We pose a new problem of collinear central configurations in Newtonian $n$-body problem. It is known that the configuration of two bodies moving along the Newtonian force is always a collinear central configuration. Can we add new two bodies on the straight line of initial two bodies without changing the move of the initial two bodies and the configuration of the four bodies is central, too? We call it 2+2 Moulton configuration. We find three special solutions to this problem and find each mass of new two bodies is zero.
"2+2 Moulton Configuration." J. Geom. Symmetry Phys. 45 95 - 110, 2017. https://doi.org/10.7546/jgsp-45-2017-95-110