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The Question

(Submitted December 22, 2010)

Mature elliptical galaxies have been spotted 1 billion years after the big bang. Considering that the stars within these type of galaxies should be at least 10 billion years old, and assuming that the same laws of physics apply to the early universe as apply to the present universe, why do these galaxies exist at all in the early universe.

The Answer

Indeed apparently fully assembled elliptical galaxies have been observed as early as 1 billion years after the Big Bang. The stars within these galaxies, however, are not as old as the stars in nearby elliptical galaxies. The best-estimate stellar ages are somewhat uncertain at the moment, but they are consistent with being formed after the Big Bang, so there are no problems here. This is quite interesting, since it has told us that galaxy assembly proceeds very rapidly after the big bang.

Bret & Antara
for Ask an Astrophysicist

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