The name has been coined for the discovery of miniature galaxies whose stars have been compressed together in an volume previously thought impossibly small, Britain's Royal Astronomical Society (RAS) said.

A British-led team discovered half a dozen UCDs in the Fornax galaxy cluster in 2000, using the Anglo-Australian Telescope in Australia.

Followup observations, using the Hubble orbiting space telescope and the European Southern Observatory's Very Large Telescope in Chile, showed that this phenomenon was very strange, the RAS said in a press release.

"Athough their masses are similar to those previously known dwarf galaxes, [UCDs] are amazingly small -- only about 120 light years across," it said.

"Tens of millions of stars are squashed into what is a tiny volume by galaxy standards."

The research into UCDs was unveiled by University of Bristol astronomer Steve Phillipps at the the RAS' National Astronomy Meeting at the Open University, central England, on Thursday.

Phillipps' team have found a total of 52 UCDs in Fornax and eight in the Virgo galactic cluster, also around 60 million light years away.

He theorises that UCDs are the core remnants of very old galaxies that originally were larger and have been stripped of their outer stars.

Explanation of terms:

- An EVENT HORIZON is the gravity field of a black hole where the gravitational pull is so big that nothing can escape, not even light.

- REDSHIFT is the stretching of a wavelength in the radioactive part of the energy spectrum. Sources of light that are receding have more of their light in in longer (redder) wavelengths. Measuring the redshift of stars is a means of gauging the expansion of the Universe.

- WIMPZILLAS are massive versions of large weakly interacting massive particles (WIMPS). Both Wimpzillas and WIMPS are theoretical particles whose existence was mooted by some physicists to explain DARK MATTER, an enigmatic, invisible force that keeps galaxies together and explains the missing mass of the Universe.

SPACE.WIRE