The vast Universe.
The immense Galaxy Nebula and Andromeda Nebula have collided.
The initial point of intersection and collision was at the outermost arms of the two giant nebulae.
These two arms, each thousands of light-years wide, are loaded with a large number of stars, planets, asteroids, interstellar dust...
Although these materials are far enough from each other not to collide easily and are always rotating at high speeds around the center of their respective giant nebulae, as the two giant nebulae begin to make contact, their arms also start to collide in opposite directions.
From the cosmic perspective, the two arms look like two sparse arc-shaped beams, fiercely colliding.
It's important to note that since the arms are not straight and follow elliptical orbits, the actual collision surface is the curved side, not the tail end.
To be precise, it's the intersection and friction of two arc-shaped arms.
