# How many neutrons are there in a teaspoonful of a neutron star and if stacked end on end, how far would these neutrons reach? [closed]

I am not a physicist nor a student of physics. I am just an old man that wonders. As such, I probably do not belong in this society. I've had a long interest in neutron stars. This interest began when a PBS scientist (physicist?) commented on a program (probably NOVA) that "a neutron star would be cool to the touch (about 80 degrees F), and a teaspoonful would have about the same mass as Mt. Everest". (I'm so sorry that I don't remember her name but the thought excited me.) Thank God (oops) that two neutron stars decided(?) to collide in my lifetime when it was possible that this collision was detectible. This collision (and its detection) created a new widespread interest in neutron stars. I'm sure that the data from this collision will be analyzed (and argued) for many years (long after I'm gone). And thank God (oops again) that the gravitational waves decided (ok, happened is a better word, but decided is sexier) to get here before the light did. That gave us enough time to locate it, film it, and analyze it. Ok, my ignorance is showing here and maybe this would have happened anyway. But I think it really convenient for us to get the gravitational waves first. Really? Earth size globs of gold and platinum. (Hitch up your wagons boys).

Truthfully, I'd rather not change my question. I don't mind anybody making their own assumptions as long as the math is correct. I expected (hoped) to get different answers. If a Physics Professor would ask this question (as it is) of his (her) class, all the answers (I believe) would be different. But this professor would have an opportunity to check the math and see the assumptions. (Ok, I admit that I am way out of my league here with that thought.) Perhaps that if those that voted to put my question on hold had answered my original question independently their answers would also be different. (Perhaps not, again way out of my league.) But really, I thank them for even looking at my question. My goal is to set a standard. If two people could (again independently) come up with the same answer, I could use that as a standard. Otherwise, if I could get enough answers I would use the average as a standard (jar of marbles). Why a standard? Well, if look up the subject on the internet, you'll get a bunch of different answers. Maybe I should just use those answers as my jar of marbles and leave you people alone. But for the little time I have been on this site, it is obvious to me that this is where the brains are. (and I have a lot of questions that could be answered here.) So I'll take the word "taken" out of my original question because this implies away from and ask the question this way. How many neutrons are there in a teaspoonful of a neutron star and if stacked end on end, how far would these neutrons reach? this is probably still unsatisfactory, But it is the essence of my question. Honestly, I'm already blown away by the few answers that I was allowed to receive. Really! There are enough of them suckers in a teaspoonful to reach hundreds of millions of light years?

## closed as off-topic by John Rennie, Rob Jeffries, stafusa, M. Enns, Jon CusterNov 1 '17 at 19:38

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• direct quote from wikipedia "A neutron star is so dense that one teaspoon (5 milliliters) of its material would have a mass over 5.5×1012 kg (that is 1100 tonnes per 1 nanolitre), about 900 times the mass of the Great Pyramid of Giza. ". – JMLCarter Nov 1 '17 at 18:15
• Hi and welcome to the Physics SE! Please note that you are expected to have thoroughly searched for an answer before asking your question. You can consider checking the advice on writing good questions. – stafusa Nov 1 '17 at 18:43

## 2 Answers

So 5.5 Pg of neutrons is $3.3 \times 10^{39}$ neutrons. Their diameter is 1.75 fm--so end-to-end:

5.75 Ym.

By basic calculation (forgetting neutron-neutron interactions) in one teaspoon there should be about 10^39 neutrons and if you take the classical proton radius as size, it would make a line of about 1000 000 light years in distance (more than 10 times the size of the galaxy).