What is a giant molecular cloud?
Large, dense molecular clouds are very special environments in space. Composed mainly of molecular hydrogen and helium, with small amounts of heavier gases, they are the birth place of new stars and planets. Molecular clouds that exceed the mass of 100,000 suns are called giant molecular clouds. Giant molecular clouds are the largest inhabitants of galaxies, reaching up to 300 light-years in diameter. They contain enough dense gas and dust to form hundreds of thousands of Sun-like stars. These stars are formed in the densest parts of the clouds. Molecular clouds are very cold, having temperatures ranging from about -440 to -370 degrees Fahrenheit (-263 to -223 degrees Celsius or 10 to 50 degrees Kelvin). They usually do not radiate their own visible light and appear dark when viewed with an optical telescope. In these cold, dense environments, many atoms can combine into molecules. Giant molecular clouds can last for 10 to 100 million years before they dissipate, due to the heat and st