Red star

 In four hundred billion of years the sun will become a Red Giant
and it will eat all the planetas of the solar system of the Milky Way.

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IS INTERESTING TO KNOW THAT  WE ARE "STAR DUST"

WHAT ARE THE INGREDIENTS OF THE COSMIC RECIPE?

People have always known that stars and any other of our cosmic neighbors  are very far away. So far, that in the XIXth century August Comte, a prominent philosopher, argued:

Of all objects, the planets are those which appear to us under the least varied aspect. We see how we may determine their forms, their distances, their bulk, and their motions, but we can never known anything of their chemical or mineralogical structure; and, much less, that of organized beings living on their surface ... (The Positive Philosophy, Book II, Chapter 1, 1842)

However, just a few decades later, astronomers started to identify elements in the solar atmosphere. And nowadays we have a good idea about the chemical makeup not only of the stars, but of the entire visible universe.

According to spiff.rit.edu, the Earth, the easiest celestial body to measure, is made up of the following elements:

• the atmosphere
• 78% nitrogen
• 21% oxygen
• 1% other stuff (carbon dioxide, water vapor, argon, etc.)
• the oceans
• water: 2 hydrogen, 1 oxygen
• the solid crust
• 62% oxygen (by number of atoms)
• 22% silicon
• 6.5% aluminum
• bits of iron, calcium, potassium, sodium
• a central core
• mainly iron
• smaller amounts of nickel and cobalt
• an intermediate mantle
• mostly oxygen and silicon
• some iron, magnesium, etc.

 

The composition of stars is largely different, comprising:

• 90% hydrogen (by number of atoms)
• 10% helium
• tiny traces of heavy elements (everything else)

Our galaxy contains not only stars, but also clouds of gas and dust. Some glow brightly, lit up by nearby stars. Other clouds appear dark, because they absorb and scatter the light which tries to pass through them. It is often easier to determine the composition of nebulae than of stars, since we can see into the center of the nebula. The spectra of these objects show that they, too, are almost completely made of hydrogen and helium, with tiny amount of other elements.

 

The blog spiff.rit.edu posts three important questions:

• Is there any particular reason that galaxies should have started out with a mixture of 12.5 hydrogen atoms for every 1 helium atom?
• Is there any reason why the initial mixture should contain only hydrogen and helium, with (almost) no heavier elements?
• Whence came the mixture of oxygen, silicon, iron, etc., which make up the Earth and everything on it?

 

Reference:

http://spiff.rit.edu/classes/phys240/lectures/elements/elements.html

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