Do Black holes have magnetic fields?

[newtonian]

Do Black holes have magnetic fields?<br /><br />If not, why not?<br /><br />If so, how do they vary and why?<br /><br />Magnetic fields would be caused by internal motion, I assume.<br /><br />Notably rotation rate.

 

[billslugg]

The Black Hole No Hair Theorem here says that a black hole can only have the properties of mass, angular momentum and charge. That would seem to preclude a magnetic field. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[derekmcd]

Good question.<br /><br />It would make sense than a non-rotating black hole would not have a magnetic field. However, I would have to assume that a rotating blackhole does.<br /><br />The magnetic field wouldn't be produces from within the blackhole itself, but rather from the accretion disk surrounding it. Even if the blackhole hole has exhausted its surrounding, then frame dragging of space-time alone would create a magnetic field. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[newtonian]

billslugg - Is said theorem proven?<br /><br />Why wouldn't a black hole have a magnetic field? <br /><br />If it can have charge, then any motion of charged mass should produce a magnetic field - shouldn't it?<br /><br />Is there any observational evidence one way or the other?

 

[newtonian]

derekmcd - Thank you.<br /><br />As above - do we have any observational evidence one way or the other?<br /><br />For example - could black hole jets be influenced by such a magnetic field?<br /><br />What is frame dragging of space-time?<br /><br />Also, I would not assume a magnetic field could not emanate from inside the event horizon - does gravity stop magnetism?<br /><br />Certainly gravity comes from the mass of the black hole itself, not simply the mass at the event horizon - though I have heard a weird theory that indicates the gravity does emenate from the event horizon!

 

[alokmohan]

Good question.

 

[CalliArcale]

<blockquote><font class="small">In reply to:</font><hr /><p>What is frame dragging of space-time? <p><hr /></p></p></blockquote><br /><br />*nervously dipping a toe into a subject out of my depth*<br /><br />As I understand it (trans.: what survived from my brother's attempts to explain it to me), it's a consequence of relativity -- that massive objects warp spacetime, and as they rotate, even drag it around with them.<br /><br />Frame-dragging has been experimentally demonstrated, incidentally. The GPS system has to make a mathematic correction to account for the affect, or those fancy-schmancy navigation systems wouldn't work (because the satellite's actual frame of reference is a bit off from what you'd otherwise expect).<br /><br />I don't entirely understand this, so if you want a better explanation, hopefully one of more physics-minded posters will provide one. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>

 

[derekmcd]

<i>"As above - do we have any observational evidence one way or the other?"</i><br /><br />Yes we do see the effect of magnetic fields around black holes. The tough question is how they are produced.<br /><br /><i>"For example - could black hole jets be influenced by such a magnetic field?</i><br /><br />These jets are quite likely a direct consequence of magnetic fields. Similar to how our magnetic field 'guides' solar winds around the earth, a black hole's magnetic field, which is wound up so tightly, guides infalling matter along the filed to 2 points creating enough energy to shoot the jets outward.<br /><br /><i>What is frame dragging of space-time?</i><br /><br />Imagine yourself elevated above the geographic north pole beyond any atmospheric drag. Frame dragging of space-time will make you spin. See Gravity Probe B.<br /><br /><i>"Also, I would not assume a magnetic field could not emanate from inside the event horizon - does gravity stop magnetism?"</i><br /><br />Considering a magnetic field is produced by motion of electric charge which require charged particles... (we know what happens to particles beyond the event horizon) I'd have to say gravity does, indeed, stop magnetism.<br /> <br /><i>"Certainly gravity comes from the mass of the black hole itself, not simply the mass at the event horizon - though I have heard a weird theory that indicates the gravity does emenate from the event horizon!"</i><br /><br />I believe I have read the same theory. About how from an outsiders relative perspective, all infalling matter is forever 'stuck' at the event horizon... therefore, gravitons are produced at the event horizon. Something to that effect, theoretically. <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>

 

[alokmohan]

I am even more confused .Black hole has no hair ,sorry.

 

[nexium]

I agree, that the accreation disk will produce at least a weak magnetic field. We may never know about magnetic fields inside the event horizon, nor weather the magnetic field can penetrate the event horizon. I'm also of the opinion that all black holes rotate with respect to something, and that only differential rotation (or other phenomena) inside the event horizon can produce a magnetic field. Neil

 

[alokmohan]

But black hole has no hair.

 

[newtonian]

alokmohan - Sounds like a joke!<br /><br />Seriously, I assume you are referring to BillSlug's link. <br /><br />I asked - and it was not answered - has this theorem been proven? <br /><br />I might add that absence of statement does not prove absence - i.e. just because the theorem does not mentiono magnetic fields of black holes does not mean the theorem is against the existence of said magnetic fields.

 

[newtonian]

stevehw33 - Thank you.<br /><br />Of course, had I received formal training after graduating high school (class of '64) - much of what I learned would be out of date anyway. <br /><br />In progressive scientific fields, like astronomy, physics, genetics, medicine, etc., one must keep up with new data and tenable hypotheses in harmony with said data.<br /><br />Formal training is good, of course. But each person must decide what their primary field will be - since time is limited.<br /><br />My primary field is learning and living Bible standards - and Romans 1:20 encourages scientific research to learn about God's qualities and this, plus my natural scientific curiousity, has motivated me to learn here.<br /><br />And I have learned much - but with learning in any field questions also arise, which is why this is my favorite section of SDC.<br /><br />I might add that your posts have also improved lately, and you deserve commendation.

 

[newtonian]

stevehw33 - Thank you for that link. <br /><br />To quote an excerpt:<br /><br />"As the schematic shows, gaseous matter pulled from a normal star forms a disk around the black hole. The gas is heated to temperatures of millions of degrees, and intense electromagnetic forces in the disk can expel jets of high-energy particles."<br /><br />OK, so the electromagnetic fields are in the disk. Sp black hole disks do exert strong electromagnetic forces.<br /><br />This reminds me of our sun's corona which is very hot and which heat is caused by magnetic fields which, in turn, are caused by magnetic dynamoes which float from deep withing the sun to the surface.<br /><br />I doubt that there are magnetic fields floating from near the black hole core to the event horizon - but that is a question.<br /><br />Could there be differential rotation within the event horizon?<br /><br />I have many more questions - see my new thread on today's Science channel program on supermassive black holes.

 

[billslugg]

Newtonian<br />Sorry for the delay. I only remember hearing years ago that black holes had only three quantities. Mass, charge and spin. I found that website but cannot vouch for its authenticity. Apparently Weisstein works for Wolfram, who lists a Doctorate in Physics from CalTech. I would posit that the web site is legitimate and the theorum is generally accepted, but I really do not know. My knowledge of Physics is limited to a couple of undergraduate level courses taken in the early '70's. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[newtonian]

billslugg - no problem on delay in responding. I also get too busy sometimes to respond - and sometimes delay way longer than you!<br /><br />Well, charge implies charged particles, as in ions. Spin implies motion. Motion of ions will produce magentic fields - am I correct?<br /><br />Or does one need differential motion, as in differential rotation of portions of the mass of the black hole.<br /><br />I would expect the latter would exist, especially close to feeding stages for the specific black hole being researched. <br /><br />See my thread on the Science channel broadcast - but one point noted there is that supermassive black holes may have caused galaxies - and many galaxies do not have much diffential rotation - i.e. not from all directions especially in galaxies like Milky Way and Andromeda.<br /><br />However, mergers of black holes and galaxies should produce differential revolution-rotation effects.<br /><br />Please excuse my mixing up revolution and rotation - its just that feeding on revolving stars, gas, etc., should produce rotation effects on the mass of the black hole both at the event horizon and also within the event horizon.

 

[newtonian]

Calli - Thank you for the help.<br /><br />I wonder if that effect may be in part responsible for the strange and beautiful shapes of various nebulae - e.g. the hourglass nebuale,. the antenae nebulae, etc.- in those intriguing Hubble photos?<br /><br />Of course, magnetic fields and shock waves and other causes would mix for a concerto effect.<br /><br />On the GPS corrections due to frame dragging - I had not heard of that unless it is connected with the time change due to relativistic effects due to differential speed.<br /><br />Is this a separate effect from time dilation?<br /><br />Do you have a link on this?

 

[nexium]

My guess is the theorum has not been proved rigoressly, that magnetic fields inside the event horizon can escape, that the acreation disk produces a magnetic field and that all black holes rotate, both inside and outside the event horizon. There may however be some black holes with very little matter in the accreation disk. Neil

 

[alokmohan]

How they get the magntic field for black hole without charge?