ASK A SCIENTIST
Question: How was the sun formed?
This is one of my favorite questions because the answer is something that just about all scientists agree on, and one that helps us understand our existence.
The sun is a star, and although special to us, it is an ordinary dwarf star in our galaxy, the Milky Way, and in the Universe. It is a second-generation star, or metal-rich star, which means it was formed out of material that came from other stars.
At sometime in the past, about 5 billion years ago, there was a cold cloud of gas consisting mostly of hydrogen and helium in our part of the Milky Way. Nearby, a massive star, several times the mass of our sun, was going through the last stages of its life. Eventually, the nearby star exploded, what is called a supernova, and sent waves of matter out in all directions. Some of this matter collided with the cold cloud and triggered the start of the collapse of the cloud into our sun.
Another important thing that the collision did was to add heavy elements to the cloud. These heavy elements were made in the exploding star. Massive stars are the source of all the heavy elements in the Universe. This adding of the elements is important because the material the planets are made from is material leftover from the forming of the sun. Where would we be without copper, iron, or oxygen, for example?
Once the cloud started to collapse, it continued to do so for about 1,000,000 years forming into a ball of hot gas. No one was around with a stopwatch, so this time is based on studying a lot of stars and understanding how they work. The center of the ball kept getting hotter until it got hot enough for the hydrogen in the center of the ball to start fusing into helium. Fusion is when hydrogen atoms (four of them, actually the nuclei of hydrogen atoms) come together under high temperature and pressure conditions to form into one helium atom. Once fusion starts, the sun pretty much stops collapsing.
Fusion is a source of energy and is sometimes called "hydrogen burning", but it is not really burning as though it was on fire. What is neat about this fusion process is that some of the energy contained in the atoms is released. This released energy flows from the center of the sun out into the solar system. This is the energy we depend on from the sun for light and heat.
Once the process of fusion starts, the sun is then a normal star what astronomers call a main sequence star. The sun is a normal star for as long as there is hydrogen in its center to fuse into helium. The sun is believed to be about five billion years old and is expected to be a main sequence star for another five billion years. At that point, changes will start to take place inside the sun, but that is another story.
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