Expert Answers
pacorz eNotes educator| Certified Educator

Stars are made in nebulae, not from them. A nebula is a thick cloud of dust and gas in space. As the particles of the nebula swirl around, they may bump into each other. Because every object in the universe has gravity in proportion to its mass, particles that touch are likely to stick together, forming a larger particle with more gravity. This larger particle can then attract more particles, growing bigger and bigger. Once the mass has gotten large enough, the friction of the molecules rubbing together causes internal heat to begin to build up, and the object becomes a pre-main sequence star. If the mass gets hot enough it can ignite the hydrogen gas, and the new-born star enters the main sequence. The burning of hydrogen releases energy which causes the star to  begin nuclear fusion, converting hydrogen into helium. The star's lifespan is determined by how much material it accumulates before it ignites. Our sun is a mid-sized star, and is currently about halfway through its 10 billion year lifespan.

cntryfrog eNotes educator| Certified Educator

Stars begin as a nebula, a cloud of gas and dust.  As the nebula begins to contract or condense, it heats up and starts to burn.  Usually, the first stage is a "main sequence" star which is fueled by the process of nuclear fusion of hydrogen into helium.  Depending on the mass of the star, the star will take a different path in it's life cycle.  Just as an example, our Sun is a main sequence star.

astrosonu | Student

Stars begin in a nebula, a cloud of gas and dust.

astrosonuthird | Student

Stars are formed inside a nebula, when the nebula contractes, it becomes more and more dense so this is how stars are formed by the fusion of hydrogen and helium it carries out its life process.