Interstellar medium

Definition

Interstellar medium (ISM) is the matter that exists in the space between star systems within a galaxy. It consists of gas (both ionized and neutral) and dust, playing a crucial role in the life cycle of cosmic material.

5 Must Know Facts For Your Next Test

1. The interstellar medium is composed mainly of hydrogen and helium, with traces of heavier elements.
2. It has very low density, typically less than one atom per cubic centimeter.
3. Regions of the ISM can be classified into different phases based on temperature and density, such as cold molecular clouds or hot ionized gas.
4. Interstellar dust grains contribute to the extinction and reddening of starlight as it passes through the ISM.
5. The ISM is essential for star formation, providing the raw materials needed to form new stars.

Review Questions

Related terms

Nebula:

A nebula is a cloud of gas and dust in space, often forming regions where new stars are born.

Molecular Cloud:

A type of interstellar cloud whose density and size permit the formation of molecules, particularly hydrogen.

Extinction:

Extinction refers to the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer.