London, Feb 13 (ANI): New calculations by scientists have suggested that Ultra Compact Dwarf galaxies (UCDs), a recently discovered class of object, may have had stars packed together a thousand times more closely than in the solar neighborhood.
UCDs were discovered in 1999. Although they are still enormous by everyday standards, at about 60 light years across, they are less than 1/1000th the diameter of our own Galaxy, the Milky Way.
Astronomers believe that UCDs were created when more normal galaxies collided in the early Universe.
But oddly, UCDs clearly have more mass than the light from the stars they contain would imply.
Up to now, exotic dark matter has been suggested to explain this 'missing mass', but this is not thought to gather in sufficient quantities within a UCD.
In their research, PhD student Joerg Dabringhausen, Professor Pavel Kroupa of the University of Bonn, and their colleague Dr Holger Baumgardt, present a different explanation.
The astronomers think that at one time, each UCD had an incredibly high density of stars, with perhaps 1 million in each cubic light year of space, compared with the 1 that we see in the region of space around the Sun.
These stars would have been close enough to merge from time to time, creating many much more massive stars in their place.
These more massive stars consume hydrogen (their nuclear fuel) much more rapidly, before ending their lives in violent supernova explosions.
All that then remains is either a superdense neutron star or sometimes a black hole.
So, in today's UCDs, a good part of their mass is made up of these dark remnants, largely invisible to Earth-based telescopes but fossils of a more dramatic past.
According to Dabringhausen, "Billions of years ago, UCDs must have been extraordinary. To have such a vast number of stars packed closely together is quite unlike anything we see today. An observer on a (hypothetical) planet inside a UCD would have seen a night sky as bright as day on Earth." (ANI)