Our star, we call it the Sun. The Sun is a star. Itís just so large because weíre so close to it, only 93 million miles away is the Earth from the Sun. Our star is just under a million miles in diameter. At 850,000 miles from one side to the other, itís only 150,000 short of being a million miles in diameter. I like thinking to myself that if I ever wondered what a million miles looked like I could look at the Sun and add just a little to the edge to make it a little bit wider and say, ďthatís what a million miles looks like from 93 million miles away.Ē Just shy of a million miles is our star. It sounds huge but our star is middle of the road when it comes to the size of stars.
The majority of stars are red dwarf stars that are smaller than half the size of the Sun. Others stars are giants. Take the red giant Betelgeuse in the constellation of Orion. This star is 600,000,000 (600 million) miles in diameter. Compare that to our star at 850,000 miles in diameter and you begin to realize what big really is. Astronomers recently found three stars with diameters over a billion miles.
If one edge of Betelgeuse was where our Sun is, the other edge would be out where Jupiter is as Jupiter is 600 million miles from the Sun. It is a huge star but it also is a star with a very short life. Stars this big burn their hydrogen so fast, their lives can be as short as 100,000 years.
Stars form inside huge gas clouds of hydrogen atoms made from the heat of the Big Bang or gas clouds that were formed when first or second generation stars threw their mass into space in a nova or super nova explosions. In time, gravity pulls the gases closer and closer until the atoms begin knocking into each other and begin to stick together. Over time the clumps of atoms get larger and larger until their mass is so great that the pressure at the center of these balls of gas builds up heat to a temperature where nuclear fusion begins, combining hydrogen atoms to make helium atoms and heavier elements. Every time two hydrogen atoms combine it creates a photon of light and the star shines. The Sun converts 400,000 tons of hydrogen a second into helium by combining two hydrogen protons.
Stars like our Sun will burn their fuel at a slower pace and will live in their prime phase for about 10 billion years before it begins to run out of hydrogen fuel and the gravity weakens. At this point the Sun will shed most of its mass into space leaving behind its core. Smaller stars such as red dwarf stars burn their fuel slower and will have lives as long as 60 billion years or more. The Universe is 14 to 15 billion years old so these stars, even if they were formed in the early Universe are still only in their adolescence and will live after the Earth and Sun are long gone.
The way a star forms is quite simple and well understood. With our knowledge of stars, we can look at almost any star and gather information from its light sources such as in visible, x-ray, ultraviolet, hydrogen and infrared lights to name a few, and tell almost precisely where the star is in its life cycle and what elements are being formed inside the star.
One of the strangest things known happens to stars with the greatest mass. In stars with enough mass, the gravity is so strong that nothing can stop the gravity from collapsing in on itself. Gravity pulls these atoms closer and closer and tighter and tighter until the star vanishes from space and leaves behind a hole in space, a black hole. The gravity of a black hole is so dense and strong that not even light can escape the gravity. What happens to the matter that falls into a black hole we donít yet know but given time we will eventually figure it out.