Astronomy: Slow and steady

    Astrophys. J. 694, 1171–1199 (2009)

    Most nearby galaxies in the Universe are massive and filled with middle-aged stars, but how and when the galaxies formed is a topic of hot debate.

    To estimate galactic ages, Edward Taylor of Leiden University in the Netherlands and his colleagues studied 7,840 galaxies using the Multiwavelength Survey by Yale-Chile (MUSYC), which in total covers one square degree of the southern sky. They looked at the age of stars in galaxies as far away as 10 billion light years, and discerned that about one-fifth of large galaxies formed within the Universes first 4 billion years; 50% of the galaxies had formed by the time the Universe was 7 billion years old, about half its current age.

    The new survey data suggest that massive galaxies develop at a slower, steadier rate than previously believed.

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    Astronomy: Slow and steady. Nature 458, 682 (2009).

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