1 hour ago, Airbrush said:

To be precise our "Local Group" is the name for our local cluster of 54 galaxies.  "Supercluster" is a word for ALL galaxies and galaxy clusters that are forever bound together by gravity.

"The Local Group is the galaxy group that includes the Milky Way. The Local Group comprises more than 54 galaxies, most of them dwarf galaxies. Between 1 billion and 1 trillion years from now, they will collide and form a single galaxy. Its gravitational center is located somewhere between the Milky Way and the Andromeda Galaxy. The Local Group has a diameter of 10 Mly (3.1 Mpc) (about 10²³ meters) and has a binary (dumbbell)^[1] distribution. The group itself is a part of the larger Virgo Supercluster, which may be a part of the Laniakea Supercluster."

https://en.wikipedia.org/wiki/Local_Group 

The Laniakea SC is not gravitationally bound.

11 minutes ago, StringJunky said:

The Laniakea SC is not gravitationally bound.

How can a supercluster NOT be gravitationally bound?  Is the Virgo Supercluster gravitationally bound forever?

14 minutes ago, Airbrush said:

How can a supercluster NOT be gravitationally bound?  Is the Virgo Supercluster gravitationally bound forever?

Its component superclusters are individually bound but not as a group.

Quote

Unlike its constituent clusters, Laniakea is not gravitationally bound and is projected to be torn apart by dark energy.[6]

https://en.wikipedia.org/wiki/Laniakea_Supercluster

I think if you look at the universe's cobwebby structure on the large scale, the web strands that the SCs make up get thinner and further apart with the expansion; the voids between the strands become larger.

Edited September 27, 20187 yr by StringJunky

1 hour ago, StringJunky said:

Its component superclusters are individually bound but not as a group.

I think if you look at the universe's cobwebby structure on the large scale, the web strands that the SCs make up get thinner and further apart with the expansion; the voids between the strands become larger.

Very interesting.  I had always assumed the word "supercluster" meant gravitationally bound.  So this means not all superclusters are bound together forever.

On the edges of any supercluster it seems to me that galaxies could orbit each other and interact in such a way that an entire galaxy could be thrown out of the supercluster, just as planets in a solar system can interact in such a way that a planet can be cast out of the solar system.  Right?

 

Edited September 27, 20187 yr by Airbrush