Yes, dark matter does couple gravitationally with normal matter, hence can lose energy. Also, it might couple via the "weak force" which perhaps could allow it to be detected. Trouble is, both the weak force and gravity are very weak interactions so such losses are very small and low rate.. ----- I think that "Moffat gravity" and "Bekenstein gravity" would explain the latest local measurements which find no dark matter in our vicinity (they are rather ad hoc theories of gravity a good deal more complicated than Einstein/Newton but whose goal is to explain the dark matter gravitational effects without needing dark matter to exist). The observational paper, by the way, is C. Moni Bidin, G. Carraro, R.A. Mendez, R. Smith: Kinematical and chemical vertical structure of the Galactic thick disk II. A lack of dark matter in the solar neighborhood, http://arxiv.org/abs/1204.3924 17 April 2012, accepted Astrophysical Journal. "We estimated the dynamical surface mass density Sigma at the solar position between Z=1.5 and 4 kpc from the Galactic plane, as inferred from the kinematics of thick disk stars. The formulation is exact within the limit of validity of a few basic assumptions. The resulting trend of Sigma(Z) matches the expectations of visible mass alone, and no dark component is required to account for the observations. We extrapolate a dark matter (DM) density in the solar neighborhood of 0+-1 M_sun/pc^3, and all the current models of a spherical DM halo are excluded at a confidence level higher than 4sigma..." However there is another paper I.D. Karachentsev: Missing Dark Matter in the Local Universe, Astrophysical Bulletin 67,2 (2012) 123-134 http://arxiv.org/abs/1204.3377 "A sample of 11 thousand galaxies with radial velocities < 3500 km/s is used to study the features of the local distribution of luminous (stellar) and dark matter within a sphere of radius of around 50 Mpc around us... missing dark matter." which it seems to me devastates ALL THREE: Einstein+Dark matter, Moffat, and Bekenstein gravity -- if this is believed it seems to me all 3 theories of gravity must be false. And here is a somewhat ranty 50 page review paper: Pavel Kroupa: The dark matter crisis: falsification of the current standard model of cosmology http://arxiv.org/abs/1204.2546 which seems to think Einstein gravity + dark matter is clearly busted. So it seems to me that gravity must be much more complicated than (almost) everybody thought, OR these observationists are making huge mistakes. I'd like to know which.