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Q & A: Neutron Stars, White Dwarfs and Red Giants

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Most recent answer: 10/22/2007
Q:
I have heard that a teaspoon of the core of a white dwarf star weighs a few billion tons. And I am wondring how much a teaspoon of a red giant would weigh.
- James Selen (age 12)
Urbana Middle School, Urbana ,IL , U.S.A
A:
James,

Thank you for your question.

What you have probably heard is that the core of a "Neutron Star" is so dense that even a small amount, like a few teaspoons full, weighs about a billion tons. This is actually true!

As you probably know, normal matter (like people, trees and rocks) is made of atoms. Even though atoms are very small, they have an even smaller thing inside them called a nucleus. The nucleus inside an atom is so small that if you made a model of an atom that was the size of a house, the nucleus would still only be the size of a grain of salt. The interesting thing about the nucleus is that it is where almost all of the weight of an atom is concentrated.

In a neutron star, all of the atoms have been squashed together so tightly by the force of gravity that their nuclei are touching (think of a bag of marbles). Since each of the tiny nuclei still weighs almost as much as a whole atom normally would, and since they are very small (meaning lots of them fit in a small space), a small scoop of a neutron star is extremely heavy.

A neutron star is what is sometimes left over when a very heavy star explodes. This explosion is called a Supernova, which you may have heard about also. Below is a nice picture of a neutron star inside the gassy looking remnants of a supernova called Puppis A. This is from a very interesting NASA website you can find at: http://lheawww.gsfc.nasa.gov/users/jonathan/snr_group/Puppis_A.html)


A Red Giant is what our own Sun will become one day a very long time from now (a few billion years). When this happens it will swell up and get so large that the orbit of the earth will actually be inside the sun! Since the sun will still weigh about as much in the future as it does now, but it will be taking up much more space, it's weight will have to be very spread out. A spoon-full of material taken from a red giant (except at it's very center) will not be heavy at all, weighing much less than a small grain of salt.

If you waited many more millions of years after our sun has become a red giant you would see a white dwarf. A white dwarf more or less what was hiding in the center of the red giant all the time but was covered by it's huge red "atmosphere". A white dwarf is much more tightly packed than a red giant, but is not as tightly packed as a neutron star. A teaspoon of material from a white dwarf would weigh about one ton or so.

(published on 10/22/2007)

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