The astronomy picture of the day is Laniakea, the newly discovered/defined super-structure that includes our Milky Way Galaxy. There’s already a Wikipedia entry. The massive Virgo Supercluster is now just an “appendage” in the bigger scheme of things.
It’s hard to discern shape when you’re sitting within. The thing I’ve never heard referenced is how astronomers map structure taking into account the tens and hundreds of millions of years between one end and another. Not just big space, but long stretches of time.
We’re on one side of Laniakea, but we view the other side not as it is today, but as it was almost five hundred million years ago. All galaxies are in movement relative to each other. Most are flying apart. Only close associations share a gravitational attraction. Astronomers admit the boundaries of superclusters are vague. We know, for example, the Triangulum Galaxy, imaged here by Alexander Meleg …
… is gravitationally bound to our Local Group. It’s a probable satellite of the Andromeda Galaxy. We might be colliding with that whole array in a few billion years. But will our star stuff be mixing it up with aliens on the other side of Laniakea in the endless eons to come? Who can be sure?