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From: matt@utastro.UUCP (Matt Wood)
Newsgroups: net.physics
Subject: Re: A Thought Experiment (Supernova)
Message-ID: <337@utastro.UUCP>
Date: Thu, 6-Feb-86 12:21:36 EST
Article-I.D.: utastro.337
Posted: Thu Feb  6 12:21:36 1986
Date-Received: Fri, 7-Feb-86 21:31:45 EST
References: <2026@teddy.UUCP>
Distribution: net
Organization: U. Texas, Astronomy, Austin, TX
Lines: 37
Summary: blinded by the light

In article <2026@teddy.UUCP>, srk@teddy.UUCP writes:
> Assume there are two stars, A and B, of equal mass.  They are close enough to
> have significant gravitational attraction, but far enough apart that it takes
> light a week or two to travel from one to the other.  They are not in mutual
> orbit but are approaching each other head on.  This is obviously not a stable
> situation!
> 
> Star B undergoes supernova.
> 
> At a safe distance, equidistant from both A and B, is an observer who decides
> to measure these two stars immediately after the light from the supernova
> passes his planet (he was watching a soap opera at the time...).  He measures
> the mass and acceleration of both stars.
> 
> What will he see?
> 
While the supernova is bright, it will shine about as brightly as the rest
of the stars in the galaxy.  A "safe distance" from such an event is about
10 light years, so if the stars a one light week apart, 
he'd probably see a single point of light.
Now if we assume that we've got this great shielding on our ship and could
get in close (~1 light year, this would give us good angular resolution),
then roughly one year and 1 month after the explosion we'd see this shell
of gas racing towards us at ~30,000 km/s.  

Seriously though, Ethan Vishniac gave you the theoretically-"correct"
answer that I'll bet you were looking for, that ejecta already past
star A will no longer affect the mechanics of the system.  In fact,
since after a year we'll observe the ejecta to be well past star A,
we might note that A is no longer accelerating at all
noticably, unless B left behind a newborn neutron star.

-- 
		Matt A. Wood 
		Astronomy Dept, University of Texas, Austin TX 78712  
		{allegra,ihnp4}!{ut-sally,noao}!utastro!matt	(UUCP)
		matt@astro.UTEXAS.EDU.				(Internet)