Somewhere in the distant, old Universe, a population of stars hide undetected. They were the first to form after the birth of the Universe and are supposed to be far bigger in mass than any star visible today.
Astronomers know they must have been out there: only in this way could they solve the riddle of the origin and composition of stars in today’s Universe. A couple of ESA missions will help astronomers search for this elusive population.
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http://www.esa.int/export/esaCP/SEM99G1A6BD_Expanding_0.html