Image of the Day: Terzan 5 -A Massive Milky Way Fossil

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It's not the name of a Japanese scifi movie…Scientists have spotted stellar fossils in the center of the Milky Way, globular clusters orbiting in the central bulge which seem to have come from somewhere else.  Like all fossils these are vital evidence of the evolutionary processes which led to everything we see today.


Terzan 5 is a massive blob of over a million tightly packed stars, with up to 10,000 per cubic light-year.  (Out with us it's less 0.02 over the same volume.) Examining their output with the wonderfully named Very Large Telescope (which combines four eight-meter apertures into a singe instrument effectively two hundred meters across) scientists have spotted distinct stellar signatures of both old and young stars.

This composition indicates that Terzan 5 evolved its stellar populations as a dwarf galaxy, and must once have been much larger than it is now.  As old stars explode in supernovae they spread newly created material huge distances across space – so subsequently formed stars begin with more of these distinctive elements.  But the blasts are so gigantic they would throw this starborne material right out of the current globular cluster – indicating Terzan 5 and others like it were once small galaxies in their own right. 

It seems the Milky Way's massive bulge (and others like it) accrete over time as dwarf galaxies erode and are eaten up by passers-by. 

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The Daily Galaxy via ESO

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