Just how stars and black holes in the Universe are able to form from rotating matter is one of the big questions of astrophysics.
What we do know is that magnetic fields figure prominently into the picture.
However, our current understanding is that they only work if matter is electrically well conductive—but in rotating discs this isn't always the case.
Now, a new publication by Helmholtz-Zentrum Dresden-Rossendorf physicists in the scientific journal Physical Review Letters shows how magnetic fields can also cause turbulences within "dead zones," thus making an important contribution to our current understanding of just how compact objects form in the cosmos.
When Johannes Kepler first proposed his laws of planetary motion in the early days of the 17th century, he could not have foreseen the central role cosmic magnetic fields would play in planetary system formation.
Today, we know that in the absence of magnetic fields, mass would not be able to concentrate in compact bodies like stars and black holes.
One prominent example is our solar system, which formed 4.6 billion years ago through the collapse of a gigantic cloud of gas, whose gravitational pull concentrated particles in its center, culminating in the formation of a large disc.
 |
| Dr. Frank Stefani |
"To explain the growth rates of stars and black holes, there has to exist a mechanism, which acts to destabilize the rotating disc and which at the same time ensures mass is transported towards the center and angular momentum towards the periphery."
As early as 1959, Evgenij Velikhov conjectured that magnetic fields are capable of prompting turbulences within stable rotating flows.
Although it wasn't until 1991 that astrophysicists Steven Balbus and John Hawley fully grasped the fundamental significance of this magneto rotational instability (MRI) in cosmic structure formation.
Balbus and Hawley will be this year's recipients of the one million Dollar Shaw Prize for astronomy, which will be given in September 2013.
However, to ensure the MRI actually works, the discs have to exhibit a minimum degree of electrical conductivity.
In areas of low conductivity like the "dead zones" of protoplanetary discs or the far-off regions of accretion discs that surround supermassive black holes, the MRI's effect is numerically difficult to comprehend and is thus a matter of dispute.
HZDR scientists, who to date have been mostly concerned with an experimental study of the MRI, have now offered a new theoretical explanation for this phenomenon.
Read the full article here
More information: O.N. Kirillov, F. Stefani: Extending the range of the inductionless magnetorotational instability, in Physical Review Letters 111 (2013), S. 061103, DOI-Link: link.aps.org/doi/10.1103/PhysRevLett.111.061103
Posts
No comments:
Post a Comment