On September 25, 2012, Hubble released another “deepest image ever taken of the universe,” this one called the Hubble eXtreme Deep Field. This image shows more galaxies, fainter galaxies, and farther galaxies than any other image before it. Within the new deep field image are a handful of galaxies located about 13 billion light-years away. And, since the light from those galaxies has taken 13 billion years to cross the intervening space, we see these galaxies as they were less than a billion years after the beginning of the universe.
We can look out in space, and thus back in time, to see galaxies and the formation of galaxies just after the Big Bang. How’s that for a deep thought? Consider it as you watch this video showing the tiny 2D area and vast 3D extent of the Hubble eXtreme Deep Field:
CREDIT: NASA, ESA, and G. Bacon, F. Summers, and Z. Levay (STScI)
Astronomers call such long exposures “deep” because fainter objects tend to be farther away, hence, a longer exposure sees deeper into the universe. The new deep field is the latest in a line extending back to the original Hubble Deep Field (HDF), released in 1996. That breakthrough observation was followed by the HDF South (1998), the Great Observatories Origins Deep Survey (2003), the Hubble Ultra Deep Field (HUDF, 2004), and the HUDF09 (2009).
The Hubble eXtreme Deep Field builds upon the HUFD09 image by adding all Hubble observations that, done for a variety of research programs, cover the HUDF field on the sky. In that sense, it should perhaps be called the HUDF12, but that’s less catchy and trendy than calling it “extreme.”
However, calling it extreme does have its perils as well. It implies that Hubble will never exceed it, which is wrong. Observations continue to be taken and two programs in particular will add significantly to the data set. One will continue to add to the infrared portion of the image, as was the major improvements seen in the 2009 and 2012 deep field images. Another will flesh out the ultraviolet observations in a program one colleague jokingly referred to as “deep purple.” (Younger readers should look that up on Wikipedia while older readers immediately start humming the intro guitar riffs to “Smoke on the Water.”)
Will there ever be a “deepest” image? The answer can be both “no” and “yes.”
No, there will just be a series of “deepest yet” images, as astronomers will continually build new instruments and new telescopes enabling better observations. Deep fields with the James Webb Space Telescope are already eagerly awaited.
But also “yes,” if one thinks in terms of depth in space. As we look farther out in space and further back in time, we will get to a point before the first stars and galaxies formed. Earlier than about 100-200 million years after the Big Bang, there may be no light to see. We can, in the not-too-distant future, reach the edge of the observable universe.
Whoa. Now that’s deep.