Let's go!
Immediately after the Big Bang, I was formed through the collision of two gamma rays. Not only was I formed, but a positron, my brother Ulysses, was also formed. The diagram below shows how this happens.
After floating around alone for about 3 minutes, I was cool enough to form a hydrogen atom with a single proton. The residual force from the Big Bang had so much energy and was so hot, we were sent flying off into space at a speed close to that of light (which is 3 x 10^8 meters/second!). That's really fast! Sometime later, we passed by a large cloud of gas. This cloud was so massive and had so much gravity that we were immediately pulled right into it! There were so many atoms there - about 10^24 other atoms, to be exact! The gravity acting on all of us packed in there together became greater than our ability to push outward on the others. Also, this squishing of us all into a very small space (relatively speaking) forced us to collide with each other more often, raising our temperature. Once it got really hot (100 million degrees centigrade), we started a process called fusion. Fusion occurs when two or more atoms combine to form a heavier atom, giving off tremendous amounts of energy. The diagram below illustrates the following principle.
TWo hydrogen atoms combine to form a 2H , a neutrino (a particle that has very little mass), and a positron (much like my brother Ulysses). The molecule combines with another H atom to form a 3He molecule and at the same time gives off gamma radiation. Two 3He molecules combine to form an 4He molecule and 2 hydrogen atoms. That simple reaction requires high temperatures, and it sure gives off a lot of energy!!!
We (my fellow hydrogen atoms and I) had formed a star! The winds generated by all those charged particles we released cleared the area around us for 3 astronomical units!!! In case you didn't know, an astronomical unit is the distance between the earth and the sun - around 1.499 x 10^11 meters.
We had a happy life there in our little star. Through fusion, we turned our hydrogen into helium to give off energy and light. As we formed helium, we began to differentiate between hydrogen and helium and formed layers around our core. This picture shows basically what our star looked like on the inside.
The convection
zone has currents that carry heat from the interior of the star to its
surface. Cooler material sinks downward.