Chapter IV
Top / Bottom1/3 2/3SideOur Solar SystemStars and Galaxies.................................................................................................
Fig. 4.15 Our Solar System in the Milky WayFig. 4.16 Shape of the Milky WayImages taken recently through the Hubble space telescope show the different stages in
the birth process of stars. These pictures show that powerful energy, ultraviolet radiation
and high speed gas clouds unleashed by adult stars are triggering the birth of new stars
in the surroundings. Ultraviolet light emitted by the neighbor stars energizes the clouds.
Inside these huge interstellar gas columns, the density can become so high that gravity
takes over and causes the gas cloud to collapse and split into smaller clumps or gas eggs.
When compression continues a nuclear fusion will ignite their cores so that they become
fledgling stars.
The pressure and temperature in the cloud will rise to a point where nuclear reactions
arise. After this point is reached, the star will shine for millions of years. A star like the sun,
can live for over 10 billion years. Bigger stars are often burned out after 20 billion years.
Generally speaking, we can say that the younger stars have violet/blue colors, the middle
aged ones are yellowish, the older ones are red-brown and the oldest are black. As the
star ages it might turn into a white dwarf through a lack of fuel, or into a supernova
through explosion, or into a black hole through implosion. According to the estimated age
of many stars, it is clear that our Milky Way must be over 12 billion years old.