Test Your Knowledge on Star Formation and Interstellar Medium

Star Formation and Interstellar Medium: Understanding the Birth of Stars

• Stars form in dense molecular clouds within galaxies, where recent advances in radio and infrared astronomy allow astronomers to study the processes involved in star birth.
• Nebulae are clouds of interstellar gas and dust, which appear as dark regions blotting out background stars or as brighter clouds of gas that emit or reflect light.
• The interstellar medium (ISM) fills the space between the stars and provides the building blocks of stars, which are predominantly hydrogen gas and dust made up of carbon compounds and silicates.
• The properties of the ISM vary widely depending on its location within a galaxy, with densities ranging from 100 particles per m3 to 1017 particles per m3.
• Giant molecular clouds (GMCs) are regions of the ISM where stars form, containing large amounts of matter, mainly molecular hydrogen gas, and other molecules such as water, carbon monoxide, ammonia, and methanol.
• Dust within GMCs blocks out starlight, keeping the clouds cold at around 10-30 K, and is studied by the characteristic emissions from CO molecules at mm wavelengths in the radio waveband.
• GMCs tend to be concentrated along the spiral arms of spiral galaxies, such as our own Milky Way, and can be seen as dark dust bands in the arms.
• Emission nebulae are clouds of dust and gas that shine due to the emission of their own light, and there are three main types: HII regions, planetary nebulae, and supernova remnants.
• HII regions are associated with star birth regions, display distinctive red and green colors, and are caused by hydrogen-alpha emission and forbidden transitions of singly-ionized nitrogen and doubly-ionized oxygen ions.
• The intense radiation released by hot, young stars within or close to the nebula eventually sweeps away the dust and gas, leaving the stars exposed.
• Gravity is responsible for stellar formation, and the mass of material that forms a star largely determines its life and fate.
• Computationally intensive computer simulations allow astronomers to model the processes of star formation and test the results against observations.