When will the
sun die?
The Sunday Nation
Nairobi,
07 November 2010
Alex Nduva is
concerned that the sun will burn out soon. He writes: “The sun comprises
of burning gases. For the millions of years that it has been in
existence, the gases have never been exhausted. Will there come a time
when we shall not have this natural energy courtesy of the sun?”
Alex, the basis of
your reasoning is not correct. The sun does not comprise of burning
gases. Burning is the mixing of a fuel with oxygen in a reaction that
produces energy. This is not what happens in the sun. In fact, there is
no oxygen in there.
The sun uses a better
method to generate energy. It destroys matter! O.K.; I know that basic
science teaches that matter cannot be created nor destroyed, but that
statement is not entirely accurate.
About 100 years ago,
Albert Einstein showed that matter can be destroyed and converted into
energy. That’s the meaning of his famous equation: “energy equals
m-c-squared”. It also means that energy can be destroyed and converted
into matter.
Every second, 700 million tonnes of
hydrogen are converted into 695 million tonnes of helium at the centre
of the sun. The missing 5 million tonnes are converted into energy and
radiated into space.
The rate of energy
release is about 400 trillion-trillion watts. That is; the number 4
followed by 26 zeroes! No wonder it feels very hot even on earth – 150
million kilometers away.
Now, 700 million tones per second works out to about 20,000 trillion tonnes per year. We can now appreciate the source of Alex’s concern – this is a very high rate of consuming fuel.
However, the mass of the sun is about 2,000 trillion-trillion tonnes at present. That is, the number 2 followed by 27 zeroes. Hydrogen accounts for about 75 percent of this, or 1,500 trillion-trillion tonnes.
At the rate of 20,000 trillion tonnes per year, the remaining hydrogen will last… 1,500 trillion-trillion divided by 20,000 trillion… equals about 75 billion years!
By that time, many things will have changed in the universe; therefore, we really don’t have to worry about it. However, even though the sun has enough hydrogen to last 75 billion years, it is not likely to stay that long in its present form.
Scientists believe that in about 5 billion years, the main reaction in the sun will not be the conversion of hydrogen to helium. It will be turning helium into carbon. When that phase is reached, the sun will balloon into a huge giant star measuring about 350 million kilometres.
The first four planets, Mercury, Venus, Earth and Mars will all be swallowed into this giant star. Nonetheless, I am not worried one bit by a calamity that might come 5 billion years from now!
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