Eotvos, not Newton

I happened to run across a news story which said that scientists had found, from
studies of a distant pulsar, that the gravitational constant was the same for
that pulsar as it is on Earth.

This puzzled me, as the article gave no details, other than a reference to the
"relativistic Shapiro delay", as to how this result was obtained. It was unclear
to me what independent, and reasonably precise, information on the masses of the
components of a pulsar system - the pulsar was in a 68-day orbit around a white
dwarf - an astronomer could obtain, in addition to the data from their
gravitational behavior.

However, I was able to locate the original paper:

http://arxiv.org/abs/astro-ph/0410488

and it turned out that what the studies of the pulsar had found evidence for was
something that it was much more plausible that they could achieve.

What they found was that gravitational self-energy adds mass, by the E=mc^2
relationship, to bodies in the same manner as any other energy. This is known as
the "Strong Equivalence Principle", and accounts for the non-linearity of General
Relativity.

John Savard