February 2012 -  Dark Energy

Image yourself standing on the rim of the Grand Canyon at Sunset. Below is an abyss of colorful rock formations and plateaus sprinkled with plant vegetation. As your gaze is drawn upward, an army of Stars appear and sprinkle the Sky. This must be the inspiration that drove Vincent Van Gogh to paint “Starry Nights over the Rhone”

Not being Van Gogh, my first thoughts were on the distance of these Stars from earth and how many Stars adorn Space? Thanks to our Space Telescopes and Observatories; Hubble, Chandra, Spitzer, Compton, Wilkinson Microwave Anisotropy Probe (WMAP) and their predecessors, plus the countless Earth Base Telescopes and Observatories, we now know the answers to these questions.

The farthest Star that we can detect is 26 Billion Light years away, and the closest is 4.2 Light years. One Light year (distance light travels over a year) is equal to about 6 trillion miles.

The diameter of our universe is about 52 Billion Light years across (26 Billion is just the radius). In that Space a 100 Billion Galaxies, with each galaxy comprised of about 100 Billion Stars, populate our Universe. Our Sun is just one Star among the billions and billions of Stars. More current data from the Hubble Space Telescope indicates we are underestimating the number of Stars and Galaxies.

 At this point you would think that all these Stars and Galaxies would be the major constituents of our universe. That’s not the case. 100 Billion Stars X 100 Billion Galaxies = .5% of the total content of our universe. The Earth, all other planets, People and all of life made from elements such as Iron,  Oxygen, carbon, Zinc (known as heavy elements) comprise only .03% of the content of our universe.

 About 70% of our Universe is empty Space or so we thought. It turns out that Space is not an empty vacuum but an Expanding Energy Force (See article “Runaway  Universe”) that is pushing the Stars and Galaxies away from each other. Does this mean that as Space gets larger, the Energy Force gets stronger? Maybe and  most likely! In the beginning at the moment of the Big Bang, this energy force caused expansion of Space known as Inflation. Gravity from all types of  Matter slowed down this expansion, but Space expanded to such a large size that this energy force was able to overcome Gravity and restarted the expansion acceleration of our Universe. This Expanding Energy Force has been named Dark Energy.

 Alex Filippenko, one of the scientists on the Dark Energy discovery team during a lecture at Fermi Lab stated that Astrophysicists know very little about this Energy Force and are not sure what will happen in the far future. At this time it seems that Stars and Galaxies will disappear into oblivion. But we need not to worry about that event at the moment, because it will be billions of years before the Sky starts to go dark.

 Our Universe is divided into 6 components. 
1) Dark Energy:                          70%
2) Dark Matter:                            25% 
3) Free Hydrogen and Helium:  4%
4) Stars:                                       0.5%
5) Neutrinos:                               0.3%
6) Heavy Elements:                   0.03%


The picture I painted was of Stars and Galaxies resting nicely in Space while the "Dark Energy" is pushing them apart. Again this is not the case! Our Galaxy the “Milky way” and the “Andromeda Galaxy” a Galaxy 2 million light years away, are hurling towards each other on a collision course. In our next Cosmology adventure, Dark Matter and Gravity will enter the story. 
 
    My Sources: Dan Hooper,        Fermi Lab & University of Chicago
                          Alex Flilippenko  University of California, Berkely