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Black hole mass-sigma correlation
A BBC Horizon program described the correlation found between the galaxy
hub black hole mass and the "sigma", the speed of the stars in the outer regions of the galaxy. One thing that confuses me, would not the speed of the stars in a galaxy also follow a distance from center relation as that of planets around a star? Hans Aberg * Anti-spam: remove "remove." from email address. * Email: Hans Aberg * Home Page: http://www.math.su.se/~haberg/ * AMS member listing: http://www.ams.org/cml/ |
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Black hole mass-sigma correlation
In message , Hans Aberg
writes A BBC Horizon program described the correlation found between the galaxy hub black hole mass and the "sigma", the speed of the stars in the outer regions of the galaxy. One thing that confuses me, would not the speed of the stars in a galaxy also follow a distance from center relation as that of planets around a star? In "Wrinkles in Time" George Smoot writes that Vera Rubin and Kent Ford published a paper in 1978 showing that galaxies _don't_ obey Kepler's third law - beyond a certain distance, the rotational velocity of stars is almost constant. That's when dark matter became fashionable, though apparently it "should" have happened much earlier. -- "Roads in space for rockets to travel....four-dimensional roads, curving with relativity" Mail to jsilverlight AT merseia.fsnet.co.uk is welcome. Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk |
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Black hole mass-sigma correlation
In message , Hans Aberg
writes A BBC Horizon program described the correlation found between the galaxy hub black hole mass and the "sigma", the speed of the stars in the outer regions of the galaxy. One thing that confuses me, would not the speed of the stars in a galaxy also follow a distance from center relation as that of planets around a star? In "Wrinkles in Time" George Smoot writes that Vera Rubin and Kent Ford published a paper in 1978 showing that galaxies _don't_ obey Kepler's third law - beyond a certain distance, the rotational velocity of stars is almost constant. That's when dark matter became fashionable, though apparently it "should" have happened much earlier. -- "Roads in space for rockets to travel....four-dimensional roads, curving with relativity" Mail to jsilverlight AT merseia.fsnet.co.uk is welcome. Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk |
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Black hole mass-sigma correlation
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Black hole mass-sigma correlation
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Black hole mass-sigma correlation
Thanks for the replies. I suspected that the galaxy mass might have
something to do with the its stars not obeying the Kepler law. But if the outer galaxy stars do not do that, what are their movements, generally faster or slower than the Kepler law? Or perhaps there are some stars in the outer regions that do not move in circular orbit around the galaxy center at all? Hans Aberg * Anti-spam: remove "remove." from email address. * Email: Hans Aberg * Home Page: http://www.math.su.se/~haberg/ * AMS member listing: http://www.ams.org/cml/ |
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Black hole mass-sigma correlation
Thanks for the replies. I suspected that the galaxy mass might have
something to do with the its stars not obeying the Kepler law. But if the outer galaxy stars do not do that, what are their movements, generally faster or slower than the Kepler law? Or perhaps there are some stars in the outer regions that do not move in circular orbit around the galaxy center at all? Hans Aberg * Anti-spam: remove "remove." from email address. * Email: Hans Aberg * Home Page: http://www.math.su.se/~haberg/ * AMS member listing: http://www.ams.org/cml/ |
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Black hole mass-sigma correlation
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Black hole mass-sigma correlation
Hans Aberg wrote:
Only approximately, as there is a GR correction showing that they will in fact slowly drop into the center (due to emission of "gravity waves"). This is also why this development is so exiting: As GR, unlike Newtonian physics, predicts that the galaxy mass should drop into the center, one would think that the belief that there are black holes at the centers of the galaxies should have come along very early, but in fact it took a long time. Now there are even formulas for telling the size of that black hole mass. This effect should be completely negligible compared to other effects taking place in a galaxy, such as the transport of angular momentum by the spiral arms, which may let some of the material in the galactic disc drift inwards while angular momentum is transported outwards, and the scattering of stars against giant molecular clouds. There may be even more dramatic effects taking place during the formation of a galaxy, and as far as we can tell today the black holes at the centers of the galaxies form early in the life of the galaxies. Angular momentum loss through the emission of gravitational waves can be important in the evolution of close binaries though, and provides a perfect explanation for the timings of the double pulsar PSR 1916+13. Ulf Torkelsson [Mod. note: reformatted to 80 characters per line -- mjh] |
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