LRC.Slocum@UTEXAS-20@sri-unix (08/06/82)
From: Jonathan Slocum <LRC.Slocum at UTEXAS-20> First of all, I'm not sure what "Supernovas blow away NONE of the stellar mass" was supposed to mean. Second, let me apologize in advance for the length of this msg; but we're dealing with a complicated subject which folks have been discussing at different levels without realizing it. So... The debate about how much mass is ejected was originally inspired by the question of how much mass was left behind, compared to the original mass, in an effort to guesstimate the observable gravitational effects. Bearing that in mind, and bearing in mind that astronomers recognize FIVE different types of supernovas, we have the following generalization: A small, small portion of the original star's mass is converted into energy in a couple of weeks' time; the star may radiate more energy than several times 10^9 suns. (Planets within a hundred light-years or so will become [almost] sterile.) The radiation pressure of this conversion is what compacts the central mass, and blows away the rest. The "central" remnant of a supernova will usually be a neutron star -- this is how these things get created. A supernova ejects a large portion of the star's original mass -- somewhere in the region of 85% give or take plenty. Therefore, in theory, a change in gravitational WAVE effects will be measurable one light-time after the event (some mass has been lost; far more, shuffled around). However, the gravitational ATTRACTION exerted by the star at that time is altered only according to the amount of mass that was lost by virtue of being converted into energy (and which has passed the observation point), and according to any asymmetry that may have developed in the ejecta shell. These changes are, practically speaking, negligible. Only over a LONG period of time will the attraction change -- depending on the asymmetry of the ejecta shell and whether any of it has passed the measurement point. Now, these babies tend to go off a LONG way away (thank goodness!) -- so far away that there is no hope of measuring the very, very slight displacements that take place. If I remember right, none have occured in our galaxy since 1754. And, to add more context, the "official" distance of the Andromeda galaxy was in recent history doubled -- from 1 to 2 million light years -- due to revised measurement techniques. Even in theory, measuring the displacement requires -- need I say it? -- that one know the ORIGINAL position AND velocity vector of the object being observed; therefore, it thus requires that one have a LONG time baseline, since the supernova's shell expands [by interstellar standards] very slowly. Ergo, we will not be observing any such displacements very soon. -------