19 X-ray Emission

CHAPTER 19

X-ray Emission

As we saw in the preceding pages, some of the products of the supernova explosion reach their maximum speeds in the range between one and two units, intermediate speeds in our terminology. Inasmuch as these objects continue losing energy to the environment, they ultimately return to the region of three-dimensional space, below the unit speed level, where they are observed as white dwarf stars. The general nature of the evolutionary development of the white dwarfs was discussed in the earlier chapters. At this time we will review the situation from the standpoint of the changes in the radiation pattern that take place as the stars move through their successive evolutionary stages.

The radiation during Stage 1, the immediate post-ejection stage, as we have seen, is at radio frequencies. As explained in Chapter 18, it results from the isotopic readjustments required to bring some of the components of the star back into the zone of stability, after they have been left outside that zone by the decrease in the magnetic ionization level that follows the expansion of the stellar aggregate into time.

It was established in Volume II that the earth is at the one-unit magnetic ionization level. As we found earlier in the present volume, the solar system is somewhere near the average age of the stars in the galactic arms. We may therefore conclude that unit magnetic ionization is normal in the outer regions of the Galaxy. This means that, in the local environment, only one downward step is usually involved in the decrease of the magnetic ionization level on entry into the intermediate speed range. In view of the expansion into a second scalar dimension that occurs at unit speed, it then follows that the series of changes, which ultimately result in the production of radio radiation, are initiated immediately after crossing the unit speed boundary. The isotopic adjustments that arc necessary are therefore substantially complete by the end of the outward travel of the white dwarfs. Consequently. there is little or no radio emission from these objects during the unobservable stage of the return (Stage 2), or during the time that they are observable as stable stars (Stage 3). Furthermore, there is a substantial amount of accretion of low speed matter in this latter stage. facilitated by the fact that the white dwarf remains spatially stationary in the debris left by the supernova explosion. During stage 3, the observable radiation from the white dwarfs comes mainly from the low speed matter.

Evolutionary Stage 4, which follows, involves a return to the speed range below unity. This reverses the process that took place when the unit speed level was exceeded in the outward stage of the travel of these stars. The volumetric change accompanying the drop into the lower speed range increases the neutrino concentration. This restores the unit magnetic ionization level, which raises the zone of isotopic stability, and leaves some of the existing isotopes below the limits of the zone. A series of isotopic adjustments then follows, accompanied by radioactivity. Since these processes take place after the speed drops below the unit level, the radiation is in the x-ray range. The Stage 4 white dwarfs, the cataclysmic variables, are therefore x-ray emitters. “Almost every CV looked at with Einstein [the orbiting observatory] was an emitter of x-rays.”211 (Mason and Cordova)

Here, then, we have a simple x-ray production process that is a direct result of changes that take place during the normal evolution of the white dwarf stars, and does not require the existence of any special or unusual conditions. This contrasts sharply with the production mechanisms postulated in current astronomical thought, as described in this statement from a report of a symposium on x-ray astronomy:

Most of the known, realistic, mechanisms for the generation of x-rays lead to somewhat complicated theoretical statements, and the number of adjustable parameters is often too great for comfort.212

Since all outgoing explosion products that attain upper range speeds emit radio radiation, while only part of them return to the lower speed range and emit x-rays, the total radio emission is much greater than the total radiation at x-ray frequencies. It is also more easily observed, as a large part of the radiation at radio frequencies penetrates the earth’s atmosphere, and can be observed at the surface, whereas the x-ray radiation is almost completely blocked, and can be observed only by instruments that are lifted above the greater part of the atmosphere. But the objects that emit x-rays are moving at speeds below unity, and are optically visible, while most of the radio-emitting objects within the Galaxy are invisible. For this reason, the new x-ray branch of astronomy has accumulated a substantial amount of information about the x-ray emitters and their properties, in spite of the observational difficulties.

One of the important results of this addition to the body of astronomical knowledge has been a significant increase in the volume of evidence supporting the evolutionary pattern of the white dwarf stars that has been derived from the theory of the universe of motion. According to that theory, the white dwarfs originate in supernova explosions, are accelerated to speeds in excess of the speed of light, move outward in time to a limiting distance, then reverse their course, and move back to their original positions and to speeds below the unit level. These stars undergo certain processes on the outward trip, and are then subjected to the same processes in reverse during the return. The finding that the processes leading to the emission of x-rays are the inverse of the corresponding processes that result in the emission of radio radiation establishes a specific relationship of a fixed character between the various features of the x-ray emitters and those of the radio emitters. This means that the nature and properties of the x-ray emitters are strictly defined theoretically. The fact that all of the observational evidence is consistent with the rigid theoretical requirements is therefore an impressive confirmation of the whole interlocking structure of white dwarf theory.

From this theory we find that the x-ray emitters of the type that we are now considering are components of binary, or multiple, systems in which they are associated with stars that originate from the low speed supernova products as infrared stars, and pass through a giant or supergiant stage as they move toward gravitational equilibrium on the main sequence. Thus far, only about 20 percent of the x-ray emitters that have been identified as stars are definitely known to have companions, and the theoretical conclusion that they are all components of binary or multiple systems has been confirmed only to that extent, but there is no evidence to indicate that the remainder do not have companions. Indeed, one of the prominent investigators in this field, R. Giacconi, reports that the evidence from observation warrants “a working hypothesis that all galactic x-ray sources are either members of a binary system or supernova remnants.”213

The theoretical identification of one class of x-ray emitters as white dwarfs is also in agreement with the observational finding that the x-rays “must originate from relatively small, compact objects.”214 This description is applicable troth to the stars currently recognized as white dwarfs and to the stars not currently included in the white dwarf class, but theoretically identified as Stage 4 white dwarfs: the novae and other cataclysmic variables.

Another observable characteristic of the discrete x-ray emitters in the Galaxy is their distribution. Inasmuch as the observable white dwarfs are distributed somewhat uniformly among the stars in the disk of the Galaxy. as the theory requires, it is to be expected that the discrete x-ray emitters will share this distribution. The observations are in full agreement with this expectation. The correlation between the distribution of the planetary nebulae (early Stage 3 white dwarfs), which are more observable than the ordinary white dwarf stars, with the discrete x-ray sources (Stage 4 white dwarfs) is particularly close.215

According to a 1977 report, seven of the approximately 130 observable globular clusters are probable locations of known x-ray sources.216 This is consistent with the conclusion that we derive from theory; that is, the only products of supernova explosions that exist in objects as young as the globular clusters are those produced from the relatively small number of old stars that have been incorporated into the young aggregates.

The observations support the theoretical finding that the x-ray emission from the white dwarfs occurs mainly during Stage 4 of the evolution of these objects, the cataclysmic variable stage. A number of papers concerning the x-ray emission from these variables were presented at a recent symposium. As one participant observed, reports of such observations are now “appearing in profusion.” Both soft and hard x-rays have been detected from the cataclysmic variables, according to another of the investigators, who concedes that “production of hard x-rays, as detected in several of these sources, is hard to understand.”216 The appearance of x-rays in some of the objects of this class and not in others has also been regarded as anomalous.

Both of the seeming anomalies are readily explained by the theory discussed in these pages. The cataclysmic variables are in the last stage of the life of the stars as white dwarfs. Some of them naturally make faster progress toward completion of the transition process than others. Thus some are still emitting hard x-rays, while others have eliminated the hard x-ray sources, the short-lived isotopes, and are emitting soft x-rays. Furthermore, both the character and the magnitude of the emission are subject to variation because of the intermittent nature of the explosive activity. During the explosive outburst, which exposes some of the material from the interior, where the radiation originates, the emission is at a maximum, and the x-rays are “hard”; that is, their frequency is relatively high. Between these outbursts, the radiation is reduced, both in quantity and in frequency, by absorption and re-radiation during its travel through the outer shell of the star.

From the explanation of the nature of the ejections from the cataclysmic variables in Chapter 13 it is evident that those ejections which are accompanied by relatively strong x-ray emissions are nearly continuous in two groups of these objects: the smaller ones, and the older ones, those that are nearing the end of the eruptive stage. It follows that there are continuous, as well as intermittent, x-ray emitters among the Stage 4 white dwarfs. By the time these stars reach the main sequence, the isotopic adjustments are well along toward completion. and the remaining x-ray radiation is reduced to lower frequencies on the way out from the stellar interior, without further explosive activity.

We now turn to the other class of discrete galactic x-ray emitters. the pulsars. As we saw in Chapter 17, the distinguishing characteristic of the pulsars is that they are traveling at ultra high speed in the explosion dimension. Ordinarily these stars increase their net speed as the gravitational force is gradually attenuated by distance, and they eventually disappear into the cosmic sector. But there are influences other than gravitation that tend to reduce the pulsar speed, particularly the resistance due to the presence of other matter in the path of movement. In some instances, where the original explosion speed is only slightly above the two-unit level, the retardation due to these causes may be sufficient to prevent the net speed from reaching two units. And even if the pulsar does enter the speed range above two units, where there is no longer any gravitational restraint on a material object, the pulsar is still subject to the other influences of the material sector. Under appropriate conditions, therefore, the net speed of the outgoing pulsars may reach a maximum somewhere in the vicinity of the two-unit level, decreasing thereafter, and eventually dropping back to levels below unity. A small proportion of the pulsars thus return to the material status rather than escaping into the cosmic sector, as most pulsars do.

Since the linear outward motion of the pulsar is in a dimension of space, the transition at the two-unit level carries it into the region of motion in time. Those pulsars that return, after crossing the two-unit boundary, resume motion in space. The isotopic adjustments that follow this change are therefore accompanied by radiation at x-ray frequencies. On this return trip the pulsars pass through the same pulsation zone that they traversed in the opposite direction in their outgoing stage, and in so doing they emit pulsed x-rays in the same manner in which they emitted pulsed radio radiation on the outward course. By the time the pulsar has passed through the pulsation zone it has had time to complete the adjustments involving the short-lived isotopes which produce the hard x-rays, and the x-rays from “most of the persistent sources that do not pulse” are relatively soft.217 Eventually the incoming pulsars revert to the status of normal white dwarfs, and follow the regular white dwarf evolutionary pattern, including a resumption of x-ray emission in Stage 4 of that evolution.

The pulsating x-ray emitters have some features that are quite different from those of the radio pulsars, and those differences have aroused a great deal of speculation, much of which is little more than fantasy. It is among the complex x-ray emitters, pulsating and non-pulsating, that the theorists are finding candidates for designation as black holes. The explanation of the x-ray emitting objects that we derived from the theory of the universe of motion requires none of these Imaginative constructions. As can be seen from what has been said in the foregoing paragraphs, all that is necessary to explain the x-ray emission and its pulsation is to invert the theory already developed for the radio-emitting objects. The expansion into time during the outward travel of the pulsar lowers the zone of isotopic stability, and initiates isotopic adjustments. On the return trip there is a contraction which raises the zone of stability back to the original level, and causes a reversal of the changes in the isotopes. The adjustments during the outward travel take place while the speeds of the pulsar components are above unity. The fractional residues of the adjustment process are therefore units of speed, which are ejected in the form of radiation at radio frequencies. The adjustments during the return take place while the component speeds are below unity. Here the fractional units are units of energy, and they are ejected in the form of x-ray radiation. The x-ray process is simply the inverse of the radio process.

According to the observers’ reports, the incoming pulsars are concentrated toward the galactic center, as would be expected in view of our finding that this is where most pulsars originate. Since, as we have seen, the pulsars that are produced in these central regions of the Galaxy are moving rapidly outward to a limiting position in space during their radio pulsation stage, it follows that any of these objects which return as x-ray emitters will move down from this limiting position to their original locations as gravitation again becomes effective. The following is a comment by Shklovsky about one of the most conspicuous of the incoming pulsars:

The radial velocity of HZ Herculis, close to 60 km/s, is directed toward the galactic plane. The reason could be that the star has already reached its maximum distance from the galactic plane and is now moving back down.218

In considering the effects of these motions of the pulsars, it is essential to recognize that the motions being observed are taking place in a second scalar dimension of space. As explained earlier, such motion is represented in the reference system only under some special conditions, and it has no effect on the spatial relationships in the original scalar dimension. Thus the association between the low speed and ultra high speed products of the Type II supernova is maintained in essentially the same manner as the association between the white dwarf product of the Type I supernova and its low speed companion that we examined in the earlier chapters. In the early stages, the low speed companion of the pulsar is merely an expanding cloud of dust and gas, and it is doubtful if the life period of an outgoing pulsar is long enough to enable this cloud to contract into an observable object. (One such case has been reported, but this identification needs to be investigated further).

The incoming pulsars are, of course, much older, and their low speed companions have developed to the point where they are observable. The x-ray emitters are therefore recognizable as binary systems. The pulsars most likely to fall just short of reaching the point of no return are those produced by explosions of very large stars. These are products of rapid accretion, and a large proportion of their total mass is below the destructive ionization limit at the time of the explosion, because of the amount of time required for equalization of the ionization levels. This results in an explosion speed near the lower limit of the ultra high range, and increases the probability that the outward motion will be halted. When one of these pulsars returns to the speed range in which it is observable as an x-ray emitter, its large low temperature component is seen to be a giant or supergiant. A 1975 report states that 5 of the 8 then known binary x-ray stars incorporate massive supergiants (relatively rare in the Galaxy).219

The white dwarf product of the explosion of a massive star is also a large object of its class. In Cygnus X-1 the x-ray star is estimated to be in the range from 6 to 10 solar masses, while the optical star is twice as large. This object is currently the favored candidate for the black hole status, on the ground that the accepted theories limit both the white dwarfs and the hypothetical neutron stars to smaller masses. Shklovsky, whose estimates of the masses of the components of Cygnus X-1 are quoted above, follows these figures with the comment, “so it would follow that the Cygnus X-l source is a black hole.”220

Here one can see how little substance there is to the structure of reasoning on which the case for the existence of black holes is based. Certain observed entities that have all the properties of the class of objects called white dwarf stars are excluded from this classification on the strength of a wholly unsupported theoretical conclusion that the white dwarfs are subject to a mass limit in the neighborhood of two solar masses. Then these objects that are observationally indistinguishable from white dwarfs, but are above the hypothetical mass limit, are arbitrarily assumed to have some different type of structure. Finally, a structure, the black hole, is invented for these objects on an ad hoc basis.

When the black hole concept was first proposed, it was recognized in its true colors. As expressed in one comment published in 1973, only the “counsel of desperation” leads to invoking this hypothesis.221 This situation has not changed. The black hole hypothesis has no more foundation today than it had ten years ago when that judgment was passed. But the intangible nature of the hypothesis, which prevents testing its validity, and its constant repetition in the astronomical literature, together with the general retreat from strict scientific standards in recent years, has resulted in a quite general, although somewhat uneasy, acceptance of the black hole. There is now an increasing tendency to call upon this purely hypothetical concept for the solution of all sorts of difficult astronomical problems.

In reaching the conclusion that the compact astronomical objects in the stellar size range are all white dwarfs differing only in properties related to their speeds, this present work is not in conflict with any observed facts; it is merely challenging some unfettered flights of the imagination. In this connection, it should be noted particularly that the assumption that gravitation is effective within the atom is the cornerstone of all of the currently accepted theories of the various compact astronomical objects. There is no evidence whatever to support this assumption. Observation tells us only that gravitation acts between atoms. The assumption that it also plays a role within the atom rests entirely on a theory of atomic structure that, as brought out in the preceding pages of this and the previous volumes, is contradicted by many definitely established physical facts, and is kept alive only by invoking the aid of a whole series of ad hoc assumptions to evade the contradictions.

There are some special conditions under which it is theoretically possible for outgoing pulsars to emit pulsed x-rays. As noted earlier, those pulsars that originate in locations where the gravitational retardation is minimal have relatively low spatial speeds, and remain near the location of the supernova explosion for a considerable period of time. While the entire aggregate of ultra high speed explosion products maintains its identity in time, and all of its components move at the same explosion speed, so that their pulsations are synchronized, some portions of the whole are entrained in the material moving outward in space, in the same manner as the local aggregates of intermediate speed matter discussed in Chapter 15. Since these spatially detached portions of the pulsar are in close contact with the low speed matter, interaction with that matter reduces the speeds of some of the constituent particles below the unit level, causing isotopic adjustments and emission of x-rays. Similar interactions take place at the surface of the main body of the pulsar, particularly where, as in the Crab Nebula, the pulsar still remains in the midst of the debris at the site of the supernova explosion.

The strong x-ray emission from the Crab Nebula pulsar is not duplicated in the Vela pulsar, the second of these objects located in a supernova remnant. It appears that the slow-moving explosion products, which are still dense around the 900-year old Crab pulsar, have been largely dispersed in the 10,000 years since the Vela pulsar was produced. This conclusion is consistent with the difference in the polarization of the radio radiation, which is relatively low (about 25 percent222) in the radiation from the Crab Nebula and pulsar, but almost complete in that from the Vela pulsar.223

As noted in Chapter 16, it is currently believed that the energy radiated by the Crab Nebula is generated by the central star, the pulsar, and is transferred to the nebula, where the radiation is presumed to be produced by the synchrotron process. We have seen that the arguments in favor of the synchrotron hypothesis depend mainly on the “there is no other way” contention, and cannot stand up under critical scrutiny. The hypothetical energy transfer mechanism is likewise without any firm support. The astronomers admit that “the mechanisms for the transport of the pulsar power through the nebula and for the acceleration of the electrons are not well understood.”217 “Not well understood” is, of course, the currently fashionable euphemism for ”unknown.”

Earlier we found that the energy which powers the radio radiation from the supernova remnants is not a product of the explosion, but is generated by radioactive processes in aggregates of intermediate speed matter that have been entrained in the outgoing low speed explosion products. From the points brought out in the preceding paragraphs it can now be seen that the x-ray radiation from the remnants originates in a similar manner; that is, from spatially separated portions of the pulsar. But the x-ray radiation is only a minor component of the total radiation from an outgoing pulsar, and it therefore terminates relatively soon. Consequently, the pulsed x-ray emission of this nature is limited to very young supernova remnants of the Crab Nebula type. This nebula itself is the only known instance at present (1983). The emission from the young remnant Cassiopeia A is not pulsed, because, as we saw earlier, the maximum speed of the explosion products that constitute this remnant was never great enough to carry them to the pulsation zone.

Any x-ray radiation from outgoing pulsars should be accompanied by strong radio emission, and pulsed x-rays without any more than a weak radio accompaniment can usually be regarded as originating in incoming pulsars. However, the most distinctive characteristic of each class of pulsar is the direction of the change in the period. The periods of the outgoing pulsars are increasing. Those of the incoming pulsars are decreasing. Most of the decreasing periods are longer than those of the outgoing pulsars, and because the return motion is subject to a variety of environmental conditions, they do not conform to the kind of a regular pattern that we find in the periods of the outgoing pulsars.

Inasmuch as the pulsar moves outward in the explosion dimension as a unit, irrespective of the spatial locations of its components, and the pulsation rates are determined by the speed, these rates are the same for all types of emission. Otherwise, the characteristics of the pulses produced by the different processes can be expected to differ. They may be out of phase, the relative intensity of the pulses may vary, or x-ray emission may cease while radio emission is taking place, or vice versa. A number of such dissimilarities are reported to be present in the radiation from the Vela pulsar.

The “x-ray stars” are relatively rare. Only about 100 are known to exist in the Galaxy, about 20 of which are pulsating,217 and it is believed that the observed number is almost complete. This is consistent with the conclusion that the pulsars that fail to reach the conversion level at unit speed are mainly those originating in explosions of very large stars, which are likewise rare outside the unobservable central regions of the galaxy. Actually, none of the classes of discrete x-ray sources thus far considered is observable in large numbers. R. Giacconi points out that the compact x-ray sources are either “exceedingly rare or represent short-lived x-ray emitting phases in stellar evolution.”224 The increase in the number of weak emitters of soft x-rays detected in recent years modifies the observational situation to some extent, but the conclusion is still valid. The theoretical identification of the soft x-rays with age, and the evidence from the remnants that ages from 25,000 to 50,000 years are sufficient to reduce the emission to the soft status, show that Giacconi’s second alternative is the correct one.

In the case of the x-ray stars, the returning pulsars, the time that was spent above the two-unit speed level was too short for any large amount of isotopic adjustment to have taken place, and the reversal of the changes that did occur is accomplished relatively rapidly. The isotopic composition of the ordinary white dwarfs is fully adjusted to the intermediate speed during the outward travel of these objects, and the reverse adjustment continues over a long period of time, but here the strong radiation is intermittent. It escapes from the star in major quantities only under special circumstances of short duration. Smaller amounts are emitted as leakages or in minor outbursts.

The supernova remnants provide an opportunity for observing the evolution of the x-ray emission. The more distant an isotope is from the center of the zone of stability, the more energetic its radiation, and the shorter its half-life, generally speaking. Consequently, the original hard, or energetic, x-rays from matter dropping back into the low speed range are followed by softer emissions as time goes on and the short-lived isotopes are eliminated. The initial x-ray radiation from the remnants is identical with that from the hard compact sources. For instance, the x-rays from Cassiopeia A are reported to be “quite hard.”225 The radiation then continues on a soft basis for a relatively long period of time. For example, the x-rays from the Cygnus Loop, one of the older remnants, are all in the soft range, below 1 KeV.226

Because of the variety of sources and conditions involved in the observed emission of x-rays, it is possible to establish some limitations on the x-ray production process that can be compared with the theoretical deductions. First, we can conclude that it is extremely unlikely that two different processes for production of strong x-ray radiation would be put into operation by the same supernova event. The mechanism by which the x-rays are produced must therefore be one that is applicable to both of the observed types of supernova products: compact sources and extended remnants. (It is generally conceded that the supernova, which produces a compact x-ray emitter also, leaves a remnant). This imposes some severe constraints on the kind of a process that can be given consideration.

Furthermore, when the observed emission of x-rays from the remnants of supernovae is considered in conjunction with the results of observations that have sought. but tailed to detect. high frequency radiation in significant amounts from the supernovae,227 a still more rigid requirement is imposed on x-ray theory. The fact that the emission occurs both from concentrations of matter (hot spots) and from diffuse clouds (extended sources) in the remnants means that the emission must result from the condition of the matter itself, not from the way in which that matter is aggregated. But the absence of x-ray radiation during the observable stage of the supernova explosion, when the particle energies are at a maximum, shows that the thermal processes are not, in themselves. adequate to account for the strong x-ray emission.

In the remnants. the x-rays come from matter that has been losing energy for a considerable period of time, more than 50,000 years in some cases, and is now at an energy level well below the peak reached in the explosion. The observations thus require the existence of a process in which matter that loses a portion of its energy after having reached the high energy level of a violent explosion undergoes some kind of a change that involves emission of x-rays. In the preceding pages we have seen that the development of the theory of the universe of motion leads to just such a process.

All of this development of theory had taken place long before the astronomical x-ray emitters were discovered. It had already been determined that the fast-moving products of stellar and galactic explosions undergo inverse radioactivity on crossing from the low speed to the upper speed ranges, and thereby produce radiation at radio frequencies. It had also been found, from theoretical considerations, that certain of these explosion products acquire sufficient speed to escape from the material sector into the cosmic sector, whereas others do not attain the escape speed, and eventually return to the relatively low speeds that are normal in the material sector. All that was required in order to complete the theoretical understanding of the x-ray emitters was a recognition of the rather obvious fact that the process previously deduced as the source of the radiation at radio frequencies from the outgoing products of stellar and galactic explosions also works in reverse to produce x-rays and gamma rays from those of the explosion products that return to the low speed range.

We thus have a theoretical definition of the origin and properties of the x-ray emitters that has not been constructed to fit the observations, in the manner in which most scientific theories are devised, but had already been deduced from the postulates that define the universe of motion, and had been published prior to the discovery of the astronomical x-ray emission The close agreement between this pre-existing theory and the observational information now available is thus highly significant. Two features of this explanation of the x-ray emission are especially noteworthy. First, the theoretical x-ray process is an essential element of the theoretical energy production process. Hence it is not necessary to provide a separate explanation of how the energy is produced. Second, the same process is applicable to all of the strong x-ray emitters.

Meanwhile, conventional astronomical theory is faced with the problem of having to put together a new combination of energy generation and radiation production processes for almost every new type of x-ray emitter that is encountered. Current thinking in this area is centered largely on the situation in the Crab Nebula. Here the astronomers have been able to construct a theory with which they are reasonably comfortable, although, as indicated earlier, they are somewhat uneasy about their inability to identify the mechanism by which the energy transfer required by their theory is carried out. In this theory the central pulsar is a rotating neutron star, which releases energy by slowing its rotation. This energy is transferred to the nebula, which then radiates “by means of the synchrotron process, emitting radio waves, visible light, and X-rays.”226 But few of the radiation sources conform to this pattern. Aside from these few, the radio emitting pulsars have no associated remnants, and the supernova remnants contain no pulsars. Some different hypotheses are therefore required to account for the radio emission from these sources. The x-ray emitters complicate the situation still further. Rotation is ruled out as a source of energy for these objects, as only a few of them exhibit the pulsation that is interpreted as evidence of rotation, and in these few the pulsation periods are decreasing. Giacconi points out that, because of this speed-up, “energy could not come from rotation,” and he goes on to say:

The only remaining plausible source of the energy was gravitational energy released by accretion of material from the companion star onto the x-ray emitting object.228

Here, once again, we meet the ubiquitous “no other way” argument. There is no physical evidence to support the assumption that such a process is actually in operation. Whether or not this is “plausible,” it is simply a hypothesis based on a set of assumptions about the nature of the two components of the x-ray emitting binary system, assumptions that, as we have shown, are invalid.

Neither the synchrotron process nor the accretion process is applicable to the remnants, other than those of the Crab Nebula type, so still another x-ray emission process has to be devised for them. Here the assumption is that “the high energy radiation is generated by heating as the gas of the remnant collides with the interstellar medium.”229 Two big problems confront this hypothesis: (1) it is hard pressed to account for the existence of “hot spots” in the interiors of many remnants, particularly where, as in Cassiopeia A, the hot spots are quasi-stationary, and (2) the energy emission from the remnants decreases much more slowly than this explanation predicts.

The x-ray emission as a whole is another example of the way in which present-day astronomical theory arrives at many different explanations of the same thing. In view of the incomplete nature of astronomical knowledge as it now exists, in spite of the remarkable progress that has been made in the past few decades, it is not possible to test these hypotheses against established facts. In the absence of the disproof that would follow from such a test, each of these explanations has a degree of plausibility, when considered individually, although all are based almost entirely on assumptions. But like the many different theories devised to account for the individual manifestations of extremely high density that were enumerated in Chapter 17, the multiplicity of explanations of the same phenomenon has the cumulative effect of exposing the artificiality of the foundations of the hypotheses. The demonstrated need to devise a new explanation of a phenomenon whenever it is encountered in new setting is prima facie evidence that there is something wrong with the current understanding of this phenomenon.

As might be expected, extra-galactic observations add still further dimensions to the problem. All galaxies emit some x-rays. In many cases, this radiation evidently originates from sources similar to those that are observed in our own Milky Way galaxy. Both discrete sources and x-ray emitting supernova remnants have been identified in some of the other galaxies that are close enough to be within the range of available observational facilities. Among the more distant galaxies there are some much more powerful x-ray emitters. The Seyfert galaxies, a class of very active spirals that will be discussed in Chapter 27, are observed to be strong x-ray sources. Galaxies that show evidence of violent activity, such as M 82 and NGC 5128 also radiate enormous amounts of x-ray energy. Quasars are likewise prodigious emitters of x-rays, as would be expected from the turbulent conditions in these objects, which are undergoing rapid and drastic changes.

Another recent finding that has attracted a great deal of attention is the discovery of x-rays in the intergalactic space in some distant clusters of galaxies. A 1980 report by Giacconi identifies two classes of these emissions one in which the emitting sources are “clumped around individual galaxies or groups of galaxies” and another in which the emission is “concentrated near the center and falls off smoothly with distance.”228 According to Gorenstein and Tucker, the x-ray emission comes from clusters with “a centrally located supergiant elliptical [spheroidal] galaxy.”167 These authors also report that M 87, the nearest galaxy of the giant class, and a member of the Virgo cluster, “is enveloped by an x-ray emitting cloud nearly a million light years across.”

The x-ray emission in these clusters of galaxies is currently attributed to the presence of a hot gas. “The space within such clusters is pervaded by gas heated to some 10 million degrees,228 asserts Giacconi. It is evident that this situation calls for some more critical consideration. In the light of what is known about the fundamentals of heat and temperature, a high temperature in a medium as sparse as that of intergalactic space is impossible. As explained in Volume II, the temperature of a gas is the result of containment. The pressure is a measure of the containment, while the temperature is a measure of the energy imparted to the gas that is subject to pressure. Thus the temperature, T is a function of the pressure, P. For a given volume, V, of ”ideal gas,” the two quantities are directly proportional. as indicated by the general gas law, PV = RT, where R is the gas constant. If the pressure is very low, as in the near vacuum of intergalactic or interstellar space, the temperature is likewise very low. It is measured in degrees, not in millions of degrees.

It is often asserted that portions of the gas in the vicinity of hot stars or active galaxies are “heated by radiation.” But radiation does not repeal the gas laws. Absorption of radiation does not increase the temperature if the gas is free to expand. The radiation may ionize the atoms of the gas, and there appears to be an Impression that this elevates the temperature, but this conclusion is incorrect. The degree of ionization is an indication of the intensity of the ionizing agency, whatever it may happen to he. At very high temperatures thermal ionization takes place; that is, a part of the thermal motion is converted to the type of motion known as ionization In this case the degree of ionization is actually an indication of the temperature. the intensity of the thermal motion. But ionization by another agency, such as radiation, is independent of the temperature. Motion in the form of radiation is converted directly to motion in the form of ionization. Here the degree of ionization is an indication of the intensity of the radiation, and has no relation to the temperature. The possibility of a radiative addition to the gas temperature must therefore be ruled out. The x-rays in the space around the giant galaxies cannot be thermally produced. A non-thermal process at the locations where they are observed must generate them.

In the universe of motion the x-ray emission is due to leakage of intermediate speed matter from the high pressure region in the interiors of the giant galaxies. Where the temperature of the leaking matter is in the lower section of the intermediate speed range, a relatively small amount of cooling carries some of the particles across the unit speed boundary and into the lower speed range. In this case the emission begins shortly after the leaking matter leaves the galaxy, and the emission “falls off smoothly with the distance” as in Giacconi’s second category, and around M 87. A higher initial temperature delays the start of the x-ray radiation, and favors emission in the vicinity of the other galaxies of the cluster, where the matter escaping from the giant is cooled by contact with the outlying matter of those galaxies. The distribution of the x-ray emissions then follows the “clumpy” description in Giacconi’s first category. As we will see in Chapter 27, the Seyfert galaxies are also losing intermediate speed material from their interiors, and the x-ray emission from these objects, while considerably stronger, for reasons that will be explained in the subsequent discussion, is a result of essentially the same process that is operating around the distant giants.

These conclusions with respect to the origin of the x-rays that are observed in the vicinity of the giant galaxies are also applicable, on a smaller scale, to the production of x-rays in the surroundings of individual stars. These x-rays are believed to originate in the stellar coronas, and it has therefore been concluded that “temperatures of a million to 10 million degrees”228 exist in these coronas. Here, again, the existence of such temperatures is excluded by basic thermal principles. Consequently, the x-rays cannot be produced thermally in these locations. But, as in the galactic situation, the x-ray production is easily explained on the basis of leakage of intermediate speed matter from the interiors of the stars, followed by a return to the low speed range in the coronas.

This “leakage” explanation also accounts for the relative emission rates from the different classes of stars, one of the areas in which the new observational findings are upsetting previous theories. “The predictions of x-ray emission based on classical theories says Giacconi, ”fail completely to account for the observations.”228 As can be seen from the description of the stellar energy generation process in the earlier pages, the central regions of all stars are in the condition where the combined thermal and ionization energies are just sufficient to begin imparting intermediate speeds to a considerable number of particles. In view of this near uniformity of the internal situation, the principal determinant of the amount of leakage, aside from the mass of the star, is the thickness of the layer of matter through which the intermediate speed particles have to make their way. It follows that the leakage rate should be relatively greater in the smaller stars. This is confirmed by the Einstein observatory results, which show that the ratio of x-ray to optical emission is 100,000 times as large in the small main sequence stars of spectral class M than in the sun, a member of the larger class G. These results, says Giacconi “will force a major reconstruction of theories of both stellar atmospheres and stellar evolution.”228

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