Much as a teacher would be amazed to enter a preschool classroom full of college-age students, astronomers were thrown for a loop when they found fully formed galaxies in a distant corner of the universe they thought was populated with relatively small, ragged gatherings of stars. The discovery, reported in July by Karl Glazebrook of Johns Hopkins University, calls into question the prevailing theory about when and how the Milky Way and other galaxies began to take shape.
That theory holds that it took many billions of years for small groups of stars to coalesce and evolve into massive, mature galaxies. Testing the model has been tough because groupings of stars at distances of 8 billion to 11 billion light-years away from us are so faint that they tend to vanish into the background glow of Earth’s atmosphere.
Using the giant Gemini North telescope atop Mauna Kea in Hawaii and an innovative sky-glow-subtraction technique, Glazebrook’s team analyzed spectra from 300 galaxies. “It’s the first comprehensive survey of all types of galaxies going back to 3 billion years after the Big Bang,” Glazebrook says. The results gave him pause. He did not expect to find any massive galaxies earlier than about 9 billion years ago because theoretical models predict that such large objects form last. In fact, massive galaxies not only showed up in the survey but “many of the stars we see in the galaxies at this epoch are already ‘old,’ meaning they formed much earlier,” he says.
Evidently, something big is awry concerning long-held assumptions about galactic evolution. A new model is needed to explain how large groupings of stars could have lit up and gathered together much more quickly than current cosmological models predict, Glazebrook says. “We really do not understand how massive galaxies turn their gas into stars. We need to find ways to account for this happening.”