Re: [Phys-L] TWO QUESTIONS

[David Bowman <David_Bowman@georgetowncollege.edu>]

Regarding the premise of Ludwik's questions:

> Suppose our Sun is hit by a star of equal mass, traveling in the
> opposite direction. The two stars fuse mechanically and remain
> in rest  (in the frame of their center of mass).

Since the Sun is not a binary star that means any star that hits it would be initially unbound to it.  That means the potential energy of the initial configuration would be at least that of two solar mass objects at rest asymptotically far apart.  Assuming this minimal energy configuration and assuming tidal effects do not appreciably distort either star before impact that means the moment they touch they would each be going at least about 309 km/s relative to the COM frame (618 km/s relative closing speed).  The released energy in the collision would be at least as much as 15.4 million years worth of solar radiation from one of the stars (not counting the additional released energy of reconfiguring the touching spheres into a single fused object).  I don't think I would want to be watching the collision from only 1 AU away.

Dave Bowman