> This system contains a closely orbiting neutron star and a white dwarf, along with a more distant white dwarf orbiting that pair of stars. The new research found both inner stars accelerating at very similar speeds, which fits in with the equivalence principle as explained in Einstein’s general theory of relativity.
It does?
I think what they’re trying to say is that the gravitational waves given off by the system match up with what GR predicts. That’s what has been checked on other pulsar binaries. … No, I’m wrong. It seems to be saying that the orbits of the inner white dwarf and pulsar around the outer white dwarf are almost the same. This needs checking?
> our limit on the strong-field Nordtvedt parameter, which measures violation of the universality of free fall, is a factor of ten smaller than that obtained from (weak-field) Solar System tests and a factor of almost a thousand smaller than that obtained from other strong-field tests.
I’m familiar with PPN parameters, but which is the Nordtvedt parameter?
> In theoretical astrophysics, the Nordtvedt effect refers to the relative motion between the Earth and the Moon which would be observed if the gravitational self-energy of a body contributed differently to its gravitational mass than to its inertial mass.
Oh, so they’re checking the assumption that gravitational mass = inertial mass. That is important. Nordtvedt gave us all of the PPN parameters. The one most closely linked to his name is eta_n.
According to what I wrote in wikipedia, the best limit on eta_n has come from Lunar Laser Ranging and is no more than 9e-4.
The new upper bound is 2.6e-6.
Excellent. I wonder how long before somebody updates wikipedia.
For original article see https://sci-hub.tw/https://www.nature.com/articles/s41586-018-0265-1