Humanity's Eye on the Universe
NASA's Hubble Space Telescope is one of humanity's greatest achievements. Since it was launched into the orbit in 1990, the HST has changed the way we understand the Universe. Hubble has helped scientists determine a more accurate age of the Universe, confirmed the existence of black holes at the center of most galaxies, and discovered planets outside our solar system. It has also provided evidence that the Universe's expansion is in fact accelerating due to a mysterious repulsive force dubbed "dark energy" which makes up as much as 75% of the entire Universe.
This page is dedicated to the Hubble Deep Field: a set of incredible astronomical images revealing at least 1,500 galaxies visible in a tiny (1/28,000,000) and seemingly unremarkable patch of the sky within the Ursa Major constellation. You will find more information about how these photographs were taken, as well as the astonishing images themselves, below.
This page isn't meant to be a scientific reference, but rather a tribute to Hubble and a showcase of some of the most amazing pictures it helped produce. While the Deep Field program provided fundamental findings such as discovery of large numbers of galaxies distanced up to 12 billion light years away, it is only a part of the scientific discoveries made thanks to the Hubble.
Hubble Deep Field Images
The Hubble Deep Field (HDF) is an image of a tiny region of the sky in the constellation of Ursa Major. In area it is a mere 5.3 square arcminutes - approximately 1/28,000,000 of the total area of the sky, roughly the width of a dime held 75 feet away.
As many as 342 separate exposures were taken using the Hubble's WFPC2 (Wide Field and Planetary Camera 2) over 10 days between December 18th and 28th, 1995 in order to construct the Deep Field image. During this time the Hubble Space Telescope orbited the Earth 150 times.
That specific target area was carefully chosen by scientists for several reasons. First of all, it was inside Hubble's continuous viewing zones (CVZs): the areas of sky which are not occluded by our planet or the Moon during Hubble's orbit. More importantly, it had to avoid bright sources of visible light (as well as sources of infrared, ultraviolet and X-ray emissions) - such as known stars.
The field that fulfilled these criteria and was chosen to set the Hubble's sight on is thought to have less than twenty foreground stars from our galaxy, the Milky Way. That means almost all of the 3,000 lights in the image are galaxies, each with tens and hundreds of billions of stars of their own. And we saw all this in a tiny speck of sky even smaller than a 1x1 millimeter dot on a piece of paper held 1 meter away!
Gazing into this unremarkable patch of sky...
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Hubble had unveiled thousands of galaxies:
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It's quite humbling to realize that every one of those lights is a galaxy with tens or hundreds of billions of stars each. Our Sun is but one of a hundred billion stars in the Milky Way, which itself is but one of a hundred billion galaxies. "Tiny" does not seem adequate to describe how small we are in this vast and amazing Universe.
The completed Hubble Deep Field images were revealed at a American Astronomical Society meeting in in January 1996. Approximately 3,000 distinct galaxies of various shapes (elliptical, spiral and irregular ones) were identified by scientists, some of them being only a few pixels in width. The image also contains about 50 blue point-like objects that are thought to be either regions of intense star formation associated with nearby galaxies, or distant quasars. There's also a small possibility that some of these objects are old white dwarf stars.
Light from the galaxies in the HDF images took billions of years to reach Earth, meaning we now see them as they looked that far back in the past. One of the biggest findings of the Deep Field was a large number of galaxies distanced as far as 12 billion light years away; since the age of the Universe is thought to be between 13.5 and 14 billion years, those are young galaxies, having existed "only" 1.5 to 2 billion of years after the Big Bang. This provided cosmologists with a lot of rich material concerning the evolution of galaxies and the rate of star formation in the early Universe.
The Deep Field wasn't the end of Hubble's achievements though. NASA astronauts visited the Hubble for the fourth time in March 2002 aboard a space shuttle Columbia. Servicing Mission 3B installed a new optical Advanced Camera for Surveys (ACS), revived an unusable infrared camera that had previously ran out of coolant, and gave the space telescope new - smaller and more powerful - solar wings.
Thanks to these upgrades performed in orbit, Hubble became a much more powerful machine than it was on it's launch back in 1990. The ACS in particular increased HST's discovery efficiency by a factor of ten and quickly became the primary imaging instrument of the Hubble.
This allowed astronomers to see even farther into the depths of the Universe and produce the deepest, most sensitive astronomical image ever made at visible wavelengths: the Hubble Ultra Deep Field.
Hubble Ultra Deep Field: One Step Further
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The Hubble Ultra Deep Field too is an image of a very small section of space, equal to roughly one thirteen-millionth of the total area of the sky, or just one-tenth the diameter of the full moon as viewed from Earth. Indeed, NASA themselves compared HUDF to "peering through an eight-foot-long soda straw".
The target region is located in the southern hemisphere constellation Fornax, chosen like in HDF's case due to a low density of bright stars nearby (HUDF is thought to contain as little as 7 foreground stars).
The image was accumulated over a 4 month period from September 24, 2003 to January 16, 2004 (that's 400 orbits and over 800 exposures 21 minutes each!) Such a long observation was needed because photons of light from the very faint objects arrive at a trickle of one photon per minute, compared to millions of photons per minute from nearby galaxies. The Hubble Ultra Deep Field remains to this day the deepest portrait of the visible Universe ever achieved by humankind.
The Hubble Ultra Deep Field image is estimated to containas many as 10,000 galaxies. It looks back approximately 13 billion years in the past and is used to search for young galaxies that existed "merely" 400-800 million years after the Big Bang.
The high resolution HUDF image includes galaxies of different ages, sizes, shapes, and colors various distances away from Earth. Unlike current galaxies which usually assume elliptical or spiral shapes, these young ones are more chaotic: some look like toothpicks, links on a bracelet, or are merged together. The smallest and reddest galaxies of which there are around 100 in the picture are the most distant galaxies to ever have been imaged by an optical telescope, existing at the time "shortly" (~800 million years) after the Big Bang.
The HUDF build on the work of HDF and provided further material for cosmologists to analyze. The most important scientific results are:
- High rates of new star formation were observed during the very early stages of galaxy formation under a billion years after the Big Bang (that's how youngest galaxies were able to grow big in a relatively short time).
- The characterization of the distribution of galaxies, their numbers, sizes and luminosities throughout different epochs of the Universe was improved, providing insights into their birth and evolution.
- The HUDF confirmed that galaxies at high redshifts (farther from us) are smaller and less symmetrical than ones at lower redshifts (closer to us), clearly showing the rapid evolution of galaxies in the first couple of billion years after the Big Bang.
Spectacular Close-up on the Ultra Deep Field
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You can take a closer look at one area of the Hubble Ultra Deep Field in this galactic snapshot. A number of galaxies of various shapes and colors are visible. You can also see one bright foreground star from our own galaxy in this picture recognizable by it's distinct, cross-like appearance.
The Future of the Hubble Space Telescope
It is said that all journeys must come to an end. This phrase can be applied to Hubble's tireless work and the 19 year journey of orbiting the Earth as well: HST is expected to go out of commission sometime around 2020 (it's successor, the James Webb Space Telescope is due to be launched in 2018). Before that happens, however, Hubble will be used to look further into the Universe than ever before, this have been made possible because of the upgrades performed by one last maintenance mission - Servicing Mission 4 (SM4) - in May 2009.
During SM4 astronauts installed two new scientific instruments (Wide Field Camera 3 and the Cosmic Origins Spectrograph), repaired two instruments that have previously failed (the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph) and performed other replacements and improvements that should keep the Hubble Space Telescope functioning at least until the end of the decade.
The upgrades performed by the SM4 crew dramatically improved Hubble's capabilities to observe the Universe. Wide Field Camera 3 in particular has improved Hubble's discovery factor by 10 times. Thanks to the newest, cutting-edge technology upgrades it will be possible to look farther back in time and closer to the Big Bang than ever before.
Upgrades Performed by the Last Hubble Mission - Servicing Mission 4 (SM4) or Shuttle Mission STS-125.
May 2009 was the fifth and the last time humans visited Hubble. NASA scientists, engineers and astronauts worked hard to make Hubble better than ever before. See what they did during the mission aboard Space Shuttle Atlantis, from installing new science instruments to performing challenging repairs and numerous upgrades. Watch Hubble's Amazing Rescue if you want to learn more.