Spheres suspended
Let’s go back to the initial definition that we have given of a star. First of all let us stop and think: have we ever seen a gas take on a definite shape, such as a sphere, without beong enclosed in a container? The answer obviously is no, because gasses tend to spread and occupy all the available space. Then how can it be that the gasses of the stars are somehow confined and don’t dispel into space? The explanation can be found once again in gas behavior: when compressed, a gas warms becomes warmer. Stars have a hydrostatic equilibrium thanks to the balance between two equal forces pulling in opposite directions: gravity, that tends to make matter collapse inwards toward the center, and pressure caused by the expansion of the hot gas, pulling outwards Astronomers estimate that temperatures at the center of the sun reach 15 million degrees Celsius and that density is about a dozen times the one of lead. Nevertheless the center of the sun is still gaseous because gas at such high temperatures is in a particular state called plasma where electrons and nuclei, are no longer bound by their classical atomic structure so they generate clouds of free-floating electrically charged particles; in this state, matter is highly compressible thus remaining in a gaseous state.
This eternal clash between forces lasts throughout the star’s long life. Star longevity has been one of the main problems for astrophysics to solve in the past. Stars in fact appear eternal and immutable compared to our life time. Let’s take the sun for instance: because Earth cannot exist without its star , we know that the sun is at least as old as our Planet which is about 4,5 billion years old. And this is not all: terrestrial fossil discoveries let us know that during all this time, the sun has continued to shine more or less as it does nowadays. The age problem is strictly related to the production system of the energy released. In fact, this energy could come solely from gravity: as the sun contracts it heats up and becomes brighter. Estimates on the gravitational energy available to fuel the process prove, however, that the sun cannot survive beyond thirty million years. Therefore there must be an alternative energy source to fuel the longevity that we have observed.
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17 June 2014
Beacons in space
It is 1967, a young astrophysics student of the University of Cambridge...
23 February 2012
Neutrinos: speed record?
Apparently the sensational discovery made by CERN researchers...
-
28 January 2014
Gaia satellite scanning the sky
On December 19, 2013 the new satellite Gaia lifted off from the launching pad...
14 May 2014
Another Earth in the Universe
NASA’s Kepler Telescope, has discovered the first Earth-sized extrasolar planet...
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31 March 2014
A day on board the International Space Station
How astronauts spend their time in space?
17 July 2012
The importance of being Higgs
On 4 July 2012 the CERN Director General, Rolf Dieter Heuer...
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17 June 2014
Beacons in space
It is 1967, a young astrophysics student of the University of Cambridge...
-
23 February 2012
Neutrinos: speed record?
Apparently the sensational discovery made by CERN researchers...
-
28 January 2014
Gaia satellite scanning the sky
On December 19, 2013 the new satellite Gaia lifted off from the launching pad...
From the Multimedia section
Facts
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The comet’s tail
Comets are “dirty snowballs” that spend most of their life at the edges of the Solar System...
The definition of a dwarf planet
Astronomy, like all scientific disciplines, is continuously evolving...
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The cosmic microwave background radiation
In 1965, while studying the ground noise of a radio antenna...
Cosmic collision
When two galaxies start to approach, the tidal attraction forces deform their structures...
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The comet’s tail
Comets are “dirty snowballs” that spend most of their life at the edges of the Solar System...
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The definition of a dwarf planet
Astronomy, like all scientific disciplines, is continuously evolving...
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The comet’s tail
Comets are “dirty snowballs” that spend most of their life at the edges of the Solar System...
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The definition of a dwarf planet
Astronomy, like all scientific disciplines, is continuously evolving...