Melbourne, Feb 2 (IANS): Some galaxies die early because they expel the gas needed to make new stars early, suggests a study.

There are two main types of galaxies, 'blue' galaxies that are still actively making new stars and 'red' galaxies that have stopped growing, said astrophysicist Ivy Wong from the University of Western Australia.

Most galaxies transition from blue to 'red and dead' slowly after two billion years or more, but some transition suddenly after less than a billion years - young in cosmic terms.

The researchers looked for the first time at four galaxies on the cusp of their star formation shutting down, each at a different stage in the transition.

Galaxies approaching the end of their star formation phase had expelled most of their gas, the findings showed.

It is unclear why the gas was being expelled. "One possibility is that it could be blown out by the galaxy's supermassive black hole," Wong noted.

"Another possibility is that the gas could be ripped out by a neighbouring galaxy, although the galaxies in the pilot project are all isolated and don't appear to have others nearby," she added.

The study appeared in the journal Monthly Notices of the Royal Astronomical Society.