Unit 1:  Our place in the Universe                                          1   2   3   4  

1. The Universe: composition and structure

     Thanks to WMAP space probe we know that there are three different components

     in the Universe:

• Dark energy

                    It represents about 74 % of the matter-energy of the Universe.

        It is an unknown kind of energy responsible for the acceleration of the expansion

        of the Universe.

        Dark energy acts as a repulsive force against the gravity and for some scientists

        it is similar to the cosmological constant which Einstein had introduced

        in his equations, although today it acquires a different meaning.

                   Others scientists attribute it to energy fields of the vacuum that they call

        quintessence (the name that Aristotle gave to the fifth element which

        formed the skies)

• Visible matter

                    This is the matter which forms galaxies, stars, cosmic dust, etc. It is formed by:

                - 75% Hydrogen

                - 20 % Helium

                - 5% the rest of the chemical elements

         It is distributed in a heterogeneous way in the Universe.

         It is concentrated in determinate places while other remains empty of it.

                     The general structure of the Universe is formed by huge empty spaces

         (similar to bubbles) separated by filaments of matter (galaxies).

         These filaments present nodes, galaxy groups called galaxy superclusters

           within which there are other smaller groups called galaxy clusters.

                      Visible matter represents only around 4% of the total of the matter-energy of

         the Universe, so that it is possible that the empty regions do not be so empty.

         Astronomers suppose that they can be filled by other type of matter called

         dark matter.

• Dark matter

                    It represents the 22% left of the total of the matter-energy of the Universe. 

                   Its nature is still unknown because it does not emit or absorb electromagnetic

        energy (light, radio waves, etc) which allow us detect it and its existence only

        can be put in evidence indirectly through its gravitational effects over galaxies.

1.1. Answer these questions:

      a.   Where is dark matter located in this model of a supercluster of galaxies?

      b.   What effects does this dark matter have over the rest of the components of the Universe?

      c.   What role did the dark energy have in the development and evolution of the Universe?

      d.   What percentage of the whole Universe does visible matter represent?

           What is it made up of?

      e.   What is the cause of the irregular distribution of galaxies in the Universe?