From this news item
“Lars Bildsten of the University of California at Santa Barbara said the flare is probably related to tangled magnetic fields beneath the surface of the brown dwarf, which seem to be able to generate X-rays.”
How can magnetic fields generate x-rays? Never heard of anyone generating x-rays via magnetic field manipulation or is this related to the strange physics of the brown dwarf surface interactions and beyond our ken at present?
A magnetic field is created by electrons in motion; it’s always created as a field perpendicular to an electric field Isn’t there a right hand rule for this:
Picture electricity in a wire. If you point the thumb of your right hand along the wire, there is a magnetic field “around” the wire curling in the direction of your fingers. This is how an electromagnet works (the coil directs and concentrates all of the field lines of the wire). Anywhere there are energized electrons, there is electromagnetic radiation. X-rays are just EM radiation of a certain wavelength. My guess is that these stars have circulating matter that is of a certain characteristic as to generate a sufficient magentic field, and also which fluoresces or phosphoresces photons in the X-ray energy region. Just a WAG, but an informed one.
I don’t think they mean that magnetic fields create X-rays directly. One way to generate X-rays is to heat something to a few million degrees. I say “something” but at this temperature it becomes a plasma - just a jumble of electrons and nuclei floating around, not neutral atoms. They are flying around at such high speeds that they interact and produce X-rays. Another method is to accelerate particles to a very high energy, and have them hit a target. Electrons accelerated by about 50,000 volts of electric field is usually enough. This is how X-ray generators in hospitals and airports work.
Now, this latest observation from Chandra X-ray Observatory shows a flare, i.e. a brief but itense flash of X-rays. Since the duration and X-ray energies look fairly similar to solar flares, we guess they are more or less the same phenomenon. Solar flares have been studied in detail, and the only possible explanation for them is that they are caused by “magnetic reconnection.” Since it takes energy to create magnetic field, you can say that there is energy stored in a magnetic field. Now if the magnetic field twists to a complicated shape, it has even more energy. If it is strained too much, it will suddenly snap into a simpler shape. The simpler shape field has less energy, so the difference in energy is suddenly released as heat and/or accelerated particles. You can also think of it as two magnetic fields with opposite directions coming together and annihilating each other, releasing energy. Temperatures of over ten million degrees is fairly common, as well as particles accelerated to over 10 MeV (equivalent of an electron accelerated by a 10-million volt electric field).
You can get more information about solar flares (and more importantly, cool images) at:
Yohkoh Public Outreach Program
TRACE homepage
SOHO homepage
These are project homepages for some of the recent solar observation satellites.
A changing magnetic field creates an electric field. A changing electric field creates a magnetic field. So if the magnetic field is changing, and the rate at which it is changing is changing, etc., then it will create a changing electric field, which will create a changing magnetic field, which will create a changing electric, etc. The result is a wave. An electromagnetic wave. X-rays are a type of electromagnetic wave.
This is true, and radio waves are indeed produced on stars this way. But I don’t think you can generate X-rays by shaking macroscopic magnetic fields - the frequency would be way too low. The only practical way of generating such high-energy electromagnetic radiation is by taking a very small charged object and shaking it very fast. An electron makes a good “small charged object.” There are different ways of “shaking” an electron. One can accelerate it to a high energy and collide it with another particle. As I said, this is how X-ray generators usually work. You can also bend the path of a high-energy electron with a strong magnetic field. This is called cyclotron or synchrotron radiation. This happens in particle accelerators which use magnetic fields to force particles to travel in a circle. Some accelerators are built for the sole purpose of producing synchrotron radiation, though more often they use secondhand ones which is no longer powerful enough for cutting-edge particle physics research. Or you can have an electron swing very close to a proton - they attract and change course very fast. This happens spontaneously when you heat up a plasma.
In solar flares, the magnetic field only acts as an energy source for accelerating and/or heating up the plasma. It is not directly involved in X-ray emission.
Thank you to all respondents for clueing me in.
Magnetic field > electrical field > heat > plasma > x-ray
Now… I figure if I can get some of those super powerful rare earth magnets (magnets o’ death) they are always advertising on Ebay I can have a good shot at making some ball lightning.
“Watch this kids!”
“Run! Daddy’s got magnets again!”