Instead of creating new stars, the universe's huge galaxies tend to expand by colliding with smaller galaxies and assimilating the mass of their neighbors, according to a new study by scientists in Australia.

That means in approximately five billion years, the nearby massive galaxy Andromeda will merge with our own galaxy, the Milky Way, "in an act of galactic cannibalism," said the scientists in a news release.

Not only that, gravitational pull is expected -- in many, many billions of years -- to eventually cause all the galaxies in bound groups and clusters to combine into a few super-giant galaxies.

"If you waited a really, really, really long time that would eventually happen ... but by really long, I mean many times the age of the universe so far," research lead Aaron Robotham, who is based at the University of Western Australia node of the International Centre for Radio Astronomy Research, said in a statement.

Findings from the work have been published in the scientific journal Monthly Notices of the Royal Astronomical Society and a video simulation of the Andromeda-Milky Way smash-up has been developed by the scientist involved with the new analysis and posted on YouTube (but also inserted at the end of this story).

Astronomers looked at more than 22,000 galaxies and determined while smaller galaxies appear quite efficient at creating new stars from gas and stardust, the biggest galaxies around are much less successful at forming stars -- hardly producing any new stars themselves, as a matter of fact.

"All galaxies start off small and grow by collecting gas and quite efficiently turning it into stars," but over time smaller galaxies end up lost to their larger counterparts, Robotham said. "Every now and then they get completely cannibalized by some much larger galaxy."

Our own galaxy in fact is at a tipping point where it is expected to mainly grow in the future by eating smaller galaxies, he added.

"The Milky Way hasn't merged with another large galaxy for a long time but you can still see remnants of all the old galaxies we've cannibalized," he said. "We're also going to eat two nearby dwarf galaxies, the Large and Small Magellanic Clouds, in about four billion years."

Then, about a billion years after that, the Milky Way and Andromeda will merge.

"Technically, Andromeda will eat us because it's the more massive one," Robotham said.

Robotham said as galaxies grow, they develop a stronger gravitational field and can therefore pull in adjacent galaxies more easily.

Likewise, star formation slows down in the really big galaxies because of extreme feedback events in a very bright region at the center of a galaxy -- known as an active galactic nucleus.

"The topic is much debated, but a popular mechanism is where the active galactic nucleus basically cooks the gas and prevents it from cooling down to form stars," Robotham said.

A majority of the data for the research was collected with the Anglo-Australian Telescope in New South Wales as part of the Galaxy And Mass Assembly survey, which involved more than 90 scientists and took seven years to complete. This study is one of over 60 publications to have come from the work, with another 180 still on the way.