Astronomie si cosmologie

[Enthroll]

HubbleSite - NewsCenter - Hubble Pans Across Heavens to Harvest 50,000 Evolving Galaxies (03/06/2007) - Release Images

A narrow slice of sky near the Big Dipper yielded a goldmine of at least 50,000 galaxies, which were spied by NASA's Hubble Space Telescope. The Hubble view is yielding new clues about the universe's youth, from its "pre-teen" years to young adulthood.

The image at left, taken by Akira Fujii with a backyard telescope, shows the location of the Hubble observations near the Big Dipper. The long, narrow image in the center is Hubble's panoramic view of the area, made by assembling 500 photographs taken over a one-year period. The 50,000 galaxies spied in the image are scattered across a region that is equivalent to the apparent diameter of two full Moons. The dimensions of the final mosaic are 21 images long by 3 images tall.

The image at right is a section of the panoramic photo.

A wide diversity of galaxies can be seen throughout both Hubble images. Some are beautiful spirals or massive elliptical galaxies like those seen in the nearby universe, but others look like random assemblages of material, the leftovers from violent mergers of young galaxies. These resemble some of the most distant, youngest galaxies observed.

The Hubble observation, made with the Advanced Camera for Surveys, is part of the All-wavelength Extended Groth Strip International Survey, a collaborative effort using major ground-based and space-based telescopes to focus on a narrow swath of sky near the Big Dipper. The region offers a clear view of the distant universe.

Astronomers studying the Groth Strip find that star formation is largely driven by the supply of raw materials, such as gas and dust, collapsing under the force of gravity. More massive galaxies form stars early, whereas the smaller galaxies create their stars over longer timescales. Both normal-looking, undisturbed galaxies and those showing signs of catastrophic collisions were forming an abundance of stars 8 billion years ago. This evidence suggests that violent galaxy mergers were not required for rapid star formation.