Home Lesson for Students

The CHIPS mission is studying the stuff in the huge spaces between the stars known as the Interstellar Medium, or ISM.  


Is there really anything out there?

Is it interesting stuff?


The ISM - What on Earth is it?

Most of us,  at one time or another,  have learned that space is perfectly empty.  But what do we mean by "empty"?  We often say that a bottle is empty if there is no water or soda pop in it - but just how empty is that bottle?

Try this: Take a plastic bag (with no holes in it!) and tape the opening of the bag around the mouth of a jar - make sure the bag is taped tightly! Now try to push the bag into the jar...

Why is it so hard to push the bag into the jar?  Because the bottle is not really empty - it is full of air!  It is tempting to think of air as "nothing" - but air is really "something".  Inside the jar were many, many billions of air molecules.  The molecules are far too small to see - but the experiment you just did (or imagined doing) with the jar is pretty good evidence that they are there.  After all,  something was preventing you from pushing that bag into the jar!

The air around us (just like the air in the bottle) is a gas made up of different kinds of molecules - mostly nitrogen, hydrogen, and oxygen.  Out in the huge spaces between the stars,  there is another kind of gas - mainly hydrogen and helium - sprinkled with very tiny grains of dust.  This gas is much more spread out,  or diffuse,  than the air we breathe - and much, MUCH hotter (even hotter than the surface of the sun!).


So outer space is not really empty at all. The 'stuff' in the vast spaces between the stars is known as the Interstellar Medium (or ISM). This picture (left) shows a gold colored cloud of gas in the ISM, glowing with the energy that it gets from nearby stars.

The Local Bubble: Our astronomical neighborhood

Our solar system is located in an unusual region of space called the Local Bubble.  This area is called the Local Bubble because the ISM in this area is much less dense than the ISM surrounding it.  The gas is also extremely hot - about one million degrees,  or almost 200 times as hot as the surface of the sun!  Scientists believe that this bubble may have been created by a star that exploded.  These huge explosions - called supernovae - happen when very large stars run out of energy and die.  Supernovae send huge amounts of stuff out into space in all directions - this stuff becomes part of the ISM.  Many billions of years later,  this stuff can clump together,  cool off,  and become a new star - and the cycle starts all over again.

The picture below shows a supernova that exploded in 1987.  The small pictures at the bottom show how the star at the center of this supernova changed from February on 1994 to February on 1996.  Can you see how it gets more fuzzy?  The debris from this explosion is traveling through space at 6 million miles an hour!

To get an idea of how the Local Bubble may have been formed,  try this:  spread a small amount of flour or fine sand on a flat dish.  Now blow (gently) through the straw on the flour.  You'll notice that a hole forms,  and that the flour piles up in a ridge around this hole.  If you were to look closely,  you would probably find a few grains of flour in the hole.  This is something like how the Local Bubble formed - a supernova explosion "blew" most of the gas and dust from the interstellar medium outward.  Some of the remaining gas and dust cooled and clumped together  to form the stars and planets in our local area of space.  In fact,  this dust makes up our whole planet and everything that has ever been on it.  Look around you - everything you see was once this dust,  even the molecules that make up YOU!

The CHIPS mission is going to study the ISM in the Local Bubble,  in the hopes that it will tell us something about how stars form in our universe. 


>>Learn more about the ISM...