'. <br /><br />The arms are not being sucked in because even if a supermassive blackhole exists at the center of the galaxy, it doesn't have a large enough radius to consume the entire galaxy. The supermassive blackhole, I believe, is what holds the galaxy together. Many astronomers believe that these supermassive blackholes are what create galaxies.<br /><br />This idea of how galaxies are formed has theories of its own. One theory states that these supermassive blackholes might be the stellar corpses of some of the earliest stars that ever existed in the Universe. These were VERY massive stars that did not live very long lives, and they died off in incredibly strong supernovae. <br /><br /> <br /><br /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
Oh and I almost forgot. Welcome to SDC!! <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
Weeman:<br /><br />Thanks for the insight and reference. Unfortunately, I'm unable to access wikipedia from my location.<br /><br />Your static notion of simple rotation is probably the most backed by science. After all, ancient, less refined, galaxies have been seen with Hubble. But just from an intuitive sense, it sure looks like an explosion to me. <br /><br />So let me phrase my question another way: If we are viewing a galaxy face on from the side where the arms are curving to the right, is it turning clockwise (exploding outward) or counterclockwise (getting sucked inward)? Or, as I just learned, with a galactic year being somewhere on par with the age of the universe itself, do we even have any way of knowing?<br /><br />
I think its completely possible that our universe was created by a Black Hole. When the “Big Bang” occurred I think that an extremely enormous Black Hole had collected so much matter (planets, stars, comets, light, etc.) that it exploded all of this matter through the other end, typically known as the White Hole. The Black Hole is in a separate dimension and this is where matter is sucked in. The Black Hole will store this matter until it has so much of it that it cannot hold anymore causing a massive burst of matter through its exit passage, or White Hole. The White Hole is the entry point for new matter into a new universe/dimension. For example, I think that our galaxy and any other galaxies were formed by periodic explosions from a number of White Holes that may be located in this realm/dimension/universe/plane of existence (whatever you want to call it). We then float around in space. <br />Our galaxy in particular has a Black Hole located at it’s galactic center. Some people, including myself, believe that we will approach this Black Hole and our galactic center around the year 2012. If our solar system happens to breach the Black Hole’s Event Horizon then we will all be sucked into it. We may travel through it immediately and come out of the White Hole in a new dimension or universe. It is also possible that we will be stuck inside of the Black Hole until it decides to push us through its exit hole into a new world. Think about our human bodies as a small microcosm of the way the universe works. We eat food and “matter” into our “Black Hole”, which is our mouth. It travels through the intestines or “worm hole” until it reaches its exit point or “White Hole”, where the matter is released back into the world. These are just my thoughts but let me know what you think. Am I crazy or do you think this makes any sense? <br />
To be honest, I'm not too sure how to answer your question, I don't really have any idea. If the bar in galaxies means that new stars are being formed, then I suppose you could say that it is exploding outward.<br /><br />It certainly requires more patience and time than we have as humans to observe a galaxy's motion. Take the Milky Way for instance. The Milky Way is about 100,000 lightyears across, our solar system sits about 2/3 of the way out from the galactic center. From where our solar system sits, a galactic year is about 230 million Earth years. <br /><br />So, Mankind has hardly been around for a fraction of that to observe a large galaxy's motion. I heard a while back about the technique of how astronomers can tell of a galaxy's rotation. I can research it, unless someone else on this board knows the answer.<br /><br />The issues that astronomers have with galaxies is that they seem to break a rule of physics, at least when first observed. The stars near the center of the galaxy should rotate faster than the stars near the edge, but this is not the case. For example, when a figure skater pulls her arms close to her body she will spin faster than when she stretches her arms out straight. Astronomers have found that the galaxy moves as a whole, as if all the stars are fixated on a flat surface that is spinning. One answer to this problem is dark matter. If there is missing mass, or at least invisible mass within the galaxy, then it might solve this problem that we are having trouble understanding.<br /><br />I'm curious, where did you learn that a galactic year is around the same age as the Universe? What's being defined as a galactic year?<br /><br />Like I stated above, 230 million years is a galactic year from where we stand. However, this is not the same for different regions of the galaxy. Galactic years will also range from galaxy to galaxy depending on size. <br /><br /> <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
I may have gotten my millions and billions confused on the galactic year thing
<br /><br />I thought the direction of a galaxy's spin would be common knowledge in cosmology. The only reason I even raised this issue was that I couldn't stop staring at the image I had downloaded and was hoping to get some sort of definitive answer. But it looks as though I've stumbled upon the unknown. <br /><br />Very interesting that it seems to move as whole, kind of like a vinyl record on a turntable, rather the opposite of how a solar system works. Yet... how can they know that if they can't even tell which direction it's spinning in?<br /><br />I came upon one webpage that postulated two holes, black and white, at the center acting as some kind of reactor that spits matter out one side and antimatter out the other. Another site also noted that stars are abundant between the arms in what appears to be empty space, and that the visible arms are just where the brighter larger stars tend to coalesce.
<br /><br />I thought the direction of a galaxy's spin would be common knowledge in cosmology. The only reason I even raised this issue was that I couldn't stop staring at the image I had downloaded and was hoping to get some sort of definitive answer. But it looks as though I've stumbled upon the unknown. <br /><br />Very interesting that it seems to move as whole, kind of like a vinyl record on a turntable, rather the opposite of how a solar system works. Yet... how can they know that if they can't even tell which direction it's spinning in?<br /><br />I came upon one webpage that postulated two holes, black and white, at the center acting as some kind of reactor that spits matter out one side and antimatter out the other. Another site also noted that stars are abundant between the arms in what appears to be empty space, and that the visible arms are just where the brighter larger stars tend to coalesce.Clockwise or counterclockwise likely do not suggest either exploding outward nor getting sucked in: but do possibly signify top view or bottom view.<br />I think we have determined that our galaxy is rotating with respect to the very distant stars, even though we have rotated only about one second of arc in recent centuries. I doubt that we have measured the rotation rate (if any) of galaxies farther away than our local group of galaxies. Rotation is infered, rather than measured. Neil
Cannot open wikipedia...<br /><br />I hope you can open this article:<br />http://unisci.com/stories/20021/0207023.htm <br /><br />Have a good time in SDC.
Thanks for the link:<br /><br />(http://unisci.com/stories/20021/0207023.htm): "Most spiral galaxies have arms of gas and stars that trail behind as they turn." <br /><br />So this is pretty much the consensus? <br /><br />I fully realize that finer minds than mine are figuring this stuff out, and I'm only basing my idea on a kind of "horse sense" which the truth is more than welcome to defy. But how can we be sure a galaxy actually "rotates" as a whole? Perhaps a different process is going on that creates that appearance. I mean, it's obviously nothing like the mechanics of a solar system. Planetary orbits are elliptical, but most galaxy are swirling vortexes. As stated by Weeman, the outer periphery is believed to turn in sync with the inner reaches. That doesn't sound like orbiting to me. If everything were just orbiting around the center, we would see rings instead of appendages. But if the core was spewing material out two sides, and the gravity of the core wrapped the arms back around itself as they continued on their outward vector, we would see spiral arms. This process would also have a sling shot effect on the matter, accellerating it on its outward trajectory and possibly explaining the appearance of 'inner/outer uniform rotatation'?<br /><br />Again, I know I'm talking entirely out my butt with regards to figures, facts, and research -but it does make a certain sense. Cuz when I look at those massive things we call galaxies, I just don't see a spinning disc -I see a firework.<br /><br /><br />(http://unisci.com/stories/20021/0207023.htm) "But this galaxy has two "leading" outer arms that point toward the direction of the galaxy's clockwise rotation."<br /><br />How can they be sure this is the exeption rather than the rule? Maybe both kinds are out there. I can imagine a process where the galaxy ejects matter out in spiral arms, and once the core is depleted, the process reverses and the matteria heads back into that common center of gravity along the s
Wow! I just ran across this site on "Plasma Cosmology". It has a lot of elements that jive with my thinking. <br /><br />http://www.matter-antimatter.com/plasma_cosmology.htm<br /><br />What do the experts around here think? Is it plausable, good science?
<font color="yellow">But how can we be sure a galaxy actually "rotates" as a whole?</font><br /><br />They can measure the rotation of a galaxy by the difference in doppler shift between one side and the other. If you look at a galaxy that is tilted so it looks about flat to us then the side that is coming "toward" us in rotation will be bluer than the side that is moving "away" from us. This link, to the middle of a page, shows how it is done:<br /><br />http://spiff.rit.edu/classes/phys301/lectures/doppler/doppler.html#rotgal<br /><br />This link has more information about the "backwards" one. That one was probably harder because it isn't edge-on from our point of view.<br /><br />http://bama.ua.edu/~rbuta/ngc4622/aas199_52.08.html <div class="Discussion_UserSignature"> </div>
<blockquote><font class="small">In reply to:</font><hr /><p>But how can we be sure a galaxy actually "rotates"?<p><hr /></p></p></blockquote><br /><br />galaxy rotation (rate and the direction) is measured best when we see it directly side on - edgewise, that is as narrow disk with central bulge sticking out to sides in the middle, then we examine spectral measurements and find one end of the disk is blueshifted relative to the other end which is redshifted and then we know that the redsifted end is moving away from us while the blueshifted end is moving towards us (that is BTW how the Dark Matter phenomenon was discovered)<br /><br />when a galaxy is oriented exactly edgewise to us, it is easiest to measure the rotation but we can't see it arms and so can't tell which way they point, on the other hand if we see the galaxy directly face on as a circle with the central bulge as light area in the middle, then we can't really measure the rate or the direction at which it spins because the method of the blue-red shift measuring fails us for obvious reasons<br /><br />therefore the best orientation for determining the spin rate and direction of a galaxy rotation is some compromis when its not either fully face on or fully edge on towards us<br /><br />from such measurements it was determined that all spiral galaxies spin so as to have their arms trailing behind (as per commonsense view)<br /><br />I said 'all' because it that wasn't so, nobody would be surprised at this one finding, so if you want to know as somebody who is new to and wants to learn astronomy, you should learn that all spiral galaxies spin so as to have their arms trailing, period. reason is that this case is the first time occurence and it is doubtfull the finding was correctly interpreted as witness there is also talk about some anomalous happening, a collision or something, might be mere superposition of two galaxies, who knows - point is how did they figure the direction this galaxy rotates when it is face on towards us, <div class="Discussion_UserSignature"> </div>
a few posts up someone had a comment on the galaxy moving as a whole,<br />I just wonder how else in the world can it move?<br /><br />I am thinking of possible special scenarios, like a merged galxy, which I think ours is, but <br />otherwise on a average galxy wouldn't it either rotate or not?<br /><br /><br />and then a post had a question about do we spin to the east or to the west? I think a more<br />accurate question would be does the galaxy spin towards the tip of the arms? or does it spin<br />leaving the arm tips behind?<br /><br /><br /> <div class="Discussion_UserSignature"> </div>
"a few posts up someone had a comment on the galaxy moving as a whole, I just wonder how else in the world can it move? "<br /><br />Actually, I addressed that. The question was rhetorical to my argument, part of a longer line of logic that idicates it is swirling outward or inward along the arms (just as it appears to be!) rather that simply just "rotating".
"I think a more accurate question would be does the galaxy spin towards the tip of the arms? or does it spin<br />leaving the arm tips behind?"<br /><br />Yes, well phrased. That was the initial question I came here with. The answer seems to be (B) the arm tips trailing behind. But the link posted by SEARCH shows there is at least one exception.
<font color="yellow"> a few posts up someone had a comment on the galaxy moving as a whole, <br />I just wonder how else in the world can it move? </font><br /><br />I galaxy should rotate no matter what. All stars in the galaxy will move whether they are just a few lightyears from the center or they are at the very edge.<br /><br />The closer you get to the galactic center, the faster the rotation should spin. However, it doesn't seem to be this way. This is where it was indicated in the previous post that the galaxy moves as a whole. The way I see it, the galaxy would NOT be moving as a whole if the stars that are 3,000 lighyears from galactic center were moving faster than stars that are 40,000 lightyears from galactic center.<br /><br />Astronomers see the stars throughout the entire galaxy moving together, this is what astronomers use as evidence to support the theory of dark matter. <br /><br />Of course, I wouldn't include the movement of stars that are very close to galactic center for my argument. Stars that are within a few lightyears (or closer) to the supermassive blackhole I believe are moving at very high velocities. <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>
Check out this thread on Spirals <div class="Discussion_UserSignature"> <p><font size="2" color="#ff0000"><em><strong>I'm a recovering optimist - things could be better.</strong></em></font> </p> </div>
instead of a galaxy, think of our solar system<br /><br />Earth makes some 250 orbits in time that Pluto makes just one orbit (or so approximately, don't get hung up on precise figures)<br /><br />now if somehow we found Pluto doing its one orbit in time that the Earth made just 200 orbits, we would suspect some dark matter in the solar system, same as we suspect it in galaxies for similar reason (outlying parts of galaxies orbit faster than they should)<br /><br />now if Pluto were orbiting that much faster, it still wouldn't make the solar system behave like vinyl record and the same with galaxies<br /><br />only with galaxies astronomers never 'see them move', its all about measuring those spectra shifts I talked about<br /><br />bottom line is galaxies are not moving 'together' but they move together more than they should by normal reckoning, ie. as you move to center of galaxy, stars do move faster (orbit galaxy nucleus faster) than those farther out, its just that the orbit gradient is not quite as it should be but gradient there is, in time galaxies will change if you could live for millions years to watch it and it will be because of that orbital gradient<br /><br />and of course, all those galaxies analyzed up to now rotate so as to have their arms trailing, all except the ONE that is and I don't believe it is possible for a galaxy to turn that way, it is some sort of misinterpretation IMO, lets see if there are many like that, then I might reconsider<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>
But if our Sun were spitting out a steady of stream of Plutos from either side of itself, perhaps our solar system would look like a vortex (galaxy) with two spiral arms of Plutos swirling outward from the Sun. <br /><br />Again, my point is: why are the arms assumed to be static? Clearly the most powerful and largest thing we know of in the Universe is a galactic core. If matter was just orbiting it in rings (do ringed galaxies even have a core?) that would be one thing. By why arms? Why the bar? What precludes this possibilty of the matter moving along the arms? Whirlpools and twisters suck matter in, they don't keep spinning the same molecules around over and over again. In the case of a galaxy, it really looks like matter is getting ejected out the sides of that whatever-it-is at the center and moving outward. Why else would there be arms? I know this sounds a little silly, but I wasn't born with arms "orbitting" around me. I GREW them from my torso when I was an itsy bitsy fetus.
<font color="yellow">why are the arms assumed to be static? </font><br /><br />I don't know that they are assumed static, so far nobody knows nothing certain I think, like how the arms come about and what will happen to them in time, evolution of galaxies is still in hypothesis or speculation stage I believe but I also think that generally the idea is that galaxies are not static - stable un-evolving structures<br /><br />I have an idea that the spiral arms are the way how galaxies are begining to come appart although they do not have to break up, in a way this feature of galaxies (of developing the arms) might be the manner how they manage to stay as one body (but more loosely bound) in continually expanding space (universe) instead of having to break appart (it has implications for gravitation)<br /><br />so that instead of the arms being ejected (by some active process) they are the result of the changing conditions of space which were different in times when the galaxies were collapsing/forming and could support larger compact matter agregations<br /><br />those are all interesting question you raise but I am affraid we can't start getting answers to them as long as we don't understand the 'Dark' secrets of the universe, the DM & DE<br />it is quite plain that those would play major role in galaxy development and probably are the key to understand galaxies, especially the DM phenomenon<br /><br />while the arms are trailing, it doesn't have to imply that the galaxy is 'winding up' into more tight formation as time goes on, rather it might mean that those arms are the process of unwinding of galaxies - Dark Matter means that outlying parts of galaxies are orbiting somewhat faster than they should which might lead to the gradual unwinding - /> peeling off layers of galaxy due to a slightly increased orbital speed above normal of outlying parts relative to the core of galaxy (which speed may have gradually gained in magnitude over past eons) and perhaps this p <div class="Discussion_UserSignature"> </div>
I will have to read all you guys said some other time. It looks interesting. <br />Check out these simulation: http://www.preston.u-net.com/AGMatter/Sim3Clusters.htm <br /><br />I like the solar system analogy. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <div>________________________________________ <br /></div><div><ul><li><font color="#008000"><em>your move...</em></font></li></ul></div> </div>
<font color="yellow"> But how can we be sure a galaxy actually "rotates" as a whole?</font><br />The answer to your question is in Vera Rubin<br />By examining the spectra, or light signatures of galaxies, she made another discovery in the early 1970's that altered dramatically our understanding of the universe. Newtonian laws of gravity predict that stars on the outside edge of a spiral galaxy would orbit slower than stars in the center of that galaxy; like planets orbiting around the sun. Vera's research shows that they do not. Stars orbiting the outside of a spiral galaxy travel just as fast as those orbiting closer to the center. As a result of her unexpected finding, scientists now believe that there is some huge, invisible mass exerting the gravitational force necessary for those outer stars to stay in orbit. Vera Rubin's research suggests that at least 90% of the universe is made of "dark matter," a substance that scientists today struggle to identify and describe. Rubin's work has shown that we still know only a fraction about what the universe is made of.
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