A team of scientists announced Wednesday that NASA’s Hubble Space Telescope has produced a comprehensive snapshot of the “cosmic dawn” of the universe, capturing a set of seven primitive galaxies that formed several hundred million years after the big bang.
“The situation is similar to having the first ultrasound of an infant,” said Avi Loeb, chairman of the astronomy department at Harvard University who praised the new data, saying it heralds the beginning of a transformation for a field that has thus far been largely theoretical. “These early galaxies represent the building blocks of the present-day galaxies that we have.”
The oldest galaxy of the set came very early in the lifetime of the universe, which began 13.7 billion years ago. That galaxy, scientists believe, dates to 380 million years after the rapid expansion of the universe known as the big bang. The other six galaxies date from 400 million to 600 million years after the big bang, and scientists noted that these offer glimpses of the universe when it was less than 3 percent of its current age.
“These images are giving us the tantalizing view of what happened in those very early stages of the universe,” said John Grunsfeld, an associate administrator at NASA and a former astronaut who in 2009 serviced Hubble, helping make possible recent observations. “This is the time when the universe, filled with hydrogen, started to make stars and galaxies that make the chemical elements we are literally made out of. The oxygen that we breathe. The iron in our blood. The calcium in our bones. This is the beginning of everything.”
Scientists emphasized that this discovery is important because it provides a “census” of primitive galaxies. That complete portrait will be important as scientists work not just to find the oldest objects in the universe, but also to unravel what happened during a pivotal point of development.
“We are actually counting a reasonable sample of galaxies. Of course, the most distant object is interesting, but it’s the census, the seven objects that give us the first indication of the population of objects,” said Richard Ellis, an astrophysicist at the California Institute of Technology who led the work, which will result in seven published papers.
He added that there was gradual galaxy growth and that “cosmic dawn was probably not a single dramatic event.”
One of the biggest questions that the new data will help scientists begin to answer is the question of what happened during a period of “reionization” when the universe reheated, prior to the formation of the first modern galaxies. During that time, hydrogen atoms split back into their components, protons and electrons. The primitive galaxies spotted by Hubble are from that time of intense interest.
“We don’t know the details exactly during that time,” Loeb said. “So one way of unraveling what really happened is to look at galaxies, like we are doing in this particular context.”