Imagine three marbles A, B & C with each with 2 small lasers attached. All in the same rest frame, separated from each other by a light year, and forming an isosceles triangle (where AB and AC are the same length, and the centre of BC is a kilometre from A), and that the lasers of each pointed to the marbles adjacent to them in the triangle (so like pointing to the adjacent vertices). And imagine that there were two equally sized space ships, D & E each having the external shape of of opposing halves of a cylinder bisected along its axis. D and E both travel fast towards the midpoint of BC from opposite directions along a line perpendicular to BC and which transects BC at its midpoint. Imagine that, from the perspective of D and E, that in the last 30 seconds of their journey, they decelerate as fast as the laws of physics allow and come together to form a cylinder 100m in diameter with its axis orientated along BC. I'll refer to the cylinder as F. Imagine F has enough mass to (from F's perspective) pull A towards it at a rate of 0.01 mm per second from where A was when F was formed (so the rate will increase as A gets closer). Over time A will be pulled towards F such that they touch. But what is the GR explanation using an A centred coordinate system, of the reasonably rapid close in distance between A and F. Are B and C being pulled towards A along with F, if so, how is that explained, if not, what is the explanation for the light from each still pretty much pointing at the axis of F (even when A and F touch)?