A landmark Australian-led survey of more than 3000 galaxies may help answer why they can look so different, why they spin in different directions and what stops them from forming new stars.
The study, which began in 2013, used a custom-built spectrograph - which photographs light spectra or colours - connected to a four-metre telescope at Siding Spring Observatory in NSW.
Observing 13 galaxies at a time, the researchers soon built up a snapshot of multiple points in 3068 galaxies.
The final data paper, released on Wednesday, included reports from 41 authors from Australia, Belgium, the US, Germany, Britain, Spain and The Netherlands.
The results have already allowed astronomers from around the world to explore how galaxies interact with each other, and how they grow, speed up or slow down over time.
"The nature of galaxies depends both on how massive they are and their environment," said lead author and University of Sydney Professor Scott Croom.
"For example, they can be lonely in voids, or crowded into the dense heart of galactic clusters, or anywhere in between.
"The survey shows how the internal structure of galaxies is related to their mass and environment at the same time, so we can understand how these things influence each other."
The data has already spurred some unexpected findings.
One group of astronomers showed that the direction of a galaxy's spin depends on the other galaxies around it, and changes depending on the galaxy's size.
Another group showed galaxies that were winding down star-making began that process only a billion years after they drifted into the dense inner-city regions of galaxy clusters.
"The survey is finished now, but by making it all public we hope that the data will continue to bear fruit for many, many years to come," Dr Croom said.