Stars packed million times more densely in early universe

February 14th, 2009 - 7:27 pm ICT by IANS  

London, Feb 14 (IANS) Stars in ultra compact dwarf (UCD) galaxies, discovered recently, may have been packed a million times more densely than in the solar neighbourhood, according to calculations made by a team of astronomers.

UCDs, discovered in 1999, are still enormous by our standards, about 60 light years across, yet they are less than 1,000th the size of our own galaxy, the Milky Way. A light year is about 10 million km.

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.

Until 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. Study co-authors doctoral student Joerg Dabringhausen, Pavel Kroupa, a professor and their colleague Holger Baumgardt, from the University of Bonn, present a different explanation.

The astronomers think that at one time, each UCD had an incredibly high density of stars, with perhaps one million in each cubic light year of space, compared with the one that we see in the 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, said a university release.

So in today’s UCDs, a good part of the mass is made up of these dark remnants, largely invisible to Earth-based telescopes but fossils of a more dramatic past.

These findings were published in Monthly Notices of the Royal Astronomical Society.

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