Except on Earth,
the Milky
Way galaxy
doesn't contain
any milk. But it sure does have a lot of
calcium. There's enough calcium floating
between the stars to fortify trillions upon trillions
of gallons of milk.

Calcium comes from stars. In fact, all of the
elements that make up your body and the
planet Earth itself, other than hydrogen and
helium, were made in stars or during
explosions of massive stars.

Stars are like mighty chemical factories.
They burn hydrogen and helium through a
process of nuclear fusion, which produces a
tremendous amount of heat energy. In addition to energy, the fusion process in massive stars (stars having more than 8 times the mass of our sun) results in carbon, nitrogen, iron and other atoms. As iron accumulates in the stellar core, the fusion process no longer produces heat energy.  At this point in the life of a massive star, the core collapses and the star explodes, sending all those atoms racing into space.  Some atoms bump into each other in the fury, fusing to create even heavier atoms such as gold, silver and uranium. These atoms spread across the galaxy over the course of billions of years.

Cassiopeia A is a star that exploded about
320 years ago. No astronomer recorded the
explosion at the time, but we can still see the
remains of the explosion today in the form of
a colorful supernova remnant.  By measuring the motion of the gas in the remnant, astronomers deduce its age.

The Michigan-Dartmouth-Massachusetts
Institute of Technology Observatory on Kitt
Peak, Arizona, captured a beautiful image
of Cassiopeia A in visible light (above, top.
In an image accumulated over a million seconds, The Chandra X-ray Observatory, an earth-orbiting satellite, saw the hot X-ray-emitting
gas from the explosion (on front, and middle
image, this page). This gas is hotter than the
surface of the sun. Chandra was also able to
see the individual elements within the explosion.
For example, researchers at NASA's
Goddard Space Flight Center created an
image showing only the element calcium
(bottom image).



For the classroom:

How much calcium is in Cassiopeia A?
Use the following information to find out:

 The star that produced the supernova remnant
Cassiopeia A was about 20 times more massive than the Sun. It was largely made up of hydrogen but also contained some calcium and other elements. 

 When the star exploded, the hydrogen,
calcium, and other elements produced by fusion during the life of the star fly off into space.  The explosion creates more of these and other elements. The total amount of calcium is equal to about 0.05% of the mass of the original star.

 One glass of milk (8 fluid oz. or 237 ml)
contains approximately 300 mg of calcium.

Using this information, 
1) How many kilograms of calcium are in a typical supernova remnant, like Cassiopeia A? 
2) How many 8-ounce glasses of milk would this equal? 
3) How long must the cows in the United States be milked to produce this number of glasses of milk? 

For the answer to the "For the Classroom" questions, see http://imagine.gsfc.nasa.gov/docs/teachers/calcium

For more information on supernovae and supernova remnants, see:

http://imagine.gsfc.nasa.gov/
http://chandra.harvard.edu/xray_sources/supernovas.html



Figure Captions:
Optical: Visible Light image of Cassiopeia A (from a telescope on Earth)

1st X-ray Image: X-ray image of Cassiopeia A (from Chandra X-ray Observatory)

2nd X-ray Image: [OK as is]