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Hubble Approaches the Final Frontier: The Dawn of Galaxies
Publication Date: Fall 2004
This Hubble Ultra Deep Field (HUDF) image is the deepest optical view of the universe ever seen by humans. Several expert teams are conducting detailed analysis on the image. One of those teams includes ASU astronomer Rogier Windhorst. The team is led by Haojing Yan, a recent ASU graduate now doing post-doctoral work for the Spitzer Space Center at the California Institute of Technology.
The image is helping scientists identify what may turn out to be the earliest star-forming galaxies. Astronomers think that the collective ultraviolet light from those galaxies was likely responsible for “re-ionizing” the universe back when it was seven times smaller than it is today.
“This is the dawn of galaxy formation,” Windhorst says. “Before this, there were probably just star clusters and giant molecular clouds like the Orion nebula in our galaxy. There were big, massive stars, but probably nothing like the shape of ordinary or even tiny galaxies.”
The HUDF looks back to approximately the first 750 million years after the Big Bang. “Around this time there were finally enough stars to turn all the neutral hydrogen in the universe into ionized hydrogen,” Windhorst says.
During the past few decades, astronomers have amassed evidence that we live in a re-ionized or “refried universe.” Windhorst explains that this so-called re-ionization epoch was a critical watershed for the evolving universe. During that early time, cold hydrogen atoms drifting in space were pumped up with so much energy from the ultraviolet starlight that they were stripped of their electrons. As a result, the universe once again became transparent to light, like the sun burning off a morning fog.
NASA’s new 6.5 meter James Webb Space Telescope is planned for launch in 2011. It will allow astronomers to peer even further back in time to the epoch of first light.The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA). Physical Science: Space Science