Hard Light Productions Forums
Off-Topic Discussion => General Discussion => Topic started by: mr.WHO on April 30, 2005, 01:41:03 am
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Do you know where I can find a map of our galaxy (even better if its 3D and have a recend discovered solar systems).
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Umm, maybe whole galaxy is too much but nearest sector(200-500 light years from Earth) should be mapped??
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www.solstation.com
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Ever find it amazing that our solar system's position in the galaxy is in the best place to view the universe? We arent in the arms or the center where its to "cloudy" with cosmic crap to observe but we are between one of the arms which alows us to view the rest of the universe.
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http://www.shatters.net/celestia/
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Iv'e always wondered, whats at the center of a galaxy?
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Some say an übergiant black hole, that would explain the rotation and the cluster at the center. But woulent the galaxy collapse in on itself? Or is the supposed 'dark matter' stuff holding it in place?
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A black hole at the center of the galaxy would collapse the galaxy in the same way the sun at the center of the solar system would collapse it.
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Oh, I see... Thanks for the clarification. :yes:
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I always find it funny when someone uses a real galaxy picture as a map of the Milky Way. Like you're ever actually going to get that picture :rolleyes:
We're actually near the edge of one of our galaxy's arms, not out in the void between them. But yes, we are far enough removed from the relative chaos of the galactic core to make observation (and life itself) far easier.
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Clearing up some misconceptions:
The "voids" between galactic arms do have about as many stars as the arms themselves. It's the difference in dust amounts that scatter light which causes how it looks.
The galactic core, according to recent observations, has several high energy sources. We're looking at dozens of massive blackholes in the galactic core. Not so different from the core in Homeworld 2.
We're in a "good spot to observe the universe" mainly because at the age of the milky way stars with higher metallicity are towards the edge, making this region the habitable zone. Several billions of years ago, this habitable zone was closer to the galactic core. Of course, gamma ray bursts would be more common in that part, so there is a good chance that life never got as far there as it will out here.
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Originally posted by StratComm
I always find it funny when someone uses a real galaxy picture as a map of the Milky Way. Like you're ever actually going to get that picture :rolleyes:
Well, I would've gotten a real picture of our galaxy, except I couldn't find the one that Hubble took. :p
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http://www.shatters.net/celestia/
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It's probably some sort of balance between centripetal force, the gravity exterted by the black holes, and dark energy that holds us at a distance from the core.
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Originally posted by Ghostavo
A black hole at the center of the galaxy would collapse the galaxy in the same way the sun at the center of the solar system would collapse it.
Hehe :p For those of you who may not know, black holes don't "suck" surrounding matter into them. If you get beyond a few times their Schwartzchild radius (the "event horizon"), the only thing influencing orbits around them is the simple law of gravity. If the Sun were replaced by a black hole of the exact same mass, absolutely nothing would change about the orbits of the planets, other than the fact that we'd all freeze to death, of course. :p
Multiple black holes near the center of the galaxy? Do you have a reliable source for this? Last I heard, through detailed radio observations of the orbits stars at the very center of the galaxy, the object they were all orbiting was something on the order of two million solar masses, which could only be a supermassive black hole. Having multiple supermassive black holes would obviously make these orbits much more complex; from the images I've seen, they're pretty much regular. As far as I know, the only such supermassive black hole that's been detected at the center is Sagittarius A*; just recently, in fact, scientists observed X-ray bursts caused by matter falling into the black hole, backing up this theory.
As far as the solar system being in a perfect spot to view the rest of the universe, it's really not so perfect as you might think. Sure, we're in the arms of the galaxy instead of the core, which helps aid in visibility, but so are billions of other star systems out there; this doesn't necessarily make us special. Actually, if we're talking about viewing in the plane of the galaxy, we can't see visually more than a few hundred light years before the interstellar medium obscures our view; that's why we've had to use infrared and radio light to observe most of our own galaxy. I'm not saying that we have a bad view of the rest of the universe (a good telescope and a guide to the many visible galaxies in the night sky are testament to that), but it's not necessarily anything special.
As far as the orbit of stars in the galaxy goes, this is a subject that I just touched on in an astronomy class, so I can shed a little light on the subject. By using the Doppler effect to look at spectral shifts of galaxies edge-on to our own, we can determine the rotational speed at different distance out from the galaxy's center. The results obtained from these observations were far different than anyone expected. Here's an easy metaphor: in the case of our solar system, the orbital velocity of objects such as planets decreases in an inverse square relationship. This is to be expected due to Newton's law of universal gravitation, which states that the gravitational force drops off by one over the distance squared. Since over 99% of our solar system's mass is in the Sun at the center of our solar system, mass is taken out of the equation, and so the orbital velocity follows this simple law.
Astronomers were expecting that this same pattern would be present in galaxies; since they could estimate the number of stars in each part of the galaxy based on their apparent brightness, they knew that the majority of a galaxy's visible mass was concentrated in the core. Following from this, the orbital velocity of stars at the edge of the disk should be substantially less than that of stars near the core, since the distance increased with no substantial change in mass. Lo and behold, they were dead wrong. The orbital curves of every galaxy we've measured show a constant velocity as one moves further away from the core; in other words, the stars in the farthest reaches of the disk orbit at the same rate as those near the core. By Newton's gravitational law, this can only be true if the mass inside the orbit of these stars is increasing rapidly enough to offset the incresing distance. Based on the number of stars that we've observed, we know this can't be the case. Instead, according to current theories, there has to be some other form of matter, which accounts for about 90% of the galaxy's mass, that is causing this discrepancy. We call this dark matter, since we've never directly observed its presence. The objects orbiting in the Milky Way Galaxy aren't simply influenced by the two-million-mass black hole at its center, or the masses of the millions of star systems and gas clouds inside their orbits; that doesn't come close to accounting for their speed. Instead, this dark matter is responsible for keeping the stars in their regular orbits. Dark matter is pretty much on the cutting edge of physics; it's a subject that we know very little about. From what I've heard, there are papers on it out there that make general relativity look like kindergarten. :p