Donald Lynden-Bell
Inst. Astron., Univ. Cambridge (IoA) (Cambridge, Royaume-Uni)
Salle des séminaires Évry Schatzman, Institut d'Astrophysique de Paris
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| « Magnetic jets from swirling disks » |
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Donald Lynden-Bell |
| Jets occur all over astronomy from radio galaxies and quasars to young stellar objects to mass exchanging binaries, planetary nebulae, and other dying stars and probably in gamma-ray bursts. In most if not all of these objects there are swirling accretion disks. In any swirling disk any radial magnetic field is wound ever more tightly by differential rotation until it is strong enough to arch up out of the disk allowing the material to run back down to the disk. Thus swirling disks are accompanied by fields that arch out of the disk which have footpoints at different radii on the disk. Starting from very simple models we show how force-free magnetic fields in the presence of a weak external coronal pressure generate magnetic towers whose height grows with every turn of the accretion disk. It is shown that these towers start growing at a velocity similar to the maximum rotation speed of the disk but that they accelerate as they get to regions of lower pressure. When they are no longer pressure confined, the density of the surrounding medium provides inertial confinement provided it falls less rapidly than z^-6. It is suggested that almost all astronomical jets are generated by this process. |
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vendredi 3 mars 2006 - 11:00 Salle des séminaires Évry Schatzman, Institut d'Astrophysique de Paris |
| Page web du séminaire / Seminar's webpage |