First galaxies had an explosive birth

Posted by Kate Taylor

New data from the South Pole Telescope indicates that the birth of the first massive galaxies in the universe happened a lot more suddenly than suspected.

Extremely bright, active galaxies were already fully-formed by the time the universe was 750 million years old, about 13 billion years ago.

The universe's first era of galaxy formation is known as the Epoch of Reionization. Most astronomers think that early stars came to life in massive gas clouds. The energetic light pumped out by these stars is thought to have ionized the hydrogen gas in and around the galaxies, creating huge 'ionization bubbles' that left a lasting signature in the cosmic background radiation (CMB).

"We find that the Epoch of Reionization lasted less than 500 million years and began when the universe was at least 250 million years old," says Oliver Zahn of the University of California, Berkeley.

"Before this measurement, scientists believed that reionization lasted 750 million years or longer, and had no evidence as to when reionization began."

The epoch's short duration suggests that monster galaxies with more than a billion stars played a key role in the reionization, since smaller galaxies would have formed much earlier.

The astronomers say they expect to learn a lot more about reionization from the South Pole Telescope. The current results are based on only the first third of the full telescope survey.There's also work underway to combine the telescope's maps with others made with data from the Herschel satellite, to provide more detiled information.

"We expect to measure the duration of reionization to less than 50 million years with the current survey," says post-doctoral fellow Christian Reichardt. "With planned upgrades to the instrument, we hope to improve this even further in the next five years."