Frontier Fields: Hubble Goes Deep
Astronomers use a clever way to look even farther with Hubble
Astronomers made a bold move in the mid-1990s, using the Hubble Space Telescope to stare at a seemingly vacant patch of sky.
Their efforts paid off. Looking deeper into space than ever before, Hubble uncovered 3,000 galaxies. The light from many of these galaxies had traveled for billions of years, meaning that Hubble sees them as they were billions of years ago. Looking deeper into space is also seeing farther back in time. The observations, called the Hubble Deep Field (HDF), gave astronomers a glimpse of galaxies in the early universe.
Astronomers, however, wanted more: more deep fields, more directions on the sky, and more distant galaxies that would help them understand how galaxies grow and change over time. They took advantage of the powerful cameras installed on Hubble during later servicing missions to gaze even deeper into space.
In 2004, Hubble's new Advanced Camera for Surveys (ACS) broke the record for the most distant visible-light view into space with the Hubble Ultra Deep Field (HUDF) observations. The telescope found a dazzling array of 10,000 faraway galaxies.
After installation of the Wide Field Camera 3 (WFC3) in 2009, astronomers looked at the HUDF region again. This time, however, they used the Wide Field Camera 3 to study the distant universe in infrared light. Because the universe is expanding, the light from the most distant galaxies gets stretched from visible to infrared wavelengths. These new infrared observations were able to uncover additional galaxies at even greater distances.
Using a trick of nature
Now Hubble has reached the limit of its infrared vision. To probe deeper at these wavelengths, astronomers will have to wait for the James Webb Space Telescope (JWST), an infrared observatory scheduled to launch in 2018. In the meantime, however, astronomers can use a trick of gravity to see just a bit farther.
A galaxy cluster
can act like a lens
The complex mathematics of Albert Einstein's relativity boils down to one basic idea: mass warps space. In addition, light that passes through this warped space will have its direction bent. Thus, the gravity of a massive cluster of galaxies can gather and magnify light, just like a glass lens does. Astronomers can use these "gravitational lenses" to see galaxies behind a galaxy cluster that would otherwise be too far away and too faint.
Hubble will use this "natural lens" to push to the edges of its capabilities in a project called the Frontier Fields. By taking deep-field observations centered on large galaxy clusters, astronomers can search for galaxies near the dawn of time. They hope to find the typical galaxies that eventually will turn into galaxies like our Milky Way. The galaxies found in previous deep-field surveys have been the brightest, most massive galaxies in the early universe. For a more complete picture of galaxy development, astronomers must study the average and smaller-mass galaxies, too. Many of these galaxies will be prime candidates for JWST to study in detail.
The frontiers of the universe
The first of the Frontier Fields observations:
Pandora's Cluster magnifies galaxies far beyond it
The Frontier Fields census will last three years and will observe six galaxy clusters. Hubble astronomers will use the visible-light capabilities of ACS and the infrared-light power of WFC3. NASA's other Great Observatories, the Spitzer Space Telescope, an infrared observatory, and the Chandra X-ray Observatory also will take part in this ambitious study. Astronomers will use both Hubble and Spitzer, for example, to obtain more accurate distances to the galaxies than they would get from just one telescope.
Besides hunting for some of the most distant galaxies ever seen, astronomers also want to build up the number and statistics of faraway galaxies found in Hubble's other deep fields. While observing each cluster, Hubble will simultaneously image a nearby patch of sky. These observations, called parallel fields, will be new deep fields that will greatly increase our sample of distant galaxies and provide new directions on the sky in which to cross-check previous results.
Site of a cluster and its parallel field:
Increasing the number of deep-field observations
The Frontier Fields project, therefore, consists of 12 fields, one of each of the six clusters and one of each parallel field. The first observations began in late 2013. A preliminary image of the first cluster, called Pandora's Cluster, along with an image of its accompanying parallel field, was unveiled in January 2014 at the American Astronomical Society meeting in Washington, D.C.
First look at distant galaxies
The Hubble image of Pandora's Cluster uses new WFC3 observations in infrared light combined with previously taken visible-light data. It represents the deepest-ever picture taken of a cluster of galaxies. The stunning view is peppered with some of the faintest and most distant galaxies ever detected. Some galaxies appear as they looked more than 12 billion years ago, not long after the birth of our universe in the big bang. The magnified galaxies can appear up to 20 times larger than they would normally be seen. The Hubble image of the nearby parallel field, taken in visible light with ACS, uncovers roughly 7,000 galaxies scattered across space and time.
These new images represent only one-twelfth of the data that the Frontier Fields will eventually provide. The telescope will return to these two fields in May 2014, but this time observing the galaxy cluster with ACS and the parallel field with WFC3. The combined deep image in visible and infrared light, the diversity of fields under study, and the immediate availability of the data to the entire astronomical community make this program one of the most important Hubble has ever undertaken. What new discoveries will Frontier Fields reveal? Stay tuned for updates.