What is the difference between protostars and normal stars and how do we know about them?
What is a nebula?
The life cycle of a star starts of with a cloud of gas and dust. Dust and gas clouds are nebula (more than nebula is called nebulae). There are a few types of nebula. They are Planetary nebula, Dark Nebula, Reflective nebula and emissions nebula. Planetary nebula usually surround a nova or super nova (nova is when a star becomes thousands of times hotter and brighter and a supernova is when a star becomes billions of times hotter and brighter).Dark nebula are gas and dust clouds that that block all the light from the stars behind them out so we cannot see what is behind them. Reflective nebula are a bit alike dark nebula because they reflect all the light from around them so they appear really bright.
How does nebula form protostars?
Over millions and millions and millions of years the nebula starts to compact and become much more dense and eventually become more dense that a ball of steel. As it becomes denser it also becomes hotter and starts to glow. This is now what is called a protostar. Protostars have a few different classes the youngest of them is class 0 proto stars. They are about 100,000 years into its life. The temperature on their surface is about -260°C. After a few million years from then it becomes a star. Gravity was first thought to collapse the nebula so it can start to become a protostar but radiation has from a young star has started the theory that it might be something else.
A few facts about the sun and stars
The sun is 97% hydrogen and 3% helium.
The sun 15,000,000°C.
Old stars often shoot out dust and gas clouds (nebula).
There are blue, white, orange and yellow stars.
Stars can be twins just like us.
The sun is so big it could fit 333,000 earths inside it.
The sun appears small because it is 15 million km away from earth.
References:
http;//www.nasa.gov/vision/universe/stargalaxies/xmm_magnetic_starbirth.html, written by Lynn Jenner, last updated 30 November 2007, accessed on 16/6/2010
World books childcraft: The Universe Publisher World Book Inc. By James Conahan, Herb Herrick and Nigel sharp. PP 129, 10 and 13