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Galaxies: Snapshots in Time
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This sequence of NASA Hubble Space Telescope (HST) images of remote galaxies offers tantalizing initial clues to the evolution of galaxies in the universe.
[far left column]
These are traditional spiral and elliptical-shaped galaxies that make
up the two basic classes of island star cities that inhabit the
universe we see in our current epoch (14 billion years after the birth
of the universe in the Big Bang). Elliptical
galaxies contain older stars, while spirals have vigorous ongoing star
formation in their dusty, pancake-shaped disks. Our Milky Way
galaxy is a typical spiral, or disk-shaped galaxy, on the periphery of
the great Virgo cluster. Both galaxies in this column are a few tens of
millions of light-years away, and therefore represent our current stage
of the universe's evolution.
[center left column]
These galaxies existed in a rich cluster when the universe was
approximately two-thirds its present age. Elliptical galaxies (top) appear fully
evolved because they resemble today's descendants. By contrast, some spirals have a frothier
appearance, with loosely shaped
arms of young star formation. The spiral population appears more
disrupted due to a variety of possible dynamical effects that result
from dwelling in a dense cluster.
[center right column]
Distinctive spiral structure
appears more vague and disrupted in galaxies that existed when the
universe was nearly one-third its present age. These objects do not
have the symmetry of current day spirals and contain irregular lumps of
starburst activity. However, even this far
back toward the beginning of time, the
elliptical galaxy (top) is still clearly recognizable. However,
the distinction between ellipticals and spirals grows less certain with
increasing distance.
[far right column]
These extremely remote, primeval objects existed with the universe was
nearly one-tenth its current age. The distinction between spiral and
elliptical galaxies may well disappear at this early epoch.
However, the object in the top
frame has the light profile of a mature elliptical galaxy. This implies
that ellipticals formed remarkably early in the universe while spiral
galaxies took much longer to form.
Credit: A. Dressler (Carnegie Institutions of Washington), M. Dickinson (STScI), D. Macchetto (ESA/STScI), M. Giavalisco (STScI), and NASA
Image Type:
Astronomical
STScI-PRC1994-52c
This image includes the following images:
