Tully's Nearby Galaxies
Tully's Nearby Galaxies
Goals: Discuss the structure of the nearby Universe.
Before starting, turn on: galaxy, local, Tully
You will be using: see command
Beyond those local features like the Virgo Cluster and the Ursa Major Filament, the Tully galaxies reveal the grand structure of the nearby Universe. Fly to the outer edge of the data and orbit. From this view, you will see the major structural elements: clusters, filaments, and voids.
Before we begin, let's first discuss the shape of these data. If you are orbiting far enough away, you will notice that the data appear to form a cube. In fact, they are confined to a cube. This is an artificial boundary that samples data within about 150 million light-years of the Milky Way.
Following from the previous tutorial, the colors are randomly assigned to a structural element, except for red, which is assigned to dense clusters. Within this cube are about 30,000 galaxies that cover a range of 300 million light-years. The Milky Way lies at the center of this observed data set.
Dense Clusters
As with many phenomena in nature, it is common to find galaxies in clusters. Some are small, loose agglomerations of galaxies, while others are massive, dense clusters of thousands of galaxies. Let's examine the dense clusters by typing
see abellat the Command Line. Now you should see the green points, which represent the local galaxies, and the dense, red clusters of galaxies surrounding us. Virgo is the closest, at about 50 million light-years, but many more are present in this data set. Often these clusters do not have an accurate number of galaxies within them. The see command tells us that there are about 1,700 galaxies showing; however, we know the Virgo Cluster alone has more than 2,000 galaxies.
Filaments and Voids
The other structures one sees in the nearby Universe are the filaments and voids. Filaments are strings of galaxies that often connect larger clusters. We discussed the Ursa Major Filament in the previous tutorial, and now we see that Virgo and the Ursa Major Filament are part of a large network of clusters and connecting filaments.
Follow the Ursa Major Filament up to the Virgo Cluster and beyond, up to another red cluster of galaxies. This is Abell 3526, located in the constellation Centaurus in our 2-D sky. Looser than Virgo, it seems to have a yellow line of galaxies extend over to it. These lead to the Antlia Cluster, at which point the yellow galaxies seem to take a right turn, where the filament connects up to another group of galaxies.
The yellow strands of galaxies define an edge, inside of which you see few galaxies until the aqua strand that seems to connect with the Virgo Cluster on the opposite side of Ursa Major. That large area where few galaxies are found is like the inside of a bubble. These regions of few large galaxies are called voids. The overall density of these regions is low relative to that of the galaxy-rich filaments. However, there are likely small dwarf galaxies that we cannot see in these regions.
The local Universe seems resemble a bubblelike form, where filaments of galaxies reside on the bubble surface and vast voids exist between them. These filaments connect large clusters of galaxies and make larger superclusters.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott