A team of scientists led by the University of Bristol has discovered a new class of galaxy - the first such discovery since the 1930s.
The Hubble Space Telescope was used to study the seven new galaxies, which have been named ultra-compact dwarfs (UCDs).
The galaxies were discovered using the Hubble Telescope
The galaxies - in a cluster 60 million light-years away - are so small that on ordinary photographs, they look like individual stars.
Dr Steve Phillipps, joint team leader and an astrophysicist at the University of Bristol, said: "The UCDs contain tens of millions of stars, which are contained in volumes not much more than 100 light-years across.
"This makes them far smaller, and more compact, than any previously known galaxies.
"For comparison, the Milky Way, in which we live, is over 100,000 light-years in diameter.
"An entire UCD would fit comfortably in the space between the Earth and relatively nearby bright stars like Rigel or Betelgeuse in Orion," he added.
The European Southern Observatory's Very Large Telescope in Chile, was also used in the study.