StarDate:
Debbie Byrd
behavior. We'll tell you how -- after this.
March 6 The Birth of the Galaxies
The vast size of a galaxy is difficult to comprehend. Some, including
our own Milky Way, are hundreds of thousands of light-years across.
But it's even more mind-boggling to reflect on the countless billions
of galaxies in our universe.
Galaxies generally come in clusters. Clusters of galaxies group
together on the scale of the whole universe to create a spectacular
cosmic tapestry.
We can observe galaxies -- but no one is sure how they came to be.
Galaxy formation has always been a puzzle. But recently advances have
been made toward a solution to the puzzle. In one current model, the
universe started out with 90 per cent cold, dark, invisible matter and
l0 per cent ordinary matter. The cold, dark matter contained locations
of high density which may have acted as gravitational potholes to trap
ordinary matter. Ordinary matter -- heated in the potholes -- may have
evolved into galaxies.
The new model suggests that the potholes tended to move towards each
other and merge. Those formed early in the history of the universe
were shallow -- and their galaxies merged quickly into larger
structures. Later, deeper potholes formed which moved more slowly
towards each other. Developing galaxies therefore had more time to
cool and condense before collisions occurred. The result was not a
merger but a dense clustering of galaxies. This speculation may
explain why certain kinds of galaxies appear more often in dense
clusters and why other kinds are more likely to be found with fewer
neighbors nearby.
Script by Holly Clark.
(c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin