Jonathan S. asked,

...but aren't _changes_ in gravitational
fields supposed to propagate by gravity
waves?

Yes, oscillating masses (like co-orbiting neutron stars or binary BHs)
or massive gravitational events (like a SN going off) should radiate
copious amounts of GW energy. I prefer the term 'spatial acoustic
pressure waves' propagating at c. This clarifies the distinction between
gravity and so-called 'gravity waves'. But the latter term requires an
underlying spatial medium which is a big no-no.

AFAIK the existence of gravity waves
has been fairly well confirmed by Taylor
and Hulse's binary pulsar observations,
though everyone will be happier when
direct observations are made.

Yes, Taylor & Hulse's 1974 observations indirectly inferred the pulsar's
orbit was decaying by GW radiation as Einstein had predicted 'way back
in 1915. But this newest Chandra image is showing what appears be
*direct* signature of GWs. Yet they're being pawned off as "sound" in
the rarified gas of space, since space has gotta be 'pure void'. Uh-huh.
oc

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