Allow me to paint you a quick picture. Metaphorical pictures are my speciality.. I think.
You’ve just turned off the shower. Your shower has a flat floor, yet all the leftover bubbles seem to find and stick to one another and gather around the central drain because it’s a source of gravity (humor me). As each bubble is pulled in, the trailing bubbles get pulled closer.
Okay.. now imagine our Local Group of galaxies (us, Andromeda, Triangulum), outlying and bound to the Virgo Cluster of galaxies as individual bubbles stuck to one another, moving to an unseen mass with astounding gravitational pull which, for the sake of my metaphor, is the drain. The posted chart shows distribution of mass, and the direction and flow of it’s movement towards the Attractor.
We are all moving at breakneck speeds towards this, a mere 250 million light years away. Relative to us, that’s an eternity. To the universe? That’s a strand of hair.. The attached photo shows how, like bubbles or water, we are all flowing to a massive source of gravity that we can’t see. It could be a hyper cluster of galaxies or a conglomerate of black holes. The math states it’s easily got the most mass in our neighborhood, but is very hard to see being that a large percentage of the sky we can see outside of the Milky Way is blocked by starlight and dust.
This is all due to dark matter, most likely. But dark flow, dark energy, or all three (or none) could be responsible.