2004ApJ...614..914A

In a relativistic model of a neutron star, the star's mass is less than the mass of the individual component baryons, because the star's negative binding energy makes a contribution to the star's total energy and its mass. A consequence of this relativistic mass deficit is that a neutron star that is accreting matter increases its mass at a rate that is slower than the mass of a baryon times the rate that baryons are accreted. This difference in the rate of change of the masses has a simple relation with the star's gravitational redshift. We show that this effect has the potential to be observed in binaries where the mass transfer is driven by angular momentum losses from the gravitational radiation emitted by the binary motion, if the physics of the donor star is understood well enough.