Hubble Goes Extremely Deep
Like photographers assembling a portfolio of their best shots,
astronomers have assembled a new, improved portrait of our deepest-ever view of
the Universe. Called the eXtreme Deep Field, or XDF, the photo was assembled by
combining ten years of NASA/ESA Hubble Space Telescope observations taken of a
patch of sky within the original Hubble Ultra Deep Field. The XDF is a small
fraction of the angular diameter of the full Moon.
The Hubble Ultra Deep Field is an image of a small area of
space in the constellation of Fornax (The Furnace), created using Hubble Space
Telescope data from 2003 and 2004. By collecting faint light over one million
seconds of observation, the resulting image revealed thousands of galaxies, both
nearby and very distant, making it the deepest image of the Universe ever taken
at that time.
The new full-color XDF image is even more sensitive than the
original Hubble Ultra Deep Field image, thanks to the additional observations,
and contains about 5,500 galaxies, even within its smaller field of view. The
faintest galaxies are one ten-billionth the brightness that the unaided human
eye can see.
Magnificent spiral galaxies similar in shape to the Milky Way
and its neighbor the Andromeda galaxy appear in this image, as do large, fuzzy
red galaxies in which the formation of new stars has ceased. These red galaxies
are the remnants of dramatic collisions between galaxies and are in their
declining years as the stars within them age.
Peppered across the field are tiny, faint, and yet more distant
galaxies that are like the seedlings from which today’s magnificent galaxies
grew. The history of galaxies — from soon after the first galaxies were born to
the great galaxies of today, like the Milky Way — is laid out in this one
remarkable image.
Hubble pointed at a tiny patch of southern sky in repeat visits
made over the past decade with a total exposure time of two million seconds.More
than 2000 images of the same field were taken with Hubble’s two primary cameras:
the Advanced Camera for Surveys and the Wide Field Camera 3, which extends
Hubble’s vision into near-infrared light. These were then combined to form the
XDF.
“The XDF is the deepest image of the sky ever obtained and
reveals the faintest and most distant galaxies ever seen. XDF allows us to
explore further back in time than ever before,” said Garth Illingworth of the
University of California at Santa Cruz, principal investigator of the Hubble
Ultra Deep Field 2009 (HUDF09) program.
The Universe is 13.7 billion years old, and the XDF reveals
galaxies that span back 13.2 billion years in time. Most of the galaxies in the
XDF are seen when they were young, small, and growing, often violently as they
collided and merged together. The early Universe was a time of dramatic birth
for galaxies containing brilliant blue stars far brighter than our Sun. The
light from those past events is just arriving at Earth now, and so the XDF is a
time tunnel into the distant past when the Universe was just a fraction of its
current age. The youngest galaxy found in the XDF existed just 450 million years
after the Universe’s birth in the Big Bang.
Before Hubble was launched in 1990, astronomers were able to
see galaxies up to about seven billion light-years away, half way back to the
Big Bang. Observations with telescopes on the ground were not able to establish
how galaxies formed and evolved in the early Universe. Hubble gave astronomers
their first view of the actual forms of galaxies when they were young. This
provided compelling, direct visual evidence that the Universe is truly changing
as it ages. Like watching individual frames of a motion picture, the Hubble deep
surveys reveal the emergence of structure in the infant Universe and the
subsequent dynamic stages of galaxy evolution.
The planned NASA/ESA/CSA James Webb Space Telescope (Webb
telescope) will be aimed at the XDF, and will study it with its infrared vision.
The Webb telescope will find even fainter galaxies that existed when the
Universe was just a few hundred million years old. Because of the expansion of
the Universe, light from the distant past is stretched into longer, infrared
wavelengths. The Webb telescope’s infrared vision is ideally suited to push the
XDF even deeper, into a time when the first stars and galaxies formed and filled
the early “dark ages” of the Universe with light.
Image: NASA, ESA, G. Illingworth,
D. Magee, and P. Oesch (University of California, Santa Cruz), R. Bouwens
(Leiden University), and the HUDF09 Team [high-resolution]
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