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Question on Gravity/black holes/galaxies.
Okay I understand that current thinking leans towards hidden matter in the
spiral arms of our galaxy. And that a black hole is at the center of the galaxy. Couldn't the problem of the spiral arms not "flying off" be due to the possibility that they are in the Event Horizon of the galactic center? Would we still need hidden matter even then? It just seems kind of "extra" and not fitting quite right with Occam's Razor to me. -- --XeNO "Order of the Eigth Digit" www.digitalmessiahmusic.net (no the band is not religously themed.) AA# 1901 "In Hoc Signo Vinces" ----------- . ----------- \ | / \ / / \ / | \ ----------- . ----------- |
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"XeNO" wrote in message news:mhhec.951$fS6.831@okepread01...
Okay I understand that current thinking leans towards hidden matter in the spiral arms of our galaxy. And that a black hole is at the center of the galaxy. Couldn't the problem of the spiral arms not "flying off" be due to the possibility that they are in the Event Horizon of the galactic center? Would we still need hidden matter even then? It just seems kind of "extra" and not fitting quite right with Occam's Razor to me. There are a few problems with this hypotheses. First, a black hole with a Schwarzschild radius (event horizon) large enough to encompass the spiral arms of the galaxy would need to have a truly prodigious mass. The Schwarzschild radius Rs for a mass M is: Rs = 2*M*G/c^2 If the galaxy disk has a radius of about 50,000 LY, then the mass of the galaxy would have to be on the order of 1.6x10^17 solar masses. Estimates for the number of stars in the galaxy have an upper limit of about 2x10^11 stars. No one would credit an amount of dark matter some 10^5 times that of ordinary matter. Next, inside an event horizon, all matter must follow trajectories that end in the central singularity. That means that there would be no stable spiral arms (they would collapse into the center), and no stars could follow a path that leads it outwards from the center. Yet we observe stars within our galaxy with velocities that take them outwards. Further, the "problem" of flattened velocity curves exists for other galaxies as well. Since we can observe their stars, they can't be hidden behind an event horizon. |
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