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Astronomers Solve Magnetic Fields Mystery
An anonymous reader writes "It is a long-standing and unsolved mystery why 80% of all planetary nebulae are not spherical. Theories suggest that magnetic fields play a role in shaping planetary nebulae. A team of astronomers from Germany has now discovered the first direct clue that magnetic fields might indeed create these remarkable shapes. Planetary nebulae are expanding gas shells that are ejected by Sun-like stars at the end of their lifetimes."
I have to say it's nice to see magnetic fields getting more praise than usual! All my professors tell me is "magnetic fields aren't important and blah blah blah so don't worry or care about them" ... then again I'm currently majoring in Electrical Engineering. :)
It will be great to see what else unfolds in terms of the importance magnetic fields play in the structure of the universe!
Now then, Dmitri, you know how we've always talked about the possibility of something going wrong with the Bomb...
The crab is a supernova remnant, not a planetary nebula.
Whatever would iron have to do with this? This is about plasma movement in a magnetic field. Or did you think star explosions ejected nice, neutral iron atoms? Here's a clue: the magnetic moment of iron is caused by its outer electrons.
It doesn't turn into a single spinning ball because as the constituents collide, they sometimes stick. The more the empty spaces between them grow, the less often they collide. (Collision rate scales as the third power of the mean free path.) In a mature planetary system or galaxy, collisions between major bodies are so rare that they're nearly unheard of.
On a solar system scale, the spin of the central body plays a large role in this, but it is still a kind of a game of chase-the-tail.
When the whole system is still gas, something starts it spinning -- a simple thing like a star passing nearby gives objects (the gas particles) a bit of angular moment, which is thus transferred to the system as a whole over eons of time through collsions, gravity, magnetic forces, etc.
Now, if a LARGE object passed by in the XY plane, and a SMALL object passed by in the YZ plane, you will end up with a spin *mostly* in the XY plane, but the *WHOLE SYSTEM* will balance out with a single plane of spin somewhere in between.
Eventually the smaller objects become larger objects, which collide less, thus distributing the angular moment less efficiently. There may be one central body spinning in the XY plane, but a few of the large objects can have a wildly different orbital plane. But not many objects will HAVE this wildly different orbital plane, because back when the system was being formed, the angular moment transfer WAS very efficient.
Also, 'circular' orbits, like the earths or mars or Jupiters, are fairly rare on a random scale of things; and if you have a bunch of objects orbiting in different planes with highly ellipical orbits, they have a much higher chance of smacking into each other (or some larger object, like jupiter) than the same object would if it were in a more circular orbit which happened to be in a different plane than that of the central masses spin. Don't forget the time scales in question here!
Now, finally, in systems like that of the Earth and its huge moon, you get tidal interactions; while the moon will never shift in its orbit enough to be in an equatorial orbit, it *does* shift more closely to one every day, thanks to the 'gravity drag' between itself and Earth. Really what is happening is that the Earths spin is accelerated in the direction of the moons travel (really, this is slowing our spin rate down, think acceleration in the physics sense). Earth has already done this to the moon; hence the 'tidal lock' which has the moon presenting the same side to Earth at all times.
Were you to watch the Earth moon system forever, eventually what you would see is two bodies rotating about a central point, both with the axis of spin of each body being parallel to the axis of rotation about said central point (hope you can visualise that!). In reality this won't occur in any amount of time, the influence of the sun, and the fact that the moon would actually leave earths gravitation influence before alignment could occur prevent it. (The orbit of the moon gets larger as it steals earths rotational momentum).
That was fun.
a white dwarf according to this page
The remnant in the middle of a planetary nebula is a sphere of incredibly hot solid helium (mostly), which used to be the core of the star (i.e. where the fusion actually took place).
It is called a white dwarf at this stage, and as it has no power source (just residual heat) it eventually cools over an extremely long time to become a black dwarf.
Planetary nebulae are not formed by explosion (well, not violent explosion, anyway). And, yes our Sun will form a planetary nebula some day (billions of years from now). The Sun will eventually become a Red Giant star, true. At the end of its Red Giant phase it will shed its outer envelope, exposing its core. That core is what becomes a White Dwarf. The outer envelope becomes the nebula.
The Sun is not and never will be a Brown Dwarf. A Brown Dwarf is a failed star wanna-be, one that almost (but not quite) started a sustainable nuclear reaction in its core. A Brown Dwarf is not really a star at all. Stars do not become Brown Dwarfs. Stars end up as either White Dwarfs, Neutron Stars, or Black Holes (or some exotic variant of one of those three).
Well, it's partly that, but keep in mind, planetary nebula are very much three-dimensional objects. For example, the Ring Nebula is actually, in all probability, more or a barrel shape like the Butteryfly Nebula. However, because we're seeing it edge-on, we see it as a ring, rather than it's true shape. And the result is color concentration on the edges.
Similarly, some of the perceived complexity in objects like the Ant Nebula may be due to perspective, as we see it from an angle.
And speaking of the Ant Nebula, as is mentioned in the APOD article, another likely contributing factor to nebular complexity is the presence of other bodies orbiting the new white dwarf, such as a companion star or planetary body. These objects likely manipulate the shape of the nebula via gravitational or electromagnetic forces.
The Earth and its moon already do rotate about a common point -- the center-of-mass of the combined system. It's just that given the relative masses of the two bodies, the center of mass is pretty darn close to the center of mass of the Earth.
We can believe in you for 3 minutes, but beyond that, even the King of All Cosmos can't be expected to wait.
Once upon a time there was a telescope operator who was very nervous and when rain clouds threatened Paranal one night her nervousness turned to panic and she could not break from her very long closing script and just close the damn doors no matter the state of the system and hundreds of gallons of rain fell onto the eight meter collecting surface and washed through the central hole in the mirror and down filling the large yellow camera the size of four refrigerators mounted below. That instrument lovingly refered to on Cerror Paranal as The Yellow Submarine is FORS1--the one that intercepted the photons that caused you to read this today.