Changes between Version 3 and Version 4 of u/u/erica/BEPaper

Timestamp:

12/19/12 15:00:13 (12 years ago)

Author:

Erica Kaminski

Comment:

—

u/u/erica/BEPaper

@@ -5 +5 @@
 While the collapse of a BE sphere has been studied extensively over the years, the literature reveals studies of the BE sphere in precarious and unphysical conditions. The BE sphere has largely been modeled as residing in low density ambient mediums (cite), seemingly to isolate the collapse of the sphere from the ambient environment. In this way, previous models have been physically unrealistic; any actual collapsing cloud of gas would not be discontinuous from the ambient medium. However, modeling the cloud in this way did reveal a feature of the collapse that was unexpected.
 
-The collapse of a BE sphere was originally anticipated to be an inside-out process, a characteristic feature of Frank Shu’s similarity solution for the Singular Isothermal Sphere (SIS). In his (1977) pivotal paper, Shu speculated that the collapse of any hydrostatic isothermal sphere, including Bonnor Ebert spheres, would approach the SIS through a subsonic adjustment to 1/r^2 density distribution. The classic  inside-out collapse of the SIS was then, as Shu proposed, a general feature of collapse, applicable to any hydrostatic isothermal sphere, unstable or not. 
+The collapse of a BE sphere was originally anticipated to be an inside-out process, a characteristic feature of Frank Shu’s similarity solution for the Singular Isothermal Sphere (SIS). In his (1977) pivotal paper, Shu speculated that the collapse of any hydrostatic isothermal sphere, including Bonnor Ebert spheres, would approach the SIS through a subsonic adjustment to 1/r^2^ density distribution. The classic  inside-out collapse of the SIS was then, as Shu proposed, a general feature of collapse, applicable to any hydrostatic isothermal sphere, unstable or not. 
+
 Simulations of stable, flat-topped BE spheres in low density ambient environments, however, proved the contrary. In 1994 Foster and Chevalier explored the collapse of BE spheres of varying truncation radii embedded in ambient backgrounds of uniform rho = 0.01 rho(RBE), where Rbe is the BE sphere’s truncation radius. Their set ups showed that despite initial perturbation methods, as well as whether the sphere was initially in a stable or unstable hydrostatic regime, the collapse proceeded much differently than the SIS. Instead of an inside-out collapse, the collapse of a flat-topped BE sphere was outside-in. Further, the collapse was not subsonic, rather supersonic. This directly refuted Shu’s proposal that the collapse is generally inside-out. (note - the sink formation in the flat-topped studies may more closely resemble the collapse of the SIS... perhaps this is what he was talking about?). Studies of the collapse with more sophisticated fluid dynamic codes have provided  further support of  outside-in collapse of the BE sphere (B&P).