From: utzoo!decvax!cca!Wedekind.ES@PARC-MAXC@sri-unix
Newsgroups: net.space
Title: Supernova, Gravity, Etc
Article-I.D.: sri-unix.2575
Posted: Mon Aug  9 11:32:18 1982
Received: Tue Aug 10 02:33:32 1982

	This is in response to Mike Knudsen' comment that a supernova's
center of mass (more precisely, the path that the center of mass follows)
remains unchanged by the explosion.

	This doesn't mean that the gravitational force on external bodies
remains unchanged.

	The gravitational force DOES stay the same in the special case where
the exploding mass retains a spherically symmetrical density, as Newton first
showed.  In particular, it's the same as if all the mass were at the CM.

	But in the general case it can get bigger or smaller, and change
direction too.  You can see all this if you imagine simple cases (where the
star splits in half, for instance, and one half lands on your doorstep!).
The galaxies where we see jets shooting off across the line of sight - they're
not pulling on us quite as hard as they used to.  This isn't surprising, since
CM is linear with position and gravity force isn't.

						cheers,
							Jerry