GALAXIES: SNAPSHOTS IN TIME



PHOTO RELEASE NO.:   STScI-PR94-52C                    



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

