# Neutron star question (again) **URL:** \ **Category:** Factual Questions\ **Created:** [November 12, 2002, 4:42am UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384 "2002-11-12T04:42:17Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [November 13, 2002, 11:24am UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/21 "2002-11-13T11:24:45Z")
> [@](#): > > scotth: I totally agree that Bad Astronomer should write a book. For those who don’t know, [he’s already written one.](http://www.amazon.com/exec/obidos/ASIN/0471409766/qid=1002324596/sr=1-3/ref=sr_1_0_3/103-7192648-5486217/badastronomy) (I think scotth was suggesting he write a second one.) ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 1:26pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/22 "2002-11-13T13:26:19Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\* > > For those who don’t know, [he’s already written one.](http://www.amazon.com/exec/obidos/ASIN/0471409766/qid=1002324596/sr=1-3/ref=sr_1_0_3/103-7192648-5486217/badastronomy) (I think scotth was suggesting he write a second one.) \*\* Quite right. And in case it wasn’t clear (it seemed clear last nite)… The book should be a collection of small personal discovery stories like the one he shared in this thread. More of his, and other ones collected from colleages. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 13, 2002, 3:24pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/23 "2002-11-13T15:24:25Z")
Just as a thought experiment: Assume you could strip away the outer layers of a Neutron Star and expose the neutronium underneath (and assume it would remain neutronium…I’m guessing that’s the proper term for that material). Would the Neutron Star be dark? That is, can neutronium glow? My understanding is you need electrons changing orbits to create light. In neutronium the electrons are all crammed into the nucleus of atoms so they can’t be jumping about. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 3:38pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/24 "2002-11-13T15:38:47Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*Just as a thought experiment: > > Assume you could strip away the outer layers of a Neutron Star and expose the neutronium underneath (and assume it would remain neutronium…I’m guessing that’s the proper term for that material). > > Would the Neutron Star be dark? That is, can neutronium glow? My understanding is you need electrons changing orbits to create light. In neutronium the electrons are all crammed into the nucleus of atoms so they can’t be jumping about. \*\* Hah, busted Whack-a-Mole not reading the whole thread… (Just messin’ with ya)… but that was my question above, just phrased a bit different. > [@](#): > > If the neutron star actually had exposed neutons (neutrons stars are expect to have some thickness of normal matter on their surfaces), I can’t imagine how light would interact with it. Light only couples with charge carrying particles. Neutrons don’t have a charge. Would it be transparent? Doesn’t seem likely to me, but I don’t know. and the response: > [@](#): > > I thought this at first, too, but sadly I don’t think it’s true. Neutrons do have a charge quadrupole moment, so photons and neutrons can interact. Neutronium isn’t transparent. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 13, 2002, 3:46pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/25 "2002-11-13T15:46:04Z")
> [@](#): > > \*Originally posted by scotth \* > \*\*Hah, busted Whack-a-Mole not reading the whole thread… (Just messin’ with ya)… but that was my question above, just phrased a bit different. \*\* I don’t think so. I read your thread and the response and it seemed like it was asking how neutronium _reflects_ light. I’m asking whether it can _produce_ (or emit) light. It’s weird to think of an incredibly hot ball being as dark as midnight which is what I was getting at. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 3:58pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/26 "2002-11-13T15:58:46Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\* > > I don’t think so. I read your thread and the response and it seemed like it was asking how neutronium _reflects_ light. I’m asking whether it can _produce_ (or emit) light. It’s weird to think of an incredibly hot ball being as dark as midnight which is what I was getting at. \*\* Missed that finer point… I had considered those in the same thought process in the past… I was considering that all interaction with light (by basis of a charged particle) would be solved together or not. ---
**Author:** ![cdhostage](https://avatars.discourse-cdn.com/v4/letter/c/c6cbf5/32.png) [@cdhostage](https://boards.straightdope.com/u/cdhostage)\ **Post date:** [November 13, 2002, 6:28pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/27 "2002-11-13T18:28:44Z")
Wait a second. Assume that we have a sphere of nothin’ but neutronium - let’s assume there’s no normal matter getting in our sightline. It has been a neutronium star for a relatively short amount of time (yes, I know it would attract anything nearby and convert most of it to neutronium w/ a layer of normal plasma - quiet). It is very very hot. I have no idea how hot, but the neutrons are probably bumping against eachother as vigourously as do the particles in the center of a star. It is spinning at a fast rate. What effects does this object have on its surroundings and what does it radiate? ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 6:45pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/28 "2002-11-13T18:45:08Z")
I would love to understand this process as well. I feel certain that I will be hitting the books some more to prepare myself to understand the answer. It is one thing to have an answer, and another to actually understand that answer. I don’t think I am really ready to understand it yet. If I was, I could probably deduce it for myself. For example: “Neutrons do have a charge quadrupole moment” Ok, but I don’t undertand how. ---
**Author:** ![JS\_Princeton](https://avatars.discourse-cdn.com/v4/letter/j/57b2e6/32.png) [@JS\_Princeton](https://boards.straightdope.com/u/JS_Princeton)\ **Post date:** [November 13, 2002, 7:09pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/29 "2002-11-13T19:09:47Z")
Neutron stars radiate in the radio. That’s what a pulsar is. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 7:45pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/30 "2002-11-13T19:45:14Z")
> [@](#): > > \*Originally posted by JS Princeton \* > \*\*Neutron stars radiate in the radio. That’s what a pulsar is. \*\* No problem with that statement… But, here is my confusion. Radio is still photons. Photons (to my understanding) only interact with charged particles. Neutrons have no charge. If your statement is true (and I don’t doubt that it is), it reveals to me that my understanding of photon-particle interactions is incomplete. My first guess would be that the photos could interact with sub atomic particles that make up a neutron. All of which have a (fractional) charge. But, I still feel I have more studying to do to really grasp how this might happen or if indeed this is the correct answer. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 13, 2002, 8:51pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/31 "2002-11-13T20:51:49Z")
> [@](#): > > \*Originally posted by JS Princeton \* > \*\*Neutron stars radiate in the radio. That’s what a pulsar is. \*\* So, by this can I assume (with the understanding of the dangers ass/u/me [mostly me] entails) that a naked Neutron Star would look black in appearance to my unaided eye? Maybe applying a color is wrong (although I’d be interested to know that too) I mean more that it won’t illuminate anything for my mortal eyes to perceive. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 9:00pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/32 "2002-11-13T21:00:06Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\* > > So, by this can I assume (with the understanding of the dangers ass/u/me [mostly me] entails) that a naked Neutron Star would look black in appearance to my unaided eye? Maybe applying a color is wrong (although I’d be interested to know that too) I mean more that it won’t illuminate anything for my mortal eyes to perceive. \*\* I would assume that if it radiate in radio, that if it is hot enough it can also radiate in the visible spectrum as well. I would also think that it was at least plausible that it may display a color in the light reflected/scattered by it… or look like a mirror? ---
**Author:** ![DarrenS](https://avatars.discourse-cdn.com/v4/letter/d/977dab/32.png) [@DarrenS](https://boards.straightdope.com/u/DarrenS)\ **Post date:** [November 13, 2002, 9:38pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/33 "2002-11-13T21:38:42Z")
According to [this](http://oposite.stsci.edu/pubinfo/PR/2000/35/pr.html) link, at least some Neutron stars aren’t totally black: > [@](#): > > this is the closest and brightest of the few known isolated neutron stars Indeed, the fact that Hubble spotted it visually implies that the start is radiating at least some light in the visible spectrum. Also this is interesting. > [@](#): > > The object is very faint (26th magnitude or about 20 billion times fainter than the bright star Vega), and has a blue color. ---
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [November 13, 2002, 10:10pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/34 "2002-11-13T22:10:35Z")
> [@](#): > > \*Originally posted by DarrenS \* > \*\*Indeed, the fact that Hubble spotted it visually implies that the start is radiating at least some light in the visible spectrum. \*\* Neutron Stars have material on their surface (degenerate matter I guess) that hasn’t become neutronium yet. This stuff I would expect to be able to emit light. As previously mentioned though this surface layer is likely _very_ thin so there isn’t much to emit light even if what is there does so vigorously. My question was more on what you’d see if there were no outer, non-neutronium layer. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 13, 2002, 10:27pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/35 "2002-11-13T22:27:51Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\* > > Neutron Stars have material on their surface (degenerate matter I guess) that hasn’t become neutronium yet. This stuff I would expect to be able to emit light. As previously mentioned though this surface layer is likely _very_ thin so there isn’t much to emit light even if what is there does so vigorously. My question was more on what you’d see if there were no outer, non-neutronium layer. \*\* I would expect several feet at least of (probably pretty dense) normal matter on the surface. But you made the same point I was gonna, we were in a thought experiement concerning a “naked” neutron star, so the data wasn’t strictly relevant. ---
**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\ **Post date:** [November 13, 2002, 11:59pm UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/36 "2002-11-13T23:59:10Z")
> [@](#): > > \*Originally posted by scotth \* > \*\* Really? Does [the neutron quadrupole moment] arise from the charge of it’s (the newtron) constituent parts becoming visible (to other particles) at very close range? > \*\* The short answer is yes. The details of baryon structure are still a field of research. The current models, AFAIK, don’t agree with the observations very well, but that’s the basic idea. ---
**Author:** ![Omphaloskeptic](https://avatars.discourse-cdn.com/v4/letter/o/bcef8e/32.png) [@Omphaloskeptic](https://boards.straightdope.com/u/Omphaloskeptic)\ **Post date:** [November 14, 2002, 12:07am UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/37 "2002-11-14T00:07:41Z")
> [@](#): > > \*Originally posted by Whack-a-Mole \* > \*\*My question was more on what you’d see if there were no outer, non-neutronium layer. \*\* I would expect (though I don’t really know) that neutronium, like a normal material, has lots of modes above its ground state (like vibrational modes, etc.) that will be excited (in a thermal spectrum) if the neutronium is hot enough. I don’t see any reason that there shouldn’t be some decay modes with photoemission between some of these states, which is basically what thermal radiation is. Is there any reason this shouldn’t happen? ---
**Author:** ![SPOOFE](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SPOOFE](https://boards.straightdope.com/u/SPOOFE)\ **Post date:** [November 14, 2002, 12:13am UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/38 "2002-11-14T00:13:34Z")
> [@](#): > > As the neutron star increases in diameter it is increasing in mass. Hmm… actually, I came across a [cite](http://www.astronomynotes.com/evolutn/s10.htm) a while ago - when studying neutronium for a debate - that said that degenerate matter - the stuff in White Dwarves and neutron stars - will decrease in diameter as it increases in mass. What’s the real deal? ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 14, 2002, 1:04am UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/39 "2002-11-14T01:04:49Z")
> [@](#): > > \*Originally posted by Omphaloskeptic \* > \*\* > > I would expect (though I don’t really know) that neutronium, like a normal material, has lots of modes above its ground state (like vibrational modes, etc.) that will be excited (in a thermal spectrum) if the neutronium is hot enough. I don’t see any reason that there shouldn’t be some decay modes with photoemission between some of these states, which is basically what thermal radiation is. Is there any reason this shouldn’t happen? \*\* I was unaware that nuclear particles had “states”. Electrons adopt states by being in different “orbits” around the nucleus. I don’t know what is going on exactly with neutronium, but it would appear to me that most of what I know about normal matter wouldn’t apply. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [November 14, 2002, 1:14am UTC](https://boards.straightdope.com/t/neutron-star-question-again/136384/40 "2002-11-14T01:14:28Z")
> [@](#): > > \*Originally posted by SPOOFE \* > \*\* > Hmm… actually, I came across a [cite](http://www.astronomynotes.com/evolutn/s10.htm) a while ago - when studying neutronium for a debate - that said that degenerate matter - the stuff in White Dwarves and neutron stars - will decrease in diameter as it increases in mass. What’s the real deal? \*\* Looking at the link: Degenerate matter and neutronium are not the same thing. Degenerate is just highly compressed matter, atom still maintain their own identities. Neutronium is a ball of neutrons. There should be zero empty space left in neutronium (or near zero). It really can’t compress any more unless you actually start crushing the neutrons. Granted, I could be wrong… (clearly, I am at the limit and over the limit of my knowledge of physics at this point) But, it was my deduction that: 1. neutronium is nearly uniform in density. 2. If density is staying the same, adding mass will add size. 3. If we know an upper mass limit before neutronium will collapse into something else entirely (black hole or some other exotic entity) 4. we would also know the maximum diameter of a neutron star. [Previous page](https://boards.straightdope.com/t/neutron-star-question-again/136384.md?page=1) [Next page](https://boards.straightdope.com/t/neutron-star-question-again/136384.md?page=3)