The Hubble Space Telescope's newest deep space image reveals 5,500 galaxies in a tiny patch of sky in the constellation Fornax.Not many pictures can take you through 13.2 billion years of history. The newest image released by the Hubble Space Telescope does just that. Astronomers compiled the eXtreme Deep Field from hundreds of Hubble Space Telescope images taken over the past decade, amounting to 2 million seconds of exposure time. The most distant galaxy in this image emitted its photons only 450 million years after the Big Bang.
Before the Hubble started snapping pictures of the distant universe, astronomers could only peer across 7 billion light-years, back to a time when the universe was half its current age. Hubble changed that in the late 1990s with the famous Hubble Deep Fields. Long exposures of a tiny, dark patch of sky in the Fornax constellation resolved thousands of galaxies, Hubble’s most powerful illustration of the vast expanse of the universe. The Ultra Deep Field, released in 2004, zoomed in for a narrower, deeper view of 10,000 galaxies.
Now the eXtreme Deep Field zooms in again, focusing on an area roughly half the size of the UDF and capturing 5,500 galaxies, some emitting photons just 450 million years after the Big Bang, in more detail than ever before. The eXtreme Deep Field incorporates observations taken over the past decade, including the Ultra Deep Field observations and many more. See how the Hubble team did it (scroll to the bottom of the page for the slideshow).
While the Ultra Deep Field was taken using four wavelengths of light, from visible to near-infrared wavelengths, the XDF does better. The eight wavelengths used to create the image extend all the way to 1.6 microns, a wavelength roughly twice the length of the reddest color the eye can see. To make galaxies glowing in the infrared visible in the image, the XDF team shifted the color scheme. Galaxies that would normally look yellow to human eyes appear blue in the image, explains Anton Koekemoer (Space Telescope Science Institute), who led production of the visible light portion of the Ultra Deep Field but was not involved in the current Hubble release.
Infrared imaging is crucial for finding the most distant galaxies, explains Garth Illingworth (University of California, Santa Cruz), principal investigator of the Hubble Ultra Deep Field 2009 program. The wavelength of light stretches as the universe expands, so as we look across the universe and back in time, the galaxies get redder and redder. First they’re no longer detected with blue filters, then they disappear from the redder filters. “At some point,” Illingworth says, “there is no light left to detect!”
As remarkable as the latest Hubble image is, it can only find galaxies living in a universe roughly 400 million years old. To see a younger universe, astronomers need images taken with “redder” infrared light. “We need the James Webb Space Telescope,” says Illingworth, referring to the controversial infrared telescope, currently under construction, that is expected to succeed the Hubble.
The Hubble eXtreme Deep Field Observing Team has invited the public to participate in a webinar at 1:00 p.m. EDT on Thursday, Sept. 27. Meet Garth Illingworth, Pascal Oesch, and Dan Magee (UC Santa Cruz), each members of the team that created the image you see above. Visit http://hubblesite.org/go/xdf/ to participate in the webinar.