For years astronomers have believed the early universe was filled with young protogalaxies busily forming stars. Now, however, it appears the universe was composed of a wide variety of galaxies.
Astronomers from the Observatories of the Carnegie Institute of Washington (OCIW) in Pasadena, California, and the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, found the early universe — when it was 2 to 3 billion years old — had “dead” galaxies as well as young, active galaxies.
The scientists used the Infrared Array Camera (IRAC) on the Spitzer Space Telescope to look at a southern region of the Hubble Deep Field. There they found old, red galaxies that were no longer forming stars.
This discovery implies galaxies must have formed earlier than previously thought, if they could go through the entire cycle of star formation before the universe was 3 billion years old.
The astronomers also found the early universe was a more complex place than originally expected, with many different types of galaxies. According to Ivo Labbè, co-author of the study that will appear in an upcoming issue of The Astrophysical Journal Letters, “Overall, we’re seeing young galaxies with lots of dust, young galaxies with no dust, old galaxies with lots of dust, and old galaxies with no dust. There’s as much variety in the early universe as we see around us today.”
“We’re detecting galaxies we never expected to find, having a wide range of properties we never expected to see, ” said Jiasheng Huang of CfA, a co-author of the study.
Studies using infrared detection can probe further back in time than visible light, enabling astronomers to piece together the formation processes of the structures in our universe.