The real estate in our corner of the universe suddenly seems so much bigger. Australian astronomers are among an international team that has announced the discovery of 28 more planets in our galaxy.

Spotted in the past year, they raise the number of worlds known to circle other stars to 236 - a 12 per cent increase.

Although most of the new finds are probably giant balls of gas, more like Jupiter than Earth, the leader of the Australian team, Chris Tinney, said the increasing pace of discovery strongly boosted chances that the galaxy was swarming with much smaller, rocky and potentially habitable worlds too small to detect with existing technology.

"The more we look, the more we find planets," said the University of NSW astronomer whose team used the Anglo-Australian Observatory near Coonabarabran to find "four or five" of the 28.

"Something like 10 to 15 per cent of stars host gas giants. A larger fraction of stars may host planets too small for us to detect."

The astronomers, who used telescopes in Hawaii and California, also found seven brown dwarfs - objects too small to become stars, but too big to be called planets.

"Brown dwarfs are little stars that couldn't," said Dr Tinney. "They never got big enough to ignite their nuclear fuel."

Another two objects are "borderline" - either very large planets or small brown dwarfs.

Among the 28 new worlds, found by watching the way their gravitational pull tugs their parent stars from side to side, are at least four new multiple-planet systems. "It's been a bumper vintage," said Dr Tinney.