The Hubble Space Telescope continues to operate and provide breathtaking images of the cosmos even after almost three decades of faithful service. Its observations for NASA of distant galaxies, exoplanets, and the expansion of the universe have had a revolutionary impact on astronomy, astrophysics, and cosmology. What NASA has recently done with Hubble’s offerings is truly remarkable.
They have taken 16 years’ worth of observations and combined them all into one deep-sky mosaic image now known as the “Hubble Legacy Field“. Nearly 7,500 individual exposures went into the creation of the Hubble Legacy Field. This unbelievable mosaic they have constructed is being described as the largest and most comprehensive “history book” of galaxies.
All told, it contains roughly 265,000 galaxies that date back to just 500 million years after the Big Bang. The Hubble Legacy Field provides a wide portrait of the distant universe that looks back to the earliest visible times. The image even shows how galaxies have changed over time, growing through mergers to become the giant galaxies we see in the universe today. This effectively means that 13.3 billion years of cosmic evolution have been chronicled in this one image, hence why they are describing it as the history book of galaxies.
An impressive 31 Hubble programs and a range of different teams of astronomers, all collectively worked together to accomplish this ambitious endeavor. It also incorporated observations taken by several Hubble deep-field surveys. These include the Hubble Deep Field in 1995, the Great Observatories Origins Deep Survey (GOODS) of 2003, the Hubble Ultra Deep Field of 2004, and the eXtreme Deep Field (XDF) of 2012, which is the deepest view of the Universe to date.
Garth Illingworth, Professor Emeritus at UCSC and head of the team that assembled the image, said:
“Now that we have gone wider than in previous surveys, we are harvesting many more distant galaxies in the largest such dataset ever produced. No image will surpass this one until future space telescopes like James Webb are launched.”
Assembling this image was extremely difficult. Dan Magee, of the University of California, Santa Cruz, the team’s data processing lead, explained:
“Our goal was to assemble all 16 years of exposures into a legacy image. Previously, most of these exposures had not been put together in a consistent way that can be used by any researcher. Astronomers can select the data in the Legacy Field they want and work with it immediately, as opposed to having to perform a huge amount of data reduction before conducting scientific analysis.”
Modern Astronomy
What is so special about modern astronomy and cosmology is how key features of the galaxy assembly can be made apparent. The equipment is able to capture and reveal galaxies in the visible light, as well as the ultraviolet to the near-infrared part of the spectrum. The wavelength spans the entire range. For example, cosmic dust and gas are normally not always visible unless they illuminated by nearby stars.
Catalog lead researcher Katherine Whitaker of the University of Connecticut, in Storrs, said:
“Such exquisite high-resolution measurements of the numerous galaxies in this catalog enable a wide swath of extragalactic study. Often, these kinds of surveys have yielded unanticipated discoveries which have had the greatest impact on our understanding of galaxy evolution.”
This wider view contains about 30 times as many galaxies as the previous deep fields. The Legacy Field has also revealed several unusual objects. Many are the remnants of collisions and mergers that took place during the early Universe – what are referred to as galactic “train wrecks”. It is the most detailed and expansive image of galaxies ever taken.
More To Come
This new image is just the first in a series of Hubble Legacy Field images the teams are working on. The next set of images they will debut total more than 5,200 Hubble exposures, from another area of the sky. Looking ahead, astronomers hope to broaden the multiwavelength range in the legacy images to include even more data on galaxies. This will include longer-wavelength IR and high-energy X-ray observations from two other NASA Great Observatories – the Spitzer Space Telescope and the Chandra X-ray Observatory.
Team member Rychard Bouwens of Leiden University in the Netherlands said in ESA press release:
“One exciting aspect of these new images is the large number of sensitive color channels now available to view distant galaxies, especially in the ultraviolet part of the spectrum. With images at so many frequencies, we can dissect the light from galaxies into the contributions from old and young stars, as well as active galactic nuclei.”
For now, no image of the Universe is expected to surpass the Hubble Legacy Field images one until next-generation space telescopes are launched. These include the James Webb Space Telescope (JWST) and the Wide-Field Infrared Space Telescope (WFIRST), both of which will enable more in-depth surveys with improved resolution and sensitivity over Hubble.
The Legacy Field image is intended to be used as a map of the vast number of galaxies. It should be very helpful for astronomers to pick out galaxies to study with future telescopes. Illingworth said in a HubbleSite press release:
“We’ve put together this mosaic as a tool to be used by us and by other astronomers. The expectation is that this survey will lead to an even more coherent, in-depth and greater understanding of the universe’s evolution in the coming years… This will really set the stage for NASA’s planned Wide-Field Infrared Survey Telescope (WFIRST). The Legacy Field is a pathfinder for WFIRST, which will capture an image that is 100 times larger than a typical Hubble photo. In just three weeks’ worth of observations by WFIRST, astronomers will be able to assemble a field that is much deeper and more than twice as large as the Hubble Legacy Field.”
The videos below show the Hubble Legacy Field, but you can download the full image with its 20,791 x 19,201-pixel resolution here.
