Astronomers have combined the largest and most comprehensive "history book" of galaxies into a single image using 16-year observations with NASA's Hubble Space Telescope.
The deep-sky mosaic of almost 7,500 individual images provides a broad portrait of the distant universe with 265,000 galaxies spanning 13.3 billion years to just 500 million years after the Big Bang. The weakest and farthest galaxies are only a ten-billionth of the brightness of what the human eye can see. The evolutionary history of the universe is also recorded in this one comprehensive view. The portrait shows how galaxies change over time and evolve into the giant galaxies observed in the nearby universe.
This ambitious undertaking, called Hubble Legacy Field, also combines observations of several Hubble deep field investigations, including the eXtreme Deep Field (XDF), the deepest view of the universe. The wavelength range extends from ultraviolet to near infrared light and captures the key features of galaxy assembly over time.
"Now that we have become broader than in previous investigations, we collect much more distant galaxies produced by Hubble in the largest such dataset that ever exists," said Garth Illingworth of the University of California at Santa Cruz, chief of the team that compiled the picture. "This one image contains the entire history of the growth of galaxies in the universe, from their time as 'infants' to their full grown & # 39; adults & # 39 ;."
No image will surpass this image until future space telescopes are launched. "We have assembled this mosaic as a tool for ourselves and other astronomers," Illingworth added. "The expectation is that this survey will lead in the coming years to an even more coherent, deeper and more comprehensive understanding of the evolution of the universe."
The picture provides a vast catalog of distant galaxies. "Such exquisite high-resolution measurements of the numerous galaxies in this catalog enable a wide range of extragalactic studies," said catalog research director Katherine Whitaker of the University of Connecticut in Storrs. "This type of investigation has often led to unexpected discoveries that have had the greatest impact on our understanding of galaxy evolution."
Galaxies are the "markers of space," as astronomer Edwin Hubble described them a century ago. Using galaxies, astronomers can track the expansion of the universe, give clues to the underlying physics of the cosmos, detect the formation of chemical elements, and determine the conditions that eventually led to the formation of our solar system and life.
The view contains about 30 times as many galaxies as in the previous depth fields. The new portrait, a mosaic of several snapshots, covers almost the entire width of the full moon. The XDF, which penetrated deeper into space than this other view, lies in this region, but covers less than one tenth of the full moon diameter. The Legacy Field also reveals a zoo with unusual objects. Many of them are the remnants of galactic "train wrecks", a time in the early universe when small, young galaxies collided and fused with other galaxies.
To put all observations together was an immense task. The picture includes the collective work of 31 Hubble programs of various astronomy teams. Hubble has spent more time in this tiny area than in any other sky region, more than 250 days in total, which is almost nine months.
"Our goal was to put together every 16 years of exposure to a legacy image," explained Dan Magee of the University of California at Santa Cruz, the team's data-processing supervisor. "Previously, most of these images were not compiled in a unified way that any researcher could use, and astronomers can select the data they want in the legacy field and work with it right away, rather than having to do a large amount of data reduction before performing it scientific analyzes. "
The image as well as the individual images that make up the new view are available to the worldwide astronomical community via the Mikulski Space Telescope Archive (MAST). MAST, an online astronomical database of Hubble and other NASA missions, is located at the Space Telescope Science Institute, Baltimore, Maryland's Far-Universe. After the launch of Hubble in 1990, astronomers discussed whether it would be worth spending part of the telescope's time on a "fishing expedition" to take a very long exposure of a small, seemingly empty piece of sky. The resulting Hubble Deep Field image from 1995 captures several thousand invisible galaxies in one point. The brave effort was a groundbreaking demonstration and definitive proof-of-concept, creating the conditions for future deep-field images. In 2002, Hubble's Advanced Camera for Surveys went deeper, revealing 10,000 galaxies in a single snapshot. Astronomers used exposures from the Hubble Wide Field Camera 3 (WFC3) installed in 2009 to compile the 2012 eXtreme Deep Field snapshot. Unlike previous Hubble cameras, the telescope's WFC3 covers a broader wavelength range from ultraviolet to near-infrared.  This new image mosaic is the first in a series of Hubble Legacy Field images. The team is working on a second set of images with more than 5,200 Hubble images in a different area of the sky. In the future, astronomers hope to extend the multi-wavelength range in the altar images to longer-wave infrared data and high-energy X-ray observations from two other major NASA observatories, the Spitzer Space Telescope and the Chandra X-ray Observatory.
] The large number of galaxies in the Legacy Field image is also a major target for future telescopes. "This will set the stage for NASA's proposed Wide Field Infrared Survey Telescope (WFIRST)," said Illingworth. "The Legacy Field is a forerunner of WFIRST, which takes a picture 100 times larger than a typical Hubble photo, and in just three weeks of WFIRST observation, astronomers can compose a field that is much deeper and deeper than double the size of Hubble Legacy Field. "
Astronomer helps to create a "history book" of the universe
Mikulski Space Telescope Archive (MAST): archive.stsci.edu/
HubbleSite Legacy Field image downloads: hubblesite.org/image/4492/news
Hubble Astronomers Gain Comprehensive Insights into the Emerging Universe (2019, May 16)
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