Billions of years ago, when the universe was still in its infancy, the formation of stars is believed to have occurred at a much faster rate than it does today. Now, a recent discovery by NASA's Hubble Space Telescope (HST) suggests that the universe's earliest galaxies may have been pumping out stars even faster than we thought.
The picture up top was captured by the HST during a three-year scan of the universe known formally as the Cosmic Assembly Deep Extragalactic Legacy Survey — or "CANDELS" for short. The survey was undertaken to search for and analyze some of the most distant galaxies in the universe. This particular image highlights a collection of 18 dwarf galaxies as they existed some 9 billion years ago – that's fewer than 5 billion years into the universe's estimated 13.7-billion-year existence.
5-billion years may sound like a long time, but on a cosmological time scale, astronomers actually regard these galaxies as belonging to a relatively young universe, back when star formation is believed to have occurred considerably faster than it does today.
But according to Harry Ferguson — co-leader of the CANDELS survey — these tiny dwarf galaxies (the combined mass of the 18 shown up top doesn't add up to even one fifth the total mass of our own Milky Way) have been observed pumping out stars at a furious rate, even by early-universe standards.
By observing the radiation emitted from their newborn stars, Ferguson and his colleagues have concluded that these galaxies were churning out stellar bodies fast enough to double their total number of stars in just 10 million years. By comparison, the researchers estimate it would take the Milky Way 10 billion years to achieve a similar doubling. (The video featured here zooms in on Hubble imagery to reveal the young galaxies that are brimming with starbirth).
According to Ferguson, who is also a co-author of the paper describing the team's results, the latest HST observations actually come up against detailed studies of similarly-sized dwarf galaxies in orbit around the Milky Way.
"Those studies suggest that star formation was a relatively slow process, stretching out over billions of years," explained Ferguson.
"The CANDELS finding that there were galaxies of roughly the same size, forming stars at very rapid rates at early times, is forcing us to re-examine what we thought we knew about dwarf galaxy evolution."
Ferguson says that the team's findings could indicate that the proximity of a dwarf galaxy to a larger, spiral galaxy has an effect on its rate of star formation, but notes that at this point, ideas like these are just speculation. To get a better understanding of what's going on, he says we'll need technologies like the James Webb Space Telescope –- NASA's high-tech, infrared follow-up to Hubble.
"With Webb, we'll probably see even more of these galaxies, perhaps even pristine galaxies that are experiencing their first episode of star formation," said Ferguson. "Being able to probe down to dwarf galaxies in the early universe will help us understand the formation of the first stars and galaxies."