Sciency Words: Supercluster

Today’s post is part of a special series here on Planet Pailly called Sciency Words. Every Friday, we take a look at a new and interesting scientific term to help us all expand our scientific vocabularies together. Today’s word is:

SUPERCLUSTER

Before we talk about superclusters, let’s talk about fruit. What is the definition of fruit? It depends on who you ask. A biologist’s answer will involve seeds and plant reproduction. A grocer’s answer will involve flavor, specifically sweet flavors. This is why tomatoes and cucumbers are fruit in biology and vegetables in grocery stores.

So knowing that there are two different definitions of fruit, let’s turn our attention to superclusters. A supercluster is a large group of galaxies. That’s the easy part of the definition. The hard part is determining where one supercluster ends and another begins.

Astronomers in Hawaii say gravitational currents determine the shape and boundaries of superclusters. Using data on the velocities of 8,000 galaxies, they’ve even mapped the currents of our own supercluster and given that supercluster a name: Laniakea (immeasurable heaven in Hawaiian).

But Gayoung Chon if the Max Plank Institute of Extraterrestrial Physics is quoted as saying, “The definition [of supercluster] you use really depends on the questions you want to ask. The latest method is a very good way to chart the large-scale structures of the Universe, but it doesn’t ask what will happen to those structures eventually.”

Gayoung Chon prefers an alternative definition: superclusters are structures that will eventually collapse into a single object. The gravitational currents of Laniakea apparently won’t cause that to happen, so Laniakea is not (according to this definition) a supercluster—just as tomatoes (according to grocers) are not sweet enough to be considered fruit.

It all depends on the questions you ask and who you’re asking.