http://oklo.org/2006/04/15/q/ characterizing planetary systems Fri, 18 Nov 2011 22:27:52 +0000 hourly 1 http://wordpress.org/?v=3.2.1 http://oklo.org/2006/04/15/q/comment-page-1/#comment-1250 Centauri Dreams » Blog Archive » Hyades Planet Challenges Formation Theories Wed, 21 Feb 2007 15:09:35 +0000 http://oklo.org/?p=39#comment-1250 [...] Laughlin is saying that the likely dispersal of the protostellar disks in the Hyades stars (thanks to UV) makes core accretion less likely in the case of Epsilon Tauri b (there simply wasn’t time). Whereas if gravitational instability produces a planet for every few hundred stars formed, as Laughlin believes, then there is no reason not to expect such a world in an open cluster like the Hyades. That’s a win for gravitational instability, though Laughlin still sees core accretion as the dominant model, writing elsewhere that “…the weight of observational and theoretical evidence seems to be shifting against the gravitational instability hypothesis.” [...] [...] Laughlin is saying that the likely dispersal of the protostellar disks in the Hyades stars (thanks to UV) makes core accretion less likely in the case of Epsilon Tauri b (there simply wasn’t time). Whereas if gravitational instability produces a planet for every few hundred stars formed, as Laughlin believes, then there is no reason not to expect such a world in an open cluster like the Hyades. That’s a win for gravitational instability, though Laughlin still sees core accretion as the dominant model, writing elsewhere that “…the weight of observational and theoretical evidence seems to be shifting against the gravitational instability hypothesis.” [...]

]]> http://oklo.org/2006/04/15/q/comment-page-1/#comment-1107 systemic - Lonely Planet Guide to the Hyades Fri, 09 Feb 2007 07:49:58 +0000 http://oklo.org/?p=39#comment-1107 [...] For more information, this series: 1, 2, 3, 4 and 5, 6, and 7. of oklo posts that compare and contrast the gravitational instability and core accretion theories for giant planet formation. [...] [...] For more information, this series: 1, 2, 3, 4 and 5, 6, and 7. of oklo posts that compare and contrast the gravitational instability and core accretion theories for giant planet formation. [...]

]]> http://oklo.org/2006/04/15/q/comment-page-1/#comment-100 systemic - G.I. No Tue, 02 May 2006 02:28:25 +0000 http://oklo.org/?p=39#comment-100 [...] (1) In order to have gravitational instability work in the manner shown in the fragmentation simulations, you need to start with an axisymmetric disk that has a sufficiently low value for the Toomre Q parameter. That is, in order for the initial conditions in the successful Boss simulations to be valid, a growing protostellar disk needs to remain completely stable with respect to low-level non-axisymmetric disturbances until BOOM, it reaches a threshold Q value where it is prone to spiral instabilities that exponentiate on a near-orbital timescale. [...] [...] (1) In order to have gravitational instability work in the manner shown in the fragmentation simulations, you need to start with an axisymmetric disk that has a sufficiently low value for the Toomre Q parameter. That is, in order for the initial conditions in the successful Boss simulations to be valid, a growing protostellar disk needs to remain completely stable with respect to low-level non-axisymmetric disturbances until BOOM, it reaches a threshold Q value where it is prone to spiral instabilities that exponentiate on a near-orbital timescale. [...]

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