🚀 go-pugleaf

In article <3342EBCB.6677@boeing.com>, Fred McGalliard
<frederick.b.mcgalliard@boeing.com> wrote:

> Chris Wagner wrote:
> 
> (a nice description of rest and relative mass. Thanks Chris.)
> 
> But now I would like to take this a few steps deeper. What mass do I
> deal with when the object is a collection of confined photons, and
> possibly some neutrinos. The rest mass of a confined photon should be
> it's ordinary mass, or just it's energy, eh? The gravitational mass of a
> star then is (a bunch of stuff) + (the mass of the confined photons).
> When the confined photons go streaming off to infinity, they can leave
> as much as all of their mass/energy behind. Where is it? How is it left
> behind?

Photons do not have a rest mass.  They have an energy equal to Planck's
constant time the speed of light divided by their wavelength, but no
mass.  This is *equialent* to a mass, and produces gravitational
attraction, but a photon travels at the speed of light in all reference
frames - thus it is never at rest in your reference frame - thus it never
has a rest mass.

The gravitational mass of a star = the mass of all the matter + the mass
equivalence of all the free energy.

When a photon goes screaming off to infinity, it carries its energy, and
the equivalent gravitational attraction, with it.  Nothing is left behind
in the star except fusion products lighter than the original fuel; the
star is now a tiny bit less massive than before.

William J. Keith