The ground-breaking study, published in the Nature Astronomy journal on Monday, was the result of international cooperation which included astronomers from the Dutch national observator ASTRON and UQ astronomer Dr Benjamin Pope.
The team made the discovery using the Low Frequency Array (LOFAR) radio telescope situated in the Netherlands, which as the world's largest radio telescope of its kind covers an area of about 300,000 square metres.
"This discovery is an important step for radio astronomy and could potentially lead to the discovery of planets throughout the galaxy," Pope said.
"We've long known that the planets of our own solar system emit powerful radio waves as their magnetic fields interact with the solar wind, but radio signals from planets outside our solar system had yet to be picked up," he said.
The discovery was made when the researchers found that older, otherwise magnetically inactive, red dwarf stars were still emitting radio waves.
"We've discovered signals from 19 distant red dwarf stars, four of which are best explained by the existence of planets orbiting them."
Lead author on the study Joseph Callingham from ASTRON said he and the team were confident that the signals were a sign of magnetic connection between stars and the otherwise unseen planets that orbit them.
"Our own Earth has aurorae, commonly recognised here as the northern and southern lights, that also emit powerful radio waves - this is from the interaction of the planet's magnetic field with the solar wind," Callingham said.
The discovery is just the tip of the iceberg of radio astronomy. Pope said further investigation would focus on confirming and analysing these new planets, some as far as 165 light years away.
"Follow-up observations have ruled out planets more massive than Earth, but there's nothing to say that a smaller planet wouldn't do this."