What is the Interstellar Medium?

And how is it connected to everything else? 

by Mariah W.

What?

The Interstellar Medium, also known as ISM, is the gas and dust that is spread throughout all of interstellar space.

• ISM is made up of a highly dilute mixture of cosmic rays, ions, (galactic) magnetic fields, molecules, larger dust grains, and atoms.
• Its matter consists of about one percent dust and ninety nine percent gas by mass.
• The ISM has a very low density. 
• Fifteen percent of the visible matter in the Milky Way is composed of interstellar gas and dust. 
• Within the densest regions of the ISM  stars are formed.
• The ISM is replenished with matter and energy through supernovae, planetary nebular, and stellar winds.
• Breaking Down the words:

1. "Interstellar" - The word interstellar consists of two main prefixes, "inter-" which is means among, between, or amid and "-stellar" which means of or pertaining to stars or full stars. When combined the definition of interstellar is between or among the stars.
2. "Medium" - A medium is something that lies between or in the middle of things. It can also mean a substance through which an effect is transmitted from one thing or another. For example, when one speaks the waves of sound are carried by the air so the air is the medium through which sound travels! 
3. Putting it together - The interstellar medium is the material which is found between the stars. 

Since interstellar space means the matter that exists between the stars that are spread within a galaxy, interstellar dust is therefore found between the stars.  

Interstellar Dust-high concentrations produce diffuse nebulae and reflection nebulae 

Image credit: www.strw.leidenuniv.nl/~woitke/Bilder/Cycle_of_matter_small.jpg

When the interstellar dust forms a cloud with hydrogen gas and plasma it forms a nebula.

Nebula

A Nebula is an interstellar cloud of dust, hydrogen gas and plasma!

Nebulae can form star-forming regions in which dust, gas, and other materials clump together. These formations attract more matter and eventually become large enough to form stars and planets (as well as other planetary systems and objects)!

The Triangulum Emission Nebula NGC 604

The Cat's Eye Nebula,

an example of a planetary nebula.

Who?

Astronomers and Physicists are the ones who are most interested in learning about the interstellar medium at present. In the past there were many other people who contributed to the study of the IMS, like scientists and naturalists.

Definitions:

Interstellar: situated or occurring between the stars. 

The Interstellar Medium: (or ISM) is the gas and dust that spread(or spreads?) throughout all interstellar space. 

Interstellar Space: is the matter that exists between the stars that are within a galaxy.

Cosmic Dust: 

Interstellar Dust: is found between the stars

-When it forms a cloud with hydrogen gas and plasma it forms a nebula!

-high concentrations produce diffuse nebulae and reflection nebulae 

Sources and Links: 

en.wikipedia.org/wiki/Interstellar_gas

dictionary.reference.com/browse/interstellar

en.wikipedia.org/wiki/Dust#Atmospheric_dust

en.wikipedia.org/wiki/Nebula

www.strw.leidenuniv.nl/~woitke/Bilder/Cycle_of_matter_small.jpg