Rita Surana, age13, of Vancouver, British Columbia, for her question:
How can stars burn if there is no oxygen in space?
A generation ago, we assumed that the infinity beyond the earth's atmosphere was an empty void. Now we know that space is filled with gaseous plasma. But, it does not have enough oxygen to support a campfire, let alone a star sized furnace. Nevertheless, the spaces of our Galaxy are populated with 100 billion blazing stars.
When we think of fire, we keep in mind the oxygen gas needed to keep it burning. This is the ordinary type fire that consumes coal or logs. But even on our earth we have other furnaces that shed heat without consuming these burnable fuels. We can bake our bread in electric ovens and cook our food on electric stoves. These electric furnaces do not burn coal type fuels, nor do they need to be fed with continuous drafts of gaseous oxygen. They shed light and give off heat from electrons moving through circuits of copper wire. The stars, however, are not powered by cosmic electric generators. But their fiery fur¬naces need no oxygen.
Suppose an average star were made of good grade coal, placed inside a dense earth type atmosphere and set on fire. Its cosmic coal fire would blaze cheerfully for perhaps 5,000 years. Then its fuel would be consumed, leaving only a cosmic dustbin of cold, dead ashes. We know that the stars have been twinkling for ages and some of their fiery furnaces have been blazing for billions of years. So they cannot be ordinary fires that consume coal type fuels with the help of oxygen. We now know that they are nuclear powerhouses that work somewhat like continuously exploding hydrogen bombs.
This type of atomic activity is called nuclear fusion. Actually it is the fusion or welding of the nuclei of small atoms to form nuclei of larger atoms. The small atoms pro¬vide the fuel for the starry furnace. The larger atoms are the waste ashes of the operation. The process occurs in minuscule units, deep within the fiery heart of the star, where temperatures reach at least 27 million degrees. In these seething conditions, all electrons are stripped from their parent atoms. The starry furnace is densely packed with ions, or atomic nuclei.
Most experts agree that each unit of activity involves. four hydrogen ions. Hydrogen is the smallest of all atoms, with but one proton in its nucleus. In the core of a star, the four smaller hydrogen ions are thought to fuse into one helium ion. When the four hydrogen ions fuse together, there is a slight surplus of material left over. This is released as nuclear energy. Countless billions of these small nuclear fusions occur every moment and together they release the radiant energy that streams from the blazing star.
The steps by which hydrogen converts itself into helium are very complex and though several theories have been suggested, none has been proved in detail. But the thermonuclear activity does require the seething conditions found in the core of a star. It requires hydro¬gen, enormous supplies of hydrogen to use as fuel. But since a star is made mostly of hydrogen, this is no problem. But the starry power plant needs no oxygen to keep it going.
A young star is made almost entirely of hydrogen gas. It may consume up to 564 million tons of its fuel every second, converting it into about 560 million tons of helium ashes. The four million tons of material lost in the shuffle are converted into seething nuclear energy and poured forth in all directions across the vast reaches of space. The star con¬tinues to blaze as long as it has hydrogen to feed its fiery furnace. Finally, after many billions of years. the fuel runs out and the starry furnace is choked with "ashes" of helium.