Aug 16, Science World Report: Stars and black holes can form from rotating matter. Yet exactly how they form has long remained one of the big questions of astrophysics. Now, scientists have discovered magnetic fields can cause turbulences within “dead zones,” helping them understand just how compact objects form in the cosmos.
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 giant cloud of gas. The gravitational pull of this gas concentrated particles at its center, culminating in the formation of a large disk, known as an accretion disc.
Yet while these accretion discs are stable, magnetic fields are capable of prompting turbulences within them. Known as magneto rotational instability (MRI), this phenomenon has the potential to help ensure mass is transported toward the center and angular momentum toward the periphery of the disc. Yet for the MRI to actually work, 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.
Now, scientists may have a new explanation for MRI. It turns out that the helical MRI very much applies to the Keplerian rotation profile if only the circular magnetic field is produced not entirely from the outside but at least partly from within the accretion disc.
“This is in fact a much more realistic scenario,” explained Oleg Kirillov and Frank Stefani, two of the researchers, in a news release. “In the extreme case that there does not exist a vertical field, we’re looking at a problem of what came first–the chicken or the egg. A circular magnetic field acts to destabilize the disc and the resulting turbulence generations components of vertical magnetic fields. They in turn reproduce the circular magnetic field because of the special form of the disc’s rotational movement.”
In other words, the researchers found that MRI is possible even in areas of low conductivity like “dead zones.” The findings are huge for the study of astrophysics since scientists didn’t believe that this was possible
The findings are published in the journal Physical Review Letters.
Source: Cosmic Turbulences in ‘Dead Zones’ Cause Black Holes and Stars to Form, Catherine Griffin, Science World Report