четвртак, 23. август 2012.

An estimated 10,000 galaxies are revealed in humankind's deepest portrait of the visible universe ever. View a full size version of this image, or a slightly farther look with Hubble's infrared camera, in medium or large format.

How do astronomers know when they have looked too far into space? Maybe when they have run out
of galaxies to view.

That hasn't happened yet. There are still far reaches of space that have not been explored by even the most powerful telescopes, innumerable galaxies that have not been seen by human eyes.

But astronomers using NASA's Hubble Space Telescope are getting closer, with new images that reveal some of the farthest galaxies ever seen, from when the universe was just 400 million years old.

Called the Hubble Ultra Deep Field, the view represents the deepest portrait of the visible universe ever achieved by humankind. The snapshot 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.

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 until now were too faint to be seen by ground-based telescopes, or even in Hubble's previous faraway looks, called the Hubble Deep Fields, 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 Hubble Ultra Deep Field project lead. The combination of ACS and NICMOS images will be used to search for galaxies that existed between 400 and 800 million years (ranging from redshift 7 to 12) after the big bang. A key question for 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 Ultra Deep Field contains an estimated 10,000 galaxies. In ground-based photographs, 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 so empty that only about seven stars within the Milky Way galaxy can be seen in the image.

Photo credit: NASA/ESA/S. Beckwith(STScI) and The HUDF Team

and here is story 

The Big Bang Never Happened (1992) Lerner 


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