Star Stuff™
"Density of Space"
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Interstellar Dust

Fascinating Fact: A teaspoon of neutron star material weighs about 110 million tons.

"Space, the final frontier."  Those are the words that might come to mind when you gaze up at the stars on a clear night,  but wait a second  -- what is that dark "void" that separates the stars? If you said, "space", then you are partially correct. Outer space is divided into many levels and the one that separates the stars is called interstellar space.

It is often a misconception that space is a vacuum or simply empty. Space is a nearly perfect vacuum, even better than the best ones made in labs on earth, but it is not devoid of everything. The fact is that space is filled with tiny particles called cosmic dust and elements like hydrogen and helium. This applies for interstellar space also and all the previously mention particles make up what is known as the "interstellar medium".

The interstellar medium is mainly made of lone hydrogen atoms. They do not even exist as pairs as they do on earth. I mentioned before that space is filled with hydrogen atoms. The actual density of hydrogen as it exist in interstellar space is on the average of about 1 atom per cubic centimeter. In the extremes, as low as 0.1 atom per cubic centimeter has been found in the space between the spiral arms and as high as 1000 atoms per cubic centimeter are known to exist near the galactic core.

The interstellar medium also contains cosmic dust. These particles are much bigger than hydrogen atoms. However, there are far fewer particles of cosmic dust than there are hydrogen atoms in the same volume of space. It is estimated that cosmic dust is 1000 times less common than hydrogen atoms in the interstellar medium.

Fascinating Fact: A Red Giant (a type of exploded star) has a lower density than any vacuum created here on earth.