All the stars that we have talked about do not lie alone, lost
in the middle of the universe.
They are grouped together, by billions, in structures that are called galaxies.
These galaxies are exceedingly numerous. During the last inventory with the Hubble Space Telescope, it was calculated that the telescope was able to see about 80 billion galaxies. So, their number is estimated to be at least 150 billion in the visible universe.
Galaxies can take a lot of shapes, very smooth or very irregular, with two, four or six arms. However far you look in the universe, you will find galaxies.
We will make a journey among all these galaxies, very young and
energetic ones, or older galaxies which shine peacefully in the sky.
Above all, we will try to understand how these large structures evolve with time. A very turbulent evolution, but slow compared to our time scale.
More than the stars, the images revealed by the big telescopes will let us discover real wonders out to the fringes of our universe...
You could almost hear the stars
Twinkling up in the sky,
And the old wind woke and moaned in the spars
And the same old waves went by ...
Alfred Noyes (1880-1958)