Saturday, February 18, 2012

Ignite the Sun!

Butane lighters use friction to get the spark for ignition

Ignite the fire!
 Angi, fire, is a chemical reaction that often involves reaction with oxygen O2. School teachers cleverly show the importance of air by asking students to cover a burning candle with a glass. Before this educational experiment can go ahead the candle must somehow start burning - a matchstick or cigarette lighter will do. (Note the use of the English word "light" as a verb meaning "to bring light" and in this case "to make fire that brings light")

Carburators combine highly flammable gasoline with carefully measured amounts of air so that the engine produces just the right amount of power. An electronically created spark is created to ignite the combination of gas and air into an explosive burst of fire.

Ignite the atom!
Like angi also "nuclear fire" produces electromagnetic energy emitting heat and photons of light.

The fire is different, however, because the substance itself is "burning" without a reaction with another chemical. In fission reactions heavy atoms are splitting releasing enormous amounts of energy of the "weak force" that keeps molecules together. In fusion reaction lighter atoms join together into heavier atoms releasing plenty of energy in the process.

Scientists have shown that the "fire" burning in the main sequence stars is a fusion reaction in which the simplest elements of the Cosmos, hydrogen atoms, join to form the second simplest element, helium.

Ignite the hydrogen cloud!
Where is the spark that ignites one of the most desolate and cold things in the Universe, a dark cloud of hydrogen molecules and dust?

Well. Astrophysicists explain that there probably is no spark that ignites the process like the triggers used on earthly fusion bomb. Under certain conditions the hydrogen ignites itself in a thermonuclear process. To start "burning" into helium hydrogen must be heated to three million Kelvins. That is very hot but obviously this heating happens in the space. Known cosmos contains mostly hydrogen gas, the simplest element of creation with a single proton and electron. Yet, on the night sky we see with our own eyes thousands of these burning fire balls we call stars.

Molecular cloud of hydrogen is very sparse and its atoms have almost no movement as the temperature can be near absolute zero. So how it gets hot when it does so?

The mass of the hydrogen molecules is very small but they still have some mass. The fundamental force of gravity acts on these molecules pulling them together. First slowly but as the mass of the hydrogen lumps gets denser and atoms closer to each other the pull of the gravity gets stronger.

The idea in this theory of how stars are born from sparse clouds of hydrogen through gravity describes self-ignition. No cosmic spark is required, just a cloud of atoms and the force of gravity and some time. The gas collapses into itself forming a protostar which is a denser lump of atoms. The gravity causes the atoms to "fall" with increasing speed creating eventually the enormous heat required for the thermonuclear reaction to start.

It is not difficult to imagine that some heavy object might enter a cloud of hydrogen and begin a snowball effect gathering hydrogen atoms together like a magnet until the ball bursts into nuclear flames.

Stellar nurseries
Stars are born in clouds of hydrogen and dust. These dark birthplaces are lit by the new stars getting into fire inside the clouds themselves and also by reflecting light from neighbouring stars in different colors of the visible spectrum.

Some of the most famous astronomy photos have been taken of such dark nebulae, majestic stellar nurseries, where some of the most powerful processes in nature are taking place. One of the most famous stellar nurseries, Orion Nebula, is visible to unaided eye - the fabulous middle "star" in the dagger of Orion.

NASA Universe 101 teaches more!
There is much more to be learned about the birth of stars, about different kinds of stars out there and about the death of stars. A great source of information is from the leading centre of space exploaration NASA Universe 101

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