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Fraser
2005-Feb-10, 05:07 PM
SUMMARY: Astronomers have known for a few years now that there's a direct connection between the size of a galaxy and the supermassive black hole that lurks at its centre - but they haven't been sure why this relationship exists. A new computer simulation from the Max Planck Institute has shown that growing black holes release a blast of powerful energy that actually regulates the amount of star formation in the galaxy. The bigger the galaxy, the longer this takes to happen, so the black hole can become larger.

View full article (http://www.universetoday.com/am/publish/black_holes_manage_growth.html)

What do you think about this story? Post your comments below.

greenone
2005-Feb-10, 05:33 PM
this phenomenon is remarkably similar to an accretion disk around a newly forming star. the pulsar phase of the black hole is analogus to the ignition of a protostar and the commencement of it's solar wind. both act to blow gas away from the center of the system.

i once had a professor that was fond of saying that "everything in life is cyclical" and every day since this has seemed more true.

wstevenbrown
2005-Feb-10, 05:45 PM
There are two caveats that ought to be kept in mind regarding this article. The first is a pet peeve of mine, the implication that the black holes merge as a result of gravitation alone. I realize that the article does not say this explicitly, but ANY time they talk about mergers, they ought to specify that with gravity alone, the odds against a merger of two very compact objects are trillions to one. The perceived 'spiralling in" that gets mentioned so often (elsewhere) is the result of outside forces perturbing the orbits-- in this case, friction between the accretion discs, decreasing the size of the mutual orbit, and increasing the odds of a collision.

My second concern is that the model under discussion only covers galaxies whose brightness gradients (and mass distributions) are in some sense normal. I very seriously doubt that the model covers dwarf irregulars, or low surface brightness galaxies, which may have formed from local eddies without the presence of a BH to enhance the process of star formation. S

antoniseb
2005-Feb-10, 06:07 PM
Originally posted by wstevenbrown@Feb 10 2005, 05:45 PM
I very seriously doubt that the model covers dwarf irregulars, or low surface brightness galaxies, which may have formed from local eddies without the presence of a BH to enhance the process of star formation.
I certainly agree about the dwarf irregulars. Any "galaxy" perhaps such as the LMC and SMC which are debris from a near collision of two galaxies [MW & M31 in this case] have no need for a central black hole to have been part of their formation process.

However there does seem to be a pretty consistant thousand to one ratio between central black hole mass and central bulge mass across a wide range of objects from globular clusters and intermediate mass black holes up to monsters like M87.

Generally this is another study about something that will become an increasingly important topic as we learn more about the formation of galaxies and quasars.