Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard
Deborah & William Hillyard

Science - Large Scale Structure of the Universe


 
This section looks at Superclusters of galaxies.  This involves scales up to gigaparsec; that is, billions of light years.  As discussed in the previous section, our Galaxy, the Milky Way, is in the Local Group of galaxies.  In turn, this group is a part of the Virgo Supercluster that comprises more than 100 groupings and clusters of galaxies, of which the Virgo and Canes Venatici Clusters are the largest.  It is about 33 megaparsecs across.  Here is a movie "Flight to the Virgo Cluster" which is well worth a look; visually stunning. 

Superclusters

The Lynx Arc Supercluster

The Lynx Arc Supercluster is the furthest from us found to date, and is about 3.7 Gpc away.  Thus we are seeing it as it was when the Universe was only about 2 billion years old, while it is thought to be around 13.7 billion years old now.  Here is an artists impression of the Lynx Arc.  It is behind the Lynx Cluster of galaxies, which is around 1.7 Gpc away, though not in any way connected to it as it is much further away.  They are both named after the constellation, the Lynx, in which they are seen.  You can see the Lynx Arc in this picture (right; click to enlarge) of the Lynx Cluster as a smeared red streak that I have arrowed.  In fact we see it gravitationally lensed by an intermediate cluster of galaxies which is why it appears as a streak. 
The Perseus-Pisces Supercluster

The Perseus-Pisces is a very large supercluster; nearly 100 Mpc long.  It includes several very large clusters, including the huge Perseus cluster, the Pisces cluster and the Pegasus cluster.  It also borders the large Taurus void which is over 30 Mpc across.  Perseus-Pisces is part of the Perseus-Pegasus Filament; see the next section on Filaments & Walls. 
Superclusters are large groups of smaller galaxy groups and clusters, as well as isolated galaxies.  They are very large structures spanning between 20 and 100 Mpc or more in their long dimension.  They were once though to be the largest structures in the Universe, but are now seen as components of truly vast walls and filaments.  Astronomers believe that there are some 10 million superclusters in the observable
Universe.  Shown in the image to the right are some of the voids, virtually bereft of galaxies, that exist among the superclusters, generally bordered by filaments.  Here is a description of the larger scale clustering of galaxies.  This reference is brief, but contains a number of additional, useful sites that discuss the grouping of galaxies. 

Here is some information about a few of the significant Superclusters that have been identified:
The image to the right shows known super-clusters out to a 500 million light-year radius from our local super-cluster, Virgo.  
Astronomers have known since the 1980s that the Milky Way, and the Local Group, is moving towards Centaurus at a speed of between 150 and 300 miles/second relative to the Cosmic Microwave Background.  They called this anomaly the Great Attractor.  The direction in which it lies is close to the zone of avoidance in the Milky Way, so it is obscured by dust.  Initially, it became associated with the Norma Cluster, and was believed to be a concentration of mass, equivalent to tens of thousands of our Milky Way galaxy, approximately 75 Mpc away.  On the scale of the Universe, this is close by.  It was thought to affect the motions of galaxies, clusters, and super clusters over a range of many hundreds of millions of light-years.  In fact, recent observations have shown that the Great Attractor has only about one tenth of the mass it was thought to have.  Calculations showed that the Great Attractor region would account for less than half of the observed motion, and that part of this anomalous motion is due to the Shapley Supercluster that lies behind it.  In addition, it is possible that there is an even larger concentration of mass beyond the Shapley Concentration that has not been discovered.  Of course, as gravity falls off as the square of distance from us, if a mass were twice as far away as the Shapley Supercluster it would have to be four times the mass to exert the same gravitational attraction. 
The Great Attractor
Shapley Supercluster

Also Known as the Shapley Concentration, it lies approximately 200 Mpc away in the direction of Centaurus, and contains at least 25 clusters of galaxies, and has the mass of approximately 10,000 Milky Way galaxies, concentraded in a volume of space comparable to our own Virgo Supercluster.  It is the largest known concentration of matter in the nearby Universe.  To produce the observed motion of the Local Group, the mass needed at the Shapley distance is ~ 2.8 x 1017 solar masses.  The highest estimate for the mass of the Shapley that I have found is 1.3 x 1016 solar masses.  This would provide only about 5% of the gravitational force necessary; much less than is provided by the Great Attractor.  Abell 3558, also known as Shapley 8, is the largest cluster in the Shapley Concentration.  It is so large, that it seems itself to comprise a number of distinct groups of galaxies.  There are two other particularly large clusters.  Many astronomers believe that we have yet to see the full scale of the Shapley, and it may turn out to be much larger than it seems. 
A map showing the location of the Shapley Concentration with respect to the Milky Way galaxy. 
The Lynx Arc contains around one million extremely hot, young, blue stars, and is about one million times brighter than the Orion Nebula.  The light we see is predominantly ultraviolet light from these hot stars that has been red-shifted after travelling 12 billion light-years to reach us.  This level of intensity of ultra-violet could come only from stars that are very large and hot, with surface temperatures around 80,000º K.  This is about twice the temperature of the hottest stars that form today, and is due to the star comprising hydrogen and helium with the density of heavier elements being only about 5% the value for the Sun.  Of course this means that with masses several hundred times that of the Sun, they burn much hotter and last for a much shorter life span; possibly one or two million years compared to a star like the Sun that has a lifespan of around 10 billion years. 
Select: