# Magnatars (Hypothetical Question)

1. May 31, 2010

### 1Truthseeker

This is a question for the astronomers and other scientists that have knowledge of magnatars. I am conducting some research for a science fiction novel, and I would like to be somewhat reasonable in my canon. Here is my question:

How many AUs would be the minimum safe distance from a somewhat older magnatar (older, because it has a period of say 8-10 seconds). The hypothetical purpose would be to observe/study its strong magnetic field and perhaps (again, science fiction so don't take this the wrong way) sap its angular momentum through reactive inductance by placing a load on the field.

I realize that this is so out of the ordinary, but it is a hard science fiction novel and I would appreciate any knowledge you could give in regard to this scenario. I realize that the magnetic fields of magnatars are unimaginably strong, so I am figuring it will have to be quite a distance.

Thanks in advance for any that take the time to seriously answer this question.

Humbly,
Ts.

2. May 31, 2010

### stevebd1

Here's wikipedia's page on Magnetars-

http://en.wikipedia.org/wiki/Magnetar" [Broken]

Quote-

Last edited by a moderator: May 4, 2017
3. May 31, 2010

### 1Truthseeker

Thanks for the reply. I had posted here because I felt the Wikipedia article on maganatars did not sufficiently answer my questions or give me a level of assurance. I was hoping to find an authoritative response from an astronomer or cosmologist before I based my entire novel around the concept.

4. May 31, 2010

### nicksauce

I guess for a first approximation, the 3 pieces of information we need are
1) What is the strength of the magnetar's magnetic field at a given distance?
2) How fast does said magnetic field decay?
3) In how strong of a magnetic field can humans in a spaceship survive?

Now I am just doing some guess work: Let's take the magnetar's field to be 10^10 tesla at the magnetar's surface (R = 10km). I think it is reasonable to assume the field is like a dipole, and thus decays as 1/r^3. Finally, we need to do some guesswork as to what magnetic field a spaceship could withstand. This is probably pretty flexible for a sci-fi story though. But let's say it can withstand a magnetic pressure of 1000 atmospheres.

We then want to solve

$$\frac{B^2\left(r/10\textnormal{km}\right)^{-6}}{2\mu_0} = 1000\textnormal{atm}$$

If I do this I get an answer of..... 10^109 metres?!?!?!?... Well clearly I am either calculating wrong or one of my assumptions (most likely the dipole assumption) is wrong. Hopefully someone can add some insight to this post.

5. May 31, 2010

### 1Truthseeker

Thank you for this reply. I have a question: will a strong magnetic field affect non-ferrous materials? For example, if the station were made of some type of material that did not interact with it, would it not then have affect on how deep within the field it was? (Notwithstanding gravity).

Also, are magnetars emissivity in the visual spectrum? Ie: would the depiction that an individual observing it from a safe distance seeing it "pulse" light a light house require viewing in upper bands of EM or would it be a visible dim white like that of neutron stars?

Thank you again, I apologize for these ignorant questions but they are very helpful in making this story seem at least plausible.

6. May 31, 2010

### Nik_2213

Dare we assume the magnetic pole is aligned with the spin axis ? If not, your intrepid explorers not only have the steady field, but a very significant cyclic variation. It would surely induce ferocious eddy currents in a metal hull. Perhaps you need to surround the crew area with a superconductive shell to repel the magnetic field and 'shield' the occupants ?

7. May 31, 2010

### 1Truthseeker

Hmm very interesting insight into that. I had naively assumed it would be aligned with the spin axis. I am thinking that a distance of 0.5 to 1 AUs is a minimum. But I am just guessing. Perhaps I am over thinking this. :)