Astronomers using the Hubble Space Telescope to survey the Ultra Deep Field have discovered a previously unseen number of galaxies from the dawn of the universe, looking further back in time than ever before and providing the deepest images of the cosmos ever produced.
The seven ancient galaxies discovered are believed to have formed over 13 billion years ago and are seen as they looked 350-600 million years after the theorized Big Bang. Their light is only now reaching Earth. The observations, led by Richard Ellis of the California Institute of Technology in Pasadena, were made using Hubble’s Wide Field Camera 3 (WFC 3) over a six-week period of time in August and September of this year.
The results of the survey, called UDF12, support the theory that galaxies gathered continuously over time. As Hubble peers further back in time and deeper into the universe, there is a noticeably steady decline in the number of galaxies that can be seen. The new data suggests that the “cosmic dawn,” the period when hydrogen clouds from the birth of our universe collapsed and became the first generation of stars and galaxies, occurred gradually over time—rather than being a single dramatic event.
“Our data confirms reionization was a gradual process, occurring over several hundred million years, with galaxies slowly building up their stars and chemical elements,” said Brant Robertson of the University of Arizona in Tucson.
Pushing Hubble to the absolute limits of its capabilities, the research is providing astronomers with the first reliable census of galaxies in the early universe. Hubble peered into one small patch of sky in the star constellation Fornax for over 100 hours, looking deeper into the universe in near-infrared light than any previous Hubble observation ever has. One of the seven newly discovered galaxies may actually be the furthest objects ever seen in the universe, observed an estimated 380 million years after the Big Bang—a time when the universe was only 3 percent of its present age.
“Our study has taken the subject forward in two ways,” Ellis explained. “First, we have used Hubble to make longer exposures. The added depth is essential to reliably probe the early period of cosmic history. Second, we have used Hubble’s available color filters very effectively to more precisely measure galaxy distances.”
“We added one filter, and undertook much deeper exposures in some filters than in earlier work, in order to convincingly reject the possibility that some of our galaxies might be foreground objects,” said team member James Dunlop of the Institute for Astronomy at the University of Edinburgh in Scotland.
The data provides new insights on the first generation of galaxies and stars to manifest in the early universe, at a time when the light from those stars cooked the gas in clouds surrounding them and made the universe transparent to light. The deaths of those first stars gave birth to heavier elements such as carbon and oxygen, and led to the formation of complex molecules which built the present universe—and life as we know it.
“This is an origins story, where we’re going back to the beginning, back to the first stars that appeared in the universe,” said NASA Associate Administrator for Science John Grunsfeld, who flew to space and serviced Hubble on three space shuttle missions (STS-103, STS-109, and STS-125). “These are baby pictures of the universe. This is the time when the universe was filled with hydrogen and starts to make stars and galaxies that make the chemical elements that we are primarily made out of—the oxygen we breathe, the iron in our blood, the calcium in our bones. Hubble is achieving just great science.”