Looking towards Creation

Categories: Cosmic Evolution

Called the Hubble Ultra Deep Field (HUDF), the million-second-long exposure reveals the first galaxies to emerge from the so-called "dark ages," the time shortly after the big bang when the first stars reheated the cold, dark universe. The new image should offer new insights into what types of objects reheated the universe long ago.

Hubble Ultra-Deep Field. Click image for full view
Image Credit: NASA/ESA/Hubble

The Hubble Ultra Deep Field (HUDF) image was produced by the Hubble Space Telescope, which has been orbiting Earth since 1990 as a joint project of NASA and the European Space Agency. Several hundred orbits of telescope time were allocated this winter to produce this new image, the deepest-ever of the universe, equivalent to an 11.5-day-long photographic exposure. The area of sky depicted in the HUDF is located in the constellation Fornax. Previous Hubble images have led to important discoveries about black holes, dark energy, the expansion of the universe, quasars, and gamma-ray bursts. However, none of the previous images have reached back so early into the beginnings of the universe, detecting light in this case from just 500 million years after the Big Bang.

With the public release of these impressive data, astrophysicists worldwide will scramble in the coming days to be the first to discover what the image, more dense with data than any previous Hubble image, reveals. This historic new view is actually two separate images taken by Hubble’s Advanced Camera for Surveys (ACS) and the Near Infrared Camera and Multi-object Spectrometer (NICMOS). Both images reveal galaxies that are too faint to be seen by ground-based telescopes, or even in Hubble’s previous faraway looks, called the Hubble Deep Fields (HDFs), taken in 1995 and 1998.

"Hubble takes us to within a stone’s throw of the big bang itself," says Massimo Stiavelli of the Space Telescope Science Institute in Baltimore, Md., and the HUDF project lead. The combination of ACS and NICMOS images will be used to search for galaxies that existed between 400 and 800 million years (corresponding to a redshift range of 7 to 12) after the big bang. A key question for HUDF astronomers is whether the universe appears to be the same at this very early time as it did when the cosmos was between 1 and 2 billion years old.

The Hubble Telescope looking towards Redshift 12 galaxies.
Credit: NASA

The HUDF field contains an estimated 10,000 galaxies. In ground-based images, the patch of sky in which the galaxies reside (just one-tenth the diameter of the full Moon) is largely empty. Located in the constellation Fornax, the region is below the constellation Orion.

The final ACS image, assembled by Anton Koekemoer of the Space Telescope Science Institute, is studded with a wide range of galaxies of various sizes, shapes, and colors. In vibrant contrast to the image’s rich harvest of classic spiral and elliptical galaxies, there is a zoo of oddball galaxies littering the field. Some look like toothpicks; others like links on a bracelet. A few appear to be interacting. Their strange shapes are a far cry from the majestic spiral and elliptical galaxies we see today. These oddball galaxies chronicle a period when the universe was more chaotic. Order and structure were just beginning to emerge.

The NICMOS reveals the farthest galaxies ever seen, because the expanding universe has stretched their light into the near-infrared portion of the spectrum. "The NICMOS provides important additional scientific content to cosmological studies in the HUDF," says Rodger Thompson of the University of Arizona and the NICMOS Principal Investigator. The ACS uncovered galaxies that existed 800 million years after the big bang (at a redshift of 7). But the NICMOS may have spotted galaxies that lived just 400 million years after the birth of the cosmos (at a redshift of 12). Thompson must confirm the NICMOS discovery with follow-up research.

This close-up of the large galaxy cluster Abell 2218 shows how this cluster acts as one of nature’s most powerful ‘gravitational telescopes’ and amplifies and stretches all galaxies lying behind the cluster core (seen as red, orange and blue arcs). Such natural gravitational ‘telescopes’ allow astronomers to see extremely distant and faint objects that could otherwise not be seen. A new galaxy (split into two ‘images’ marked with an ellipse and a circle) was detected in this image taken with the Advanced Camera for Surveys on board the NASA/ESA Hubble Space Telescope. The extremely faint galaxy is so far away that its visible light has been stretched into infrared wavelengths, making the observations particularly difficult.
Image Credit: NASA/ESA/Hubble

"The images will also help us prepare for the next step from NICMOS on the Hubble telescope to the James Webb Space Telescope (JWST)," Thompson explains. "The NICMOS images reach back to the distance and time that JWST is destined to explore at much greater sensitivity." In addition to distant galaxies, the longer infrared wavelengths are sensitive to galaxies that are intrinsically red, such as elliptical galaxies and galaxies that have red colors due to a high degree of dust absorption.

The Hubble Telescope.
Credit: NASA

This will hold the record as the deepest-ever view of the universe until ESA, together with NASA, launches the James Webb Space Telescope in 2011.Though ground-based telescopes have, to date, spied objects that existed just 500 million years after the big bang (at a redshift of 10), they need the help of a rare natural zoom lens in space, called a gravitational lens, to see them. Even much larger ground-based telescopes with adaptive optics cannot reproduce such a view. The picture required a series of exposures taken over the course of 400 Hubble orbits around Earth. This is such a big chunk of the telescope’s annual observing time–observations began Sept. 24, 2003 and continued through Jan. 16, 2004.

For each of the 10,000 galaxies that appear in what would look like empty space in the unaided view of the night sky, there are hundreds of billions of stars. By some estimates, the number of stars having planets may range between a quarter to half of those.

To put the number of stars in the visible universe in perspective, their total is estimated to be 70 sextillion, or 70,000,000,000,000,000,000,000 [seven followed by twenty-two zeros].

Such a vast population can be compared in a list of the very biggest numbers imaginable, with some terrestrial references borrowed from a combination of science and poetry:

  • ten times more than the number of grains of sand on Earth
  • eleven times the number of cups of water in all the Earth’s oceans
  • ten thousand times the number of wheat kernels that have ever been produced on Earth
  • one hundred million times more than the number of ants in all the world
  • one hundred million times the dollar value of all the market-priced assets in the world
  • ten billion times the number of cells in a human being
  • one hundred billion times the number of letters in the 14 million books in the Library of Congress

In the realm of astrobiology, it may be said that most meaningful terrestrial analogies to the number of stars in the known universe are indeed biological: only a fertile biosphere can yield such large numbers. One may ask how many living things the Earth itself can accomodate in its volume. If one cubic inch can hold ten billion animal or plant cells, and if one stacked these cells across both the land and oceans to a thickness of fifteen feet, the planet would be a vast teeming mass of biology–literally, life as far as the eye could see. The thickness of fifteen feet, while extreme overpopulation on the land, is likely an underestimate given the depth of the more three-dimensional ocean biosphere or the realms of winged species. In this way, the ceiling on the carrying capacity of Earth for cellular life is vast, since about ten million times the number of plant or animal cells could pack the planet than the number of stars in the visible universe. Compared to 70 sextillion, the cellular capacity terrestrially is estimated to be what can be called one undecillion, or ten raised to the power of 30.

The Space Telescope Science Institute (STScI) is operated by the Association of Universities for Research in Astronomy, Inc. (AURA), for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).