In this simulation of three gravitating Newtonian particles, a blue "planet" orbits a red "star" until they meet the "dark star." The physics is simple, yet the numerical behavior is extreme. Indeed, Mathcad's numerical integrators have difficulty modeling the motions correctly.
Solution is sensitive to the choosing numerical methods for solving
Same initial condition but the method is not RADAU (see the first video) but Adams/BDF:
Radau and Adams/BDF Methods of the ODE solution on the one plot:
Radau and Adptive Methods of the ODE solution on the one plot:
Mathcad Prime - with units but without animation
I think it is the Adams/BDF method of ODE solution.
Radau and Fixed Methods of the ODE solution on the one plot: