Session VII.6
The Extension of Atmospheric to Space Electricity
C. E. R. Bruce <index.htm>
[in /Problems of Atmospheric and Space Electricity/, 1963, ed. Coronti,
S. C.]
Electrical Research Association, Leatherhead (Great Britain)
Introduction
During his Kelvin Lecture on "The Sun" to the Institution of Electrical
Engineers in May, 1941, CHAPMAN (1941) referred to a solar prominence
which reached a height of 1,000,000 km in an hour. A little mental
arithmetic established that its velocity of propagation must have been
almost exactly that of a lightning leader stroke and that, since it
moved "like lightning", it probably was lightning of some form.
The 22 years of research on atmospheric astrophysics since then have
convinced me that not only this solar prominence, but also the universe
is, so to speak, all-electric, and that electric fields and their
breakdown in electrical discharges account for the observed phenomena
and accelerate the process of universal evolution from universe to
galaxies, from galaxies to stars, from stars to planets and, possibly,
from large planets to satellites. In short, atmospheric astrophysics is
merely an extension of atmospheric electricity.
There are good grounds for believing that the conditions necessary for
the generation of these electric fields exist in cosmic atmospheres
(BRUCE, 1955).
However, even if the exact nature of the process remains undetermined,
as that in the earth's atmosphere has done for over 200 years, so that
it is merely a hypothesis, it is the hypothesis to end cosmic
hypotheses. These last are, at present, almost legion. They include the
existences of magnetic fields, relativistic electrons (in atmospheres
otherwise known to be at about absolute zero!), gas jets (to account for
magnetic storms, etc.), processes of aggregation (to account for the
galactic spiral arms), solar nuclear explosions, collisions between
galaxies, collisions between matter and anti-matter, explosions in stars
which detonate explosions in other stars, gravitational implosions, etc.
The last four are only some of the suggestions put forward to account
for cosmic radio sources alone, which, as we shall see, are accounted
for in some detail by the discharge theory.
Atmospheric Electric Field Building
Two papers presented to the last Conference in 1958 (BRUCE, 1959a)
echoed Franklin's statement in 1755, that he had no solution to offer to
the problem of thundercloud electrification. I have suggested that the
process involved in the terrestrial and cosmic atmospheres may be
"static" electrification of dust or grains (BRUCE, 1955). In the
long-period variable stars, for example, the additional dust formed in
their atmospheres at light minimum is sufficient to dim the star's light
by factors of ten or more. The atmospheric temperatures are therefore
quite low, so that electric fields can evidently be built up to
breakdown and can account for the bright emission lines which begin to
appear in their spectra towards light minimum; i.e., the probability of
the occurrence of the phenomenon evidently increases as the temperature
decreases and as the amount of dust increases. Similarly, in galactic
atmospheres, the ratio of grains to gas molecules is a million times the
ratio of even the Aitken nuclei to gas molecules in the earth's
atmosphere (ALLEN, 1963), and their temperatures are 0-100°K so that
again there would appear to be every reason for electrification of the
grains to occur, albeit very slowly. The time available is, however,
long, on the order of 10^10 years. In the largest galaxies, the field
has still not had time to build up to the breakdown value, and no
discharge channels, or spiral arms, are observed in them. The smallest
of galaxies, on the other hand, as the theory predicts, are found to
contain the most highly developed arms of types Sc and SBc (Fig. 1). It
will be seen that the theory thus provides a categorical argument
against continuous creation (BRUCE, 1961a).
Hubble himself wrote that there is evidence of the occurrence of some
cataclysmic action at SO (HUBBLE, 1936). The theory provides this in the
form of electrical discharges at 500,000,000°K which propagate with a
velocity of 2500 miles/sec for a period of 10-100 million years (BRUCE,
1958a)! If you can imagine anything more cataclysmic than that...!
Hubble's sequence of nebular types
*Fig. 1. The sequence of nebular types.*
There is room for much work on such subjects as the formation and
electrification of grains in the terrestrial, stellar and galactic
atmospheres. The existence of times to breakdown of 10^2 sec, 10^7 ,
sec, 10^9 -10^10 years or more in these three conditions will allow
checks of any theories. I have already essayed a very rough comparison
between the former two periods (BRUCE, 1955). Information regarding the
nature of the grains in galactic atmospheres is afforded by the
polarization of starlight which they cause, which shows that they are
needle-shaped and orientated in one direction in one region, as they
would be by an electric field. Thus it should be possible to calculate
the magnitude of the field.
Relation between current and field strength
*Fig. 2. The relation between current and field strength. At /a/ all
free electrons are swept out; at /b/ the field strength is sufficient to
lead to ionization by collision*.
It is argued that galactic atmospheres, for example, are infinitely
conducting, and that the electric fields therein are impossible. One
eminent professor of mathematics claimed to be able to demonstrate this
in five minutes by setting up and solving the wrong equations. At about
0°K, we have a perfectly insulating atmosphere with grains which can
become charged and apply a field to the gas. The process will be exactly
analogous to the build up to and onset of the Townsend mechanism in air
at atmospheric pressure. If there are any free electrons formed, then
they will be swept out by the field to one of the grain electrodes. The
current will increase as the field increases, until all the free
electrons are swept out (at a, Fig. 2). After this point, it will remain
constant, until the field increases sufficiently to lead to ionization
by collision (at b, Fig. 2). In. a galactic atmosphere with 1 atom or
molecule per cm^3 ; this will presumably be when the electric field
reaches a value of about 10^-14 V/cm. In the extensive stellar
atmospheres of planetary-system dimensions of the long-period variables,
with pressures of about 10^-6 atmosphere, the breakdown fields will be
about 10^-2 V/cm.
Breakdown in Electrical Discharges
The evidence for these cosmic electrical discharges is the same as that
which would be afforded by terrestrial atmospheric discharges to an
observer outside the earth, i.e., the sudden appearance of bright
emission lines in its spectrum. In the essentially molecular band
spectra of the long-period variable stars, for example, superimposed on
a continum at 1500-4000°K, there begin to appear, towards minimum light,
bright emission lines of hydrogen and neutral helium, indicating
temperatures of 5000-10,000°K. In some associated stars, like AX Persei,
the level of excitation rises until lines of FeX are observed.
Similarly, there are many galaxies which show patches of bright
emission, and we shall see that their spectra indicate the existence of
discharge temperatures of about 500,000,000°K in an atmosphere which is
normally quoted as being at 0-100°K! If there is any way of bringing
about these conditions apart from an electrical discharge, then
engineers and nuclear physicists would be very interested to hear of it.
In addition, there is the whole subject of radio astronomy, which may
almost be regarded as a prediction of the electrical discharge theory
which I failed to make.
Cosmic Gas Thermometers
There are two "thermometers" which can be used in estimating the
temperatures of electrical discharges, whether laboratory, atmospheric,
or cosmic. The first derives from an effect, the existence of which was
probably first emphasized by BELLASCHI (1937). The pressure in the axial
regions of an electrical discharge is increased by an amount
proportional to the product of the current and the current density, as a
result of the movement of the conducting particles in the discharge's
own magnetic field. In an electric arc, the current density increases at
and towards the electrode spots. Therefore, pressure gradients are set
up which give rise to the anode and cathode jets (MAECKER, 1955). Their
velocity will be that of sound in the gas; if it can be determined, we
will have a measure of the temperature. Applied to the lightning
discharge, the theory explains the existence of metallic lines in the
spectrum of the discharge up to heights of 2m above the ground (BRUCE.,
1958b), and applied to the welding arc by my colleague King, it explains
the physical basis of arc welding (KING, 1959).
*Table I*
Temperature Measurements of Electrical Discharges in the Atmospheres of
Three Stars^(1)
*Star* *Level of
excitation (eV) * *Temperature
(°K)* *Gas velocity
(km/sec)* *Temperature
(°K)*
*X Cygni* *Fe I, FeII
(8-10)* * 9,000* *12* *10,000*
*P Cygni* *CIII, NIII
47* *47,000* *28* *47,000*
*AX Persei* *CaXV
814* * 814,000* *110* *814,000*
(1) After BRUCE' 1962a, b.
The second thermometer derives from an observed relationship between the
level of excitation and the discharge temperature, which was first
brought to my notice for the laboratory arc by King. If the level of
excitation observed is /k/ eV, then the discharge temperature is k.10^3
eV. These thermometers will be referred to as the "/v/-thermometer" and
"I.P.-thermometer" respectively. Table I shows their application to
discharges in the atmospheres of three stars (BRUCE, 1962a; for a fuller
discussion, see BRUCE, 1962b). The application of the I.P.-thermometer
to laboratory discharges has recently been extended to lines of Si XIII
or about 2500 eV (BRUCE, 1963c), while the /v/-thermometer predicted the
existence of an upper limit to cosmic gas velocities of about 5000
km/sec (BRUCE, 1958a), the existence of which has been commented on by
astrophysicists. The reason for the upper limit is not hydro-dynamical
as one enquirer asked (BRUCE, 1962a), but thermonuclear. The temperature
of these discharges is limited by the onset of thermonuclear processes
at about 500,000,000°K.
Applied to solar discharges, the theory is the only one which has
explained the solar streams (BRUCE, 1961b, 1963a), which have been
postulated as the cause of magnetic storms since about 1896. The theory
led to the conclusion that temperatures of well over a hundred million
degrees must be reached in these outbursts (BRUCE, 1959b, c), a
deduction which was confirmed by U.S. Navy Satellite observations
(BRUCE, 1960a).
Another prediction concerned the Evershed effect. In 1909, Evershed
observed an outflow of gas from sunspots at 1-2 km/sec, and only these
velocities had been confirmed by subsequent investigation, whereas the
/v/-thermometer suggested that they should reach 8 km/sec, the velocity
of sound in ionized atomic hydrogen at 6000°K, the temperature of the
photospheric arc discharges (BRUCE, 1963b). The observation of these
predicted higher gas velocities by his colleague, Bumba, was announced
by Severny at a recent I.A.U. Symposium (no. 12) on cosmic gas dynamics
(SEVERNY, 1961).
Velocity of Propagation of Electrical Discharges
The propagation of voltage breakdown is proportional to the product of
the breakdown field and the mean free path. The former is proportional
and the latter inversely proportional to the gas density so the velocity
of propagation of cosmic electrical discharges should be the same as
that of lightning discharges, namely about 3.10^7 cm/sec. The
atmospheres of the long-period variables extend about 10^14 -10^15 cm
above their surfaces, so the duration of the discharges should be about
(10^14 ~ 10^15 /(3.10^7 ) or about 10^7 sec. This agrees reasonably well
with the periods during which bright emission lines appear in their spectra.
However, as the temperature of the leader stroke increases, as it
apparently and understandably does when there is a fairly steep density
gradient, then there will come a point when the velocity of sound, and
therefore the velocity of the jet of hot gas generated by the discharge,
exceeds the velocity of voltage breakdown. The jet of hot gas then takes
over the propagation process, and velocities of propagation up to about
4000 km/sec become possible. These higher velocities are reached at the
temperatures observed in solar atmospheric discharges, and explained how
the time lag between the solar flare and the resulting magnetic storms
can be as low as one day. Protons have actually been observed entering
the earth's upper atmosphere at velocities of up to 3500 km/sec during
aurorae.
Cosmic Static and Radio Sources
Early in these researches, I suggested (BRUCE, 1949) that certain
effects observed in the earth's magnetic field may be the "static"
radiated from discharges in the sun's atmosphere. The currents, 10^14 A,
and current densities, 10^-5 -10^-3 , A/cm^2 , required to account for a
disturbance in the earth's field rising to 40[gamma] in 15 min seemed
reasonable. Further work on these lines might prove of interest.
It is of interest that a flare-star has recently been observed to be a
radio source (LOVELL et al., 1963). In these stars, as in the sun, but
not in the long-period variables, the discharges take place in an
atmosphere having a rapid density gradient, in which high temperatures
are built up which probably reach thermonuclear values.
Though most textbooks suggest that cosmic radio noise is the result of
synchrotron radiation of relativistic electrons moving in a magnetic
field, SMITH (1961) has recently pointed out that this theory does not
yield the observed relationship which connects spectral energy
distribution with wavelength. The observed relation lies between those
given by ionization processes and Bremsstrahlung respectively; these two
mechanisms will be active in electrical discharges. So far as existing
theories are concerned, the necessary magnetic fields and relativistic
electrons are mere postulations; there is no mechanism apart from an
electrical discharge which will account for their origin (BRUCE, 1958c).
Globular nebula N.G.C. 4486
*Fig. 3. Globular nebula N.G.C. 4486.*
Photographic enlargement of the central regions of N.G.C. 4486
*Fig. 4. Photographic enlargement of the central regions of N.G.C. 4486.*
It was suggested in the original summary of these researches (BRUCE,
1944) that breakdown of the atmospheric electric field built up in a
globular nebula, like that of N.G.C. 4486 shown in Fig. 3, led to the
formation of the irregular or spiral arms. N.G.C. 4486 is the radio
source, Virgo A, and in order to see what is going on in it, the
photographic enlargement of the central regions shown in Fig. 4 was also
obtained at Mount Wilson and Palomar Observatories. It shows the
discharge in its early stages, a mere 300 parsecs long, as compared with
the average length of tens of kiloparsecs for the spiral arms. This
explains why Burbidge's estimate of the total energy radiated by a
radiogalaxy, derived from observations on this radio source, was only
10^58 ergs (BURBIDGE, 1961), as compared with Heeschen's later value of
10^60 ergs (HEESCHEN, 1962), which agrees with that derived from the
discharge theory (BRUCE, 1961c).
The theoretical value derives from the observed change in the atomic
constitution of the gas effected by its being exposed to thermonuclear
temperatures on the order of 500 million °K for 10-100 million years.
This changes the proportion of heavy atoms in the gas from 0.003, that
of the original gas which went to the formation of the older stars of
Population II, to 0.03, the proportion observed in the younger stars of
Population I, which were later formed from the gas collected along the
spiral arms which had been subjected to the discharge.
The energy liberated during the radio-galaxy phase is therefore the
thermonuclear energy represented by the loss of mass involved of 10^39
gm or 10^60 ergs.
NGC 2371/2 (Gemini or Peanut Nebula)
*NGC 2371/2* NGC 2392 (Eskimo Nebula
*NGC 2392* NGC 3587 (Owl Nebula)
*NGC 3587*
NGC 2452 Nebula
*NGC 2452* NGC 6853 (Dumbell Nebula) (M27)
*NGC 6853* NGC 4361 (Lawn Sprinkler Nebula)
*NGC 4361*
NGC 6058 Nebula
*NGC 6058* NGC 6563 Nebula
*NGC 6563*
NGC 6543 (cat's eye nebula)
*NGC 6543* NGC 6778 Nebula
*NGC 6778*
*
Fig. 5. Photographs of planetary nebulae showing pairs of old discharge
channels.
* Note: The images of nebulae from this original article were too poor
to reproduce, and have been
replaced by alternative images from a variety of sources. The captions
remain unchanged
When the corresponding phenomenon occurs on a stellar atmospheric scale,
the result is a miniature spiral nebula or straight-armed nebula (BRUCE,
1960b, 1961b; Fig. 5), the existence of which was predicted by the
discharge theory. The confirmatory photographic evidence was found in a
paper published 42 years earlier at Lick Observatory (CURTIS, 1918),
thanks to a suggestion from Merrill of Mount Wilson Observatory, one of
the astronomers whose help was sought in the search. It had been
realized that the spectra of stars with pairs of bright emission lines
could be explained if discharges in the two arms caused jets of gas in
opposite directions. The result of a more detailed study of the gas
velocities in two of these nebulae was quoted earlier. These had proved
quite intractable to Campbell and Moore, whose investigations of the gas
velocities were published at the same time as Curtis, photographic
survey (CAMPBELL and MOORE, 1918).
Epilogue
I wrote in my contribution on /Terrestrial and Cosmical Lightning
Discharges/ to the last conference on Atmospheric Electricity (BRUCE,
1958b) that "One purpose of the present paper is to introduce to
meteorological physicists a new field in which the writer thinks that
they may well find the answer to some of their thunderstorm problems,
namely that of cosmic (electric fields and) electrical discharges". It
is gratifying that five years later, a whole section of this conference
is to be devoted to this extension of the subject of atmospheric
electricity which I then proposed.
In the present short talk, it has only been possible to refer to a few
more developments of the theory. Some of the others are, however,
summarized in the accounts circulated (BRUCE 1960c, 1963d) before the
conference, and may come up in the discussion; a forthcoming E.R.A.
Report will give a list of about 75 papers, notes and articles in which
the subject is discussed further.
Summary
The suggestion is that the introduction of a new major variable
(atmospheric electric fields) leads to a correlation of astrophysical
phenomena and a consistent theory of universal evolution, without any
additional ad hoc hypotheses, which are so necessary in astrophysics at
present. The process of electric field building and the evidence for
cosmic electrical discharges, including the whole new subject of radio
astronomy, are referred to, and the writer's two cosmic gas thermometers
discussed. It is shown that the theory offers an explanation of radio
galaxies, and accounts for their occurrence in nebulae of Hubble's Type
SO, and for others of their characteristics. Since the paper was
presented the radio haloes of galaxies and the recently discovered
extremely intense radiosources have been explained in letters to the
/Journal of the Institution of Electrical Engineers/.
References
* Allen, C.W., 1963. /Astrophysical Quantities/. Athlone, London,
291 pp.
* Bellaschi, P. L., 1937. /Elec. Eng./, 56:1256.
* Bruce, C.E.R., 1944. A New Approach in Astrophysics and Cosmogony
<astro.htm>. (Private publication.)
* Bruce, C.E.R., 1949. /Observatory/, 69:110.
* Bruce, C.E.R., 1955. /Phil. Mag/., 46:1123.
* Bruce, C.E.R., 1958a. /E.R.A. Rept/., Z/T 117:7 pp.
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