Spheres that shine

To discover the system which is able to heat so much gas and for such a long time we have to dive into the microscopic world of atomic nuclei. Atoms have a precise structure: they have a nucleus formed by particles called protons and neutrons, around which orbits a cloud of smaller particles called electrons. We are in the extremely small world: take a millimeter, divide it by a million and then again by ten and we will have the size of an atom. Generally atoms are stable, but particular pressure, density and temperature conditions, can cause a reaction which will transform the atoms of a certain element into atoms of another element. Any alchemist’s dream!
The core of a star is a gigantic nuclear reactor where simple atoms melt and create more complex atoms. Most of a star’s existence is sustained by the fusion of hydrogen nuclei into helium nuclei. The energy produced by the reaction heats the gas which expands, thus opposing gravitational collapse, and then reaches the surface from where it scatters in space in the form of light and heat. Right at this very moment within the sun’s core 4 million tons of hydrogen are being burned per second; this impressing rhythm has remained the same for the past 5 billion years and will remain unchanged for the another 5.
When the main gas heating fuel runs out, the precious balance between forces that keep a star alive are lost. In the difficult search for a new stability, the star evolves, beginning fusion processes of heavier elements, such as carbon.
Then, from the core of a star like the sun, the enormous quantity of energy produced rises to the surface over millions of years. As it travels through thick layers of dense gas, this radiation interacts with gas atoms along the way and is degraded, somewhat like what happens to the kinetic energy in a billiard ball when it collides with another one. On its way, this energy will also pass through a turbulent gas layer where gas columns, rather like huge escalators, carry it up to the surface where it is released into space where it will travel until it reaches us.

Special reports

From the Multimedia section


  • 17 May 2011


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