Using its near-infrared vision to peer nine billion years back in time, NASA's Hubble Space Telescope has uncovered an extraordinary population of young dwarf galaxies brimming with star formation, the U.S. space agency announced on Thursday.
While dwarf galaxies represent the most common type of galaxy in the universe, the rapid star-birth observed in these newly- found examples may force astronomers to reassess their understanding of the ways in which galaxies form.
The galaxies are a hundred times less massive, on average, than the Milky Way, yet they churn out stars at such a furious pace that their stellar content would double in just 10 million years. By comparison, the Milky Way would take a thousand times longer to double its star population.
The universe is estimated to be 13.7 billion years old, and these newly-discovered galaxies are extreme even for the young universe -- when most galaxies were forming stars at higher rates than they are today. Astronomers using Hubble's instruments could spot the galaxies because the radiation from young, hot stars has caused the oxygen in the gas surrounding them to light up like a bright neon sign.
"The galaxies have been there all along, but up until recently astronomers have been able only to survey tiny patches of sky at the sensitivities necessary to detect them," said Arjen van der Wel of the Max Planck Institute for Astronomy in Germany, lead author of a paper on the results to be published online on Nov. 14 in The Astrophysical Journal. "We weren't looking specifically for these galaxies, but they stood out because of their unusual colors. "
The observations were part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), an ambitious three- year study to analyze the most distant galaxies in the universe. CANDELS is the first census of dwarf galaxies at such an early epoch.
"In addition to the images, Hubble has captured spectra that show us the oxygen in a handful of galaxies and confirmed their extreme star-forming nature," said co-author Amber Straughn at NASA's Goddard Space Flight Center. "Spectra are like fingerprints. They tell us the galaxies' chemical composition."
The CANDELS team uncovered the 69 young dwarf galaxies in near- infrared images taken with Hubble's Wide Field Camera 3 and Advanced Camera for Surveys.
The observations suggest that the newly-discovered galaxies were very common nine billion years ago. However, it is a mystery why the newly-found dwarf galaxies were making batches of stars at such a high rate.