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.
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.