Stupid question about Zarya's ultimate. So, every hero has an ultimate that makes or breaks them in some cases. Genji has his dragonblade, he summons the dragons and his sword ( I don't know the name of his weapon). Reinhardt hits his hammer on the ground and breaks the surface. Tracer sends out a bomb that detonates quickly and sticks onto the target. Then we get to Zarya and her graviton surge.   


But what is her ultimate? Is it a black hole that sucks people in, I don't understand what it is and how it works. I'm not asking for a full-blown calculus explanation, but a couple of sentences explaining it would be very helpful. Thanks.