Local Large-Scale Structure
Local Large-Scale Structure
Goals: Explore the local structure of the Universe.
Before starting, turn on: galaxy, local, Tully
You will be using: clipbox, polysize commands
In the previous sections, we described the Local Group of galaxies and the groups of galaxies that surround the Local Group. Now you will explore the structure of the local Universe and see what lies beyond the surrounding galaxy groups.
Fly out of the local galaxies and turn on the Tully Galaxy Catalog (Tully). Tully's multicolored points now occupy the rest of your view. Look only at the nearest galaxies by setting a clip box for these data. Run the command
clipbox 0,0,0 30,30,30This will show only the galaxies within 30 megaparsecs, about 100 light-years. Now fly outside of this box so that you have a view of the entire data set. Brighten the galaxies if necessary.
The most dominant feature is the dense red cluster near the center. Fly to this galaxy cluster. This dense cluster is the “downtown” for our region of the Universe, the center of our local supercluster. This is the Virgo Cluster.
The Virgo Cluster
Sixteen of Messier's galaxies are members of the Virgo Cluster, but this is a mere fraction of Virgo's 2,000-plus galaxies. While it is about 50 million light-years away, the immense gravity of the cluster affects our Local Group galaxies and pulls other galaxies toward it.
Now turn off the points and labels and turn off the local data group. If you fly right into the cluster, you may notice the faint glow of a few bright galaxies. In fact, the Tully Catalog has images placed on each point that represents the type of galaxy it is. These images are given the proper size and orientation, and the luminosity of the points is accurate. If you wish to see these images more prominently, increase their polysize. Because their slum value is fixed according to the galaxy's size, you will have to use the polysize command to increase the size of the polygons. Choose polysize from the Slider Menu and adjust the slider to your liking.
Turn on the labels for the Tully data set. You may see labels like “M31,” which refer to the Messier Catalog, or “NGC 4429,” which refer to the New General Catalog. At the center of the Virgo Cluster is M87, a massive elliptical galaxy extending out more than half a million light-years. Its most peculiar feature is the long, knotty jet of material streaming out from its center.
Reduce the polysize back to normal (the Polysize Slider should be at its left-most setting) and turn the points back on. If you orbit the Milky Way with the Virgo Cluster in sight, you will notice a stream of light-blue galaxies extending up toward the Virgo Cluster. This is the Ursa Major filament that, in the 2-D sky, traces a path from the constellation Virgo up to Ursa Major.
The scientist who compiled these data sets into one consistent catalog, Brent Tully of the University of Hawaii, color-coded the galaxies according to a group membership. All galaxies belonging to dense clusters are red, while the galaxies in the Local Group and other nearby groups are green. Galaxies belonging to the Ursa Major Filament are light blue.
Many more clusters, filaments, and spurs are out there. Within this 100-light-year box are more than 6,800 galaxies. Let's look at the entire data set by typing
cb offremoving the clip box and revealing the remaining 20,000 or so galaxies. We discuss this larger view of the Universe in the next section.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott