# Magnetic Celestial Bodies in Orbit

What would be the effect of large magnetic celestial bodies orbiting each other?

Could a star have enough metallic content to become magnetic?

What would the effect be on magnetic planets in orbit around it?

If that's not possible, how about if a magnetic planet had a magentic moon?

If your answer is that the magnetic pull wouldn't be powerful enough to do anything, take the example of two magnetars in a really tight orbit.

Assuming the result might have something to do with electricity, what effect would this have on the habitability any planets/moons involved? Could it be harnessed somehow?

• Magnetars have a tendency to rip apart atoms. I don't think you could have a binary system of them. – Frostfyre Jul 31 '15 at 15:13
• Also, magnets either attract or repel each other, so your system would probably either collapse in on itself or fly apart pretty quickly. – Frostfyre Jul 31 '15 at 15:14
• So I guess you could only really have two objects that are tidally locked and are attracted to each other? Or maybe they repel each other but are so big that gravity overpowers that? – Varrick Jul 31 '15 at 15:17
• You might be able to get away with a system of objects that are so perfectly balanced that their magnetic repulsion and gravitic attraction cancel each other out. The moment you introduce anything into the system, however, it would fall apart. I'll let one of the experts around here on astrophysics/magnetism work it out. – Frostfyre Jul 31 '15 at 15:28
• A star does not requires metal to generate magnetic field, the internal pressure literally strips the electrons from the hot gas creating large amount of plasmas (ionized gas) and moving charges will... – user6760 Aug 1 '15 at 0:38

Stars already have a very strong magnetic field, metal content won't help on that front as they are made up from plasma rather than solid matter anyway.

The average strength of the magnetic field of the sun is around twice that of earth, however at certain points it can be as much as 8000 times as strong and it actually extends out as far as Pluto!

For the magnetic field between the planets, you can expect it to stabilize so that the two are attracting each other, in other words the magnetic north of one planet will be near the magnetic south of the other.

They will then act as an attractive force and effectively make gravity stronger between the two worlds, this means they will orbit faster and closer together than gravity alone would allow.

The magnetic and rotational north poles may not be at the same location, but it is likely that they would be in this case as that is the only way that the forces would all balance out smoothly. In other words both worlds would rotate around the same central axis, the magnetic and rotational poles would be aligned and the magnetic north and south poles would also be facing in the same direction. The worlds would be orbiting each other faster than normally expected due to gravity alone.

• Regarding the last paragraph, in stars, typically the magnetic poles are aligned with the rotational axes (in most cases). – HDE 226868 Aug 3 '15 at 14:09
• Good answer, thanks for the insights. So I guess no electricity involved then? I was picturing some sort of cosmic dynamo :P – Varrick Aug 3 '15 at 17:17
• In rocky planets magnetism is generated in the molten core so there is no electricity involved on the surface of the planet. – Tim B Aug 3 '15 at 18:00

Interesting models have been made of T Tauri stars, pre-main sequence stars that can have strong magnetic fields (though clearly not as strong as those of magnetars). Data is given in Johns-Krull (2007). The effects of this magnetic field on interactions between the star and its surrounding disk were modeled in (among others) Kuker et al. (2003). Angular momentum is transferred between the star and the disk. The torque generated by the magnetic field on the star is $$T=2\pi r^2 \int_0^\pi (\mathbf{t\cdot r})\sin \theta d\theta$$ where $\mathbf{t}$ is $$\mathbf{t}=\frac{r\sin\theta B_{\phi}}{4\pi}\mathbf{B}$$ and $\mathbf{\cdot}$ denotes the dot product (vectors are represented in $\mathbf{bold}$ type). The authors primarily use spherical coordinates.

In this model, angular momentum is transferred from the star to the disk. However, in a situation with one or more orbiting bodies, there remains the possibility that some angular momentum could be transferred to one or more of the bodies, thereby changing its orbit.