<p>Strong magnetic fields (say two magnetars) would exert torques that would flip the bodies until they were attracting each other, unless they are spinning rapidly enough to resist this.  However, if the two magnetic bodies are in orbit about a third object (say a black hole) and were close in radius of orbit, then this attraction would add to the orbital <a href="https://arxiv.org/pdf/1803.06704" rel="nofollow noreferrer">instabilities that occur with just gravity when orbits are too near</a> and first discussed <a href="https://www.sciencedirect.com/science/article/pii/S0019103583711693?via%3Dihub" rel="nofollow noreferrer">here</a>.  The details are complicated, but there are exchanges of angular momentum plus perturbations to the eccentricities, so that the orbits become chaotic until they rather randomly end up at a safe distance from each other. One might say they repel each other.</p>
<p>Magnetic exchange of energy and angular momentum is thought to be the dominant mechanism that <a href="https://www.nature.com/articles/441938a" rel="nofollow noreferrer">sends matter rapidly from an accretion disk</a> into a black hole.</p>
<p>However, since magnetic fields fall off quickly and magnetic fields in rocky object are never very strong, the magnetic effects can't be important beyond a few hundred kilometers or so for anything except a magnetar. A rocky object as massive as a moon or planet would not have a magnetic field strong enough to flip the spin of its neighbor or play a big role in their orbital dynamics.</p>

CC BY-SA 4.0
2024-08-16T17:56:27.060Z
You shouldn't reference a comment in your answer - you can repeat the information, it's fine. No need for the shout-out.
Darth Pseudonym
CC BY-SA 4.0
2024-08-16T18:06:09.973Z
@eshaya but then as the inner object moves inward when repelling the outer one it would be crashed onto the planet that they are both orbiting?
vengaq
CC BY-SA 4.0
2024-08-17T04:27:17.573Z
Depends on how much energy it takes to send the outer one to infinity versus how much energy it takes to send the inner one to the surface.
eshaya
CC BY-SA 4.0
2024-08-19T09:30:32.577Z
How can readers (like me) know if this is true or false? Usually with such complicated assertions a Stack Exchange answer will cite authoritative sources, or do the math in the answer itself. Otherwise anybody could post anything and make it sound assertive and logical without necessarily being right. Can you cite some studies that reach these conclusions? *Thanks!*
uhoh
CC BY-SA 4.0
2024-08-19T15:16:57.440Z
"The object with the smaller radial orbit is sped up when behind the outer object and slowed down when ahead. It therefore spends more time ahead, and is therefore slowed down while it speeds up the outer object." Isn't this still true when reversing the smaller and larger radial objects? The larger radial object also slows down when ahead, which leads to the opposite conclusion that it spends more time ahead, slowing down while it speeds up the inner object.
Nuclear Hoagie
CC BY-SA 4.0
2024-08-19T15:53:48.367Z
But, if the outer object slows down when ahead it spends less time there (overtaken more quickly) getting slowed down.  If it speeds up when behind, it spends more time there (better matching the speed of the inner one) being sped up. The outer object speeds up, which pushes it farther outward.
eshaya
CC BY-SA 4.0
2024-08-16T15:28:29.920Z
2024-08-19T21:56:40.750Z
2024-08-19T21:56:40.750Z
eshaya
<p>I was wondering whether an astronomical object (a planet, a star, a neutron star, a magnetar...) with a sufficiently strong magnetic field could repel another object (like a planet, an asteroid...), or at least maintain it in a safe zone avoiding a collision, provided that it had a powerful enough magnetic field. Is this possible?</p>

CC BY-SA 4.0
2024-08-16T13:06:01.327Z
The only way this would work would be, I guess, if you have a highly diamagnetic body approaching a powerful magnetic field, because two inherently magnetic bodies interacting would almost certainly just flip their orientations until they were no longer repelling. So maybe if we imagine a pure bismuth asteroid. I don't think there's any way this would work with just a generic space object because they'd mostly be made of ferromagnetic or paramagnetic materials and thus not repelled by a magnetic field of any strength.
Darth Pseudonym
CC BY-SA 4.0
2024-08-16T13:59:24.140Z
@DarthPseudonym so even in the case of a bsimuth asteroid being repelled by a strong magentic field it would tend to rotate until i gets attracted?
vengaq
CC BY-SA 4.0
2024-08-16T14:24:17.447Z
No, diamagnetic materials always oppose the applied magnetic field regardless of orientation. I'm saying if you had a magnetar and an object with its own magnetic field, like Earth or a gigantic horseshoe magnet, the repelling magnetic fields would probably generate a torque to flip into the correct orientation rather than simply being pushed away.
Darth Pseudonym
<orbital-mechanics><neutron-star><magnetic-field><planetary-science><magnetar>
Can astronomical objects repel other bodies if they have a sufficiently strong magnetic field?
vengaq
# Can astronomical objects repel other bodies if they have a sufficiently strong magnetic field?

(Asked by: username_0 on 2024-08-16)

I was wondering whether an astronomical object (a planet, a star, a neutron star, a magnetar...) with a sufficiently strong magnetic field could repel another object (like a planet, an asteroid...), or at least maintain it in a safe zone avoiding a collision, provided that it had a powerful enough magnetic field. Is this possible?

**Tags:** orbital-mechanics, neutron-star, magnetic-field, planetary-science, magnetar

> **Comments:**
> **username_1**: The only way this would work would be, I guess, if you have a highly diamagnetic body approaching a powerful magnetic field, because two inherently magnetic bodies interacting would almost certainly just flip their orientations until they were no longer repelling. So maybe if we imagine a pure bismuth asteroid. I don't think there's any way this would work with just a generic space object because they'd mostly be made of ferromagnetic or paramagnetic materials and thus not repelled by a magnetic field of any strength.  
> **username_0**: @username_1 so even in the case of a bsimuth asteroid being repelled by a strong magentic field it would tend to rotate until i gets attracted?  
> **username_1**: No, diamagnetic materials always oppose the applied magnetic field regardless of orientation. I'm saying if you had a magnetar and an object with its own magnetic field, like Earth or a gigantic horseshoe magnet, the repelling magnetic fields would probably generate a torque to flip into the correct orientation rather than simply being pushed away.  

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## 1 answers

### Answer by username_2 on 2024-08-16. Score: 0

Strong magnetic fields (say two magnetars) would exert torques that would flip the bodies until they were attracting each other, unless they are spinning rapidly enough to resist this. However, if the two magnetic bodies are in orbit about a third object (say a black hole) and were close in radius of orbit, then this attraction would add to the orbital [instabilities that occur with just gravity when orbits are too near](https://arxiv.org/pdf/1803.06704) and first discussed [here](https://www.sciencedirect.com/science/article/pii/S0019103583711693?via%3Dihub). The details are complicated, but there are exchanges of angular momentum plus perturbations to the eccentricities, so that the orbits become chaotic until they rather randomly end up at a safe distance from each other. One might say they repel each other.

Magnetic exchange of energy and angular momentum is thought to be the dominant mechanism that [sends matter rapidly from an accretion disk](https://www.nature.com/articles/441938a) into a black hole.

However, since magnetic fields fall off quickly and magnetic fields in rocky object are never very strong, the magnetic effects can't be important beyond a few hundred kilometers or so for anything except a magnetar. A rocky object as massive as a moon or planet would not have a magnetic field strong enough to flip the spin of its neighbor or play a big role in their orbital dynamics.

> **Comments:**
> **username_1**: You shouldn't reference a comment in your answer - you can repeat the information, it's fine. No need for the shout-out.  
> **username_0**: @username_2 but then as the inner object moves inward when repelling the outer one it would be crashed onto the planet that they are both orbiting?  
> **username_2**: Depends on how much energy it takes to send the outer one to infinity versus how much energy it takes to send the inner one to the surface.  
> **username_3**: How can readers (like me) know if this is true or false? Usually with such complicated assertions a Stack Exchange answer will cite authoritative sources, or do the math in the answer itself. Otherwise anybody could post anything and make it sound assertive and logical without necessarily being right. Can you cite some studies that reach these conclusions? *Thanks!*  
> **username_4**: "The object with the smaller radial orbit is sped up when behind the outer object and slowed down when ahead. It therefore spends more time ahead, and is therefore slowed down while it speeds up the outer object." Isn't this still true when reversing the smaller and larger radial objects? The larger radial object also slows down when ahead, which leads to the opposite conclusion that it spends more time ahead, slowing down while it speeds up the inner object.  
> **username_2**: But, if the outer object slows down when ahead it spends less time there (overtaken more quickly) getting slowed down.  If it speeds up when behind, it spends more time there (better matching the speed of the inner one) being sped up. The outer object speeds up, which pushes it farther outward.  

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