picture of the day archive
The Ant Nebula. Middle: Electromagnetically pinched aluminium can.
Right: "Pinching" water
stream. Image Credits: (Left) R. Sahai (JPL) et al., Hubble Heritage
Team, ESA, NASA. (Middle)
Bert Hickman, Stoneridge Engineering,
www.teslamania.com. (Right) Ian Tresman.
Simple experiments can
demonstrate the principle of the z-pinch that electrical
theorists say is the best explanation of the hourglass shape
of many bipolar nebulas.
As a jet of water flows, the surface tension causes the
stream to constrict, and the jet forms beads or droplets
(see image top right). You can sometimes see this occur, for
example, in the stream of water from a garden hose or
Chief Researcher at the Kurchatov Institute, Boris Trubnikov,
noted that water beading is a good analogy of the plasma
jets that are observed to pinch in the laboratory and the
cosmic plasma in nebulae, too. In plasma, the pinching is
due to the self-generated magnetic field compressing the jet
unevenly along its length. The pinch is sometime called a
z-pinch because the magnetic field lies along the z-axis,
and the beading is sometimes referred to as the sausage
instability because of the shape.
In 1905 James Arthur Pollock and Samuel Barraclough at the
University of Sydney suggested that the distortions in a
length of copper piping used as a lightning conductor were
due to the pinch effect. The phenomenon has also been
suggested as the cause of pinching in bead lightning.
The pinching of metal can be simulated in the laboratory by
simply placing an aluminium soda pop can in a conducting
coil of wire and sending a short pulse of high current
through the coil. The magnetic field generated may be strong
enough to crush the can, in this case producing a
characteristic hourglass shape (see image top, middle).
Pinches in plasmas were first investigated by Willard
Harrison Bennett in the 1930s. He was able to work out a
relationship between the plasma density and current (the
so-called Bennett relation), and pinches are sometimes
called a Bennett pinch.
As cells of cosmic plasma move relative to each other, they
generate currents and magnetic fields that cause them to
produce jets that pinch and bead.
It is perhaps no coincidence that when astronomer Walter
Baade first distinguished individual stars in the Andromeda
Galaxy, he described them as like "beads on a string". And
the Ant Nebula (see image top left), which glows like a
plasma-filled fluorescent light tube, has a characteristic
hourglass pinch in its middle..
With 99% of the universe consisting of plasma, we cannot
afford to ignore the obvious electrical influences any
Submitted by Ian Tresman
David Talbott, Wallace Thornhill
Steve Smith, Mel Acheson
CONTRIBUTING EDITORS: Michael Armstrong, Dwardu Cardona,
C.J. Ransom, Don Scott, Rens van der Sluijs, Ian Tresman
WEBMASTER: Brian Talbott
Copyright 2007: thunderbolts.info