I am just wondering - is space-time curvature in the presence of energy-momentum ( i.e. in interior solutions to the EFEs ) always pure Ricci in nature ? I had a discussion recently with someone who claimed that, but personally I would suspect that not to be the case in general, since I see no reason why gravitational radiation from distant sources couldn't penetrate into such regions, so that the Riemann tensor contains both Ricci and Weyl contributions. I am not completely sure though, so any input will be appreciated. I have heard of the Petrov classification scheme for space-times, which is done via Weyl scalars, but to be honest it is a little over my head. Thanks in advance.