The galaxies - classed as "dwarves" because they contain relatively few stars - have been named Antlia and Argo by the Cambridge-based scientists. They went unnoticed before because their low star count and lack of activity meant they did not show up in observations.
Yet Mike Irwin of the Royal Greenwich Observatory, who led the research, believes the findings could hold the key to many mysteries about the formation and structure of the universe.
He told the National Astronomical Meeting in Southampton: "Despite their unassuming appearance, dwarf galaxies hold the key to many questions about the formation, structure and evolution of galaxies."
George Hau, who discovered the galaxies with Alan Whiting at the Institute of Astronomy, said: "The universe may be full of galaxies like this. It may be that our galaxy, the Milky Way, is unrepresentative of the majority."
As with previous papers presented to the meeting this week, the galaxies could offer important clues to one of the most important questions facing astronomers - the form and distribution of the invisible "dark matter" that is reckoned to make up more than 90 per cent of the universe's mass. "If we discover more like this it will help us understand the nature of dark matter and the age of the universe," said Mr Hau.
Antlia, about three million light-years from Earth, has a diameter of between 4,000 and 6,000 light years and is reckoned to contain a million stars. By comparison, our own Milky Way has a radius of 100,000 light years and contains about 200 billion stars.
Antlia is so distant from other, bigger galaxies that it will have escaped been "stretched out" by their gravitational forces, Dr Irwin explained.
Argo, while closer to its local group neighbours than Antlia, is also in an area of space previously thought to be fairly empty. It is about 13 million light years away, though the team has not yet worked out how many stars it contains.Reuse content