# Thread: Neutron Star Neutron Spacing

1. Newbie
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Aug 2003
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I have read that neutron stars weigh thousands of tons per cubic cm. I wanted to verify this. I assumed the neutrons are spheres and basically touch each other with a packing factor of 65%. I divided the mass of a neutron by its volume and multiplied by 0.65 (the packing factor). Unless I made an error, the result is BILLIONS of tons per cubic cm, not thousands. So what is the spacing of neutrons in neutron stars, and what keeps them separated at this spacing?

2. Member
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Jul 2003
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31
What gives a nutron star its density is that there is no space between the nutrons. They have all been colapsed into one unit: The star.

3. Newbie
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Aug 2003
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First of all, you missed my point but I will get to that later. It looks like the value I used for the neutron radius in my original calculation was a very rough approximation. Although neutron mass is well known, it appears the radius depends on many factors. I have since found two values for "nuclear density": 2.0E+14 g/cm^3 and 2.8E+14 g/cm^3. Still assuming the neutrons are touching with my original packing factor of 65%, and recognizing that the volume of a teaspoon (the ubiquitous unit of neutron star volume used in many lay articles) is 4.92 cm^3, then a teaspoon of neutron star will weigh between 705,000,000 tons and 987,000,000 tons. My point was that if a teaspoon full weighs nearly a billion tons, then why do all these articles keep saying that a teaspoon full weighs thousands of tons. If a teaspoon really weighs only thousands of tons (and presumably “thousands” means far less than a million) and not a billion tons as my close-packing calculation shows, then there must be significant space between the neutrons in a neutron star. That was my point that led to the question about the space between the neutrons. I hope that clarifies it.

4. Newbie
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Jul 2003
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Let me take a stab at this. Neutron stars are extremely hot, which puts the neutrons into an extremely excited quantum state. Your typical atomic nucleus is in a very low energy state, so that the neutrons and protons are packed much more closely.

5. Member
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Jul 2003
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31
"So what is the spacing of neutrons in neutron stars, and what keeps them separated at this spacing?"

This was the question I answered. "There is no spacing." Sorry I missed your point.

"My point was that if a teaspoon full weighs nearly a billion tons, then why do all these articles keep saying that a teaspoon full weighs thousands of tons."

My answer to this question is that these articles mess up on their data rather frequently. Mars is quite popular right now. I have seen articles that say it has not been this close for (500 to 6,000,000) Years. Obviously many of those people do not understand what they are talking about.

My suggestion is to never consider what you read to be valid until you find at least several varied sources that agree.

Bud

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