The Later Cycles
Only a relatively small proportion of the mass of the star needs to be converted into energy in order to produce the Type I supernova explosion. The remainder, constituting the bulk of the original mass, is blown away from the explosion location at high speeds. We therefore find the site of such an explosion surrounded by a cloud of material moving rapidly outward. The prevailing view is that the entire mass is dispersed into interstellar space. As expressed by Shklovsky, The gaseous material expelled during the outburst forever breaks its connection with the exploding star and travels out into interstellar space, interacting with the interstellar medium. 47 In this particular case he is referring specifically to supernovae of Type II, but his subsequent comments make it clear that these remarks apply to Type I as well.
It is evident that a large part of the matter ejected into space is actually dispersed in this manner, but there is likewise a significant part of the total that does not escape. As we will see in Chapter 6, the matter in the central portion of the star does not participate in the expansion into space. Because the speeds generated by the explosion are distributed over a wide range, another substantial portion of the ejected mass is restricted to relatively moderate outward speeds. One factor that has a bearing on this situation is that the Type I explosion takes place in the center of the star rather than throughout the structure. Consequently, much of the ejected material does not come out in the form of finely divided debris, but consists of portions of the outer sections of the star. These are ejected in aggregates of various sizes, what we would call fragments if we were dealing with solid matter. Such quasi-fragments have lower initial velocities than the small particles or individual atoms, since the acceleration imparted by a given pressure decreases as a function of the mass, where the density is uniform. They also expand quickly from their highly compressed initial state, which reduces their temperature drastically and makes them invisible. The visible portions of the Type I supernova remnants are mainly the fastest particles.
During their outward travel, these explosion products are subject to the gravitational effect of the total mass until the fastest components reach the gravitational limit, and to a gradually decreasing effect thereafter. It follows that the slower components are subject to gravitational retardation, as well as to some resistance from the interstellar medium, for a very long period of time. If we take the previously cited figure of 60 solar masses as the size of the exploding star, and assume that a third of the total mass goes into energy, the outer portions of the explosion products are subject to the gravitational effect of 40 solar masses, In Chapter 14 we will develop an equation for calculating the gravitational limit, and from this equation we will find that the gravitational limit of an aggregate of 40 solar masses is 23 light years, or 7 parsecs, The radii of the observed Type I supernova remnants in the Galaxy average about 5 parsecs.48 Thus the expansion of these remnants, great as it has been, has not even taken the fastest of the explosion products beyond the gravitational limit of the aggregate as yet. Clearly, many of the slower products cease moving outward long before they reach the gravitational limit of the remaining mass.
At this stage, where the expansion ceases, there is a cloud of cold and very diffuse material occupying a tremendous expanse of space. But unlike the large dust and gas clouds in the galactic arms, this material is under gravitational control. The gravitational effect of the mass as a whole on each individual particle is small because of the huge distances involved, but a net gravitational force does exist, and once the expansion has ceased, a contraction is initiated. Another long interval must elapse while this initially minute force does its work, but ultimately the constituent particles are pulled back to where the internal temperature of the mass can rise enough to reactivate the energy generation process, and the star is reborn.
This star is now back in area O of the CM diagram, first as an infrared star, and later, as it contracts and increases in temperature, as a red giant. This red giant resembles the first generation of stars of the same type, but it is not identical with them. It has gone around the cycle and through the explosion process, and has undergone some modifications in so doing. The most significant respect in which the new stars of the second cycle differ from their counterparts of the first cycle is that the second cycle star has a gravitationally stable core. The first cycle star condensed from a practically uniform dispersed aggregate. As noted earlier, some of these stars had nuclei on which to build, but only in rare instances is this anything more than a small fragment. Thus, until it reaches the critical density, such a star is simply a contracting dust and gas cloud. On the other hand, the aggregate of matter from which the second cycle star condenses is heavily concentrated towards the center, the site of the supernova explosion. The gravitational contraction therefore proceeds much faster in this central region, and a large part of the mass of the star reaches a state of gravitational equilibrium by the time that the atomic energy process is initiated. The newly formed second cycle star is thus a two-component system, a stable core with a large contracting outer envelope.
In this combination structure, the luminosity is determined by the amount of energy generated. This, in turn, depends on the mass, which is concentrated mainly in the core. But the surface temperature corresponding to a given luminosity depends on the volume of the star, and this is mainly the volume of the envelope. Thus the surface temperature of the early second cycle star is similar to that of an early first cycle star, while the luminosity is similar to that of a main sequence star instead of being concentrated in one region in the upper right of the CM diagram in the manner of the early first cycle stars, the early stars of the second cycle occupy a band along the right of the diagram similar to the upper part of the main sequence on the left. We will designate this type of star as Class C. Adding the number of the cycle, these stars of the second cycle are Class 2C stars.
After the initial movement downward from region O to a position determined by the stellar mass, the evolution of the Class 2C stars, resulting from continuation of the process of condensing the outer envelope, leaves the luminosity practically unchanged, but the surface temperature increases because of the reduction in the size of the radiating surface. This second cycle star thus moves almost horizontally across the CM diagram if it is in a region of minimum accretion. Any further accretion that takes place puts the terminal point, the location at which the star reaches gravitational equilibrium, higher on the diagram. The evolutionary paths of the Class C stars are therefore totally different from those of Class A, the stars of the first cycle.
The Class C pattern is illustrated in Fig.5. The numbers shown with the names of the prominent stars identified in the diagram are the masses in solar units. As can be seen from these values, the mass scale for the Class C stars on the right of the diagram is practically identical with that of the Class B (main sequence) stars on the left. The line XY then represents the evolutionary path of a star of about five solar masses that is accreting only the remnants of its original dispersed matter. If the star condenses within a dust cloud, or enters such a cloud before the consolidation of the diffuse matter is complete, the increase in mass by accretion from the cloud moves the star upward on the diagram, and the resulting path is similar to the line XZ.
It should be noted that although the evolutionary path
of the Class C stars in the CM diagram is quite different from that of
the Class A stars, and the significance of positions in the diagram, in
terms of variables other than temperature and luminosity, is also quite
different, the result of the evolutionary development is the same in both
cases. The evolution carries the stars from a cool and very diffuse condition
in region O of the diagram to a position on the main sequence that is
determined by the stellar mass. And it accomplishes the movement by means
of the same process in both cases, a process—gravitational contraction—that
is known to he operative under the existing conditions.
In sharp contrast to this straightforward gravitationally powered process, conventional astronomical theory offers a bizarre succession of twists and turns that attempt to reconcile the observational data with the upside down evolutionary sequence based on the purely hypothetical hydrogen conversion process as the source of stellar energy. As already noted, this theory requires a movement from region O. the red giant region, of the CM diagram, to the main sequence, but then finds it necessary to reverse the movement and bring the stars back to the red giant region again. The theorists have not been able to define this reverse movement without making the mass of the star an independent quantity. They have therefore abandoned any systematic connection between mass and position in the diagram, aside from that which exists along the main sequence. As Shklovsky puts it, the stars move on the diagram in a rather meandering fashion. 49
This assumption that the temperature and luminosity of a star can be totally independent of the mass is another inherently improbable hypothesis. Both of these quantities are determined by the mass along the main sequence, and the idea that the connection is completely severed under other conditions is unrealistic. Furthermore, it runs into an obvious difficulty when the hypothetical evolutionary line again intersects the main sequence on the road from red giant to white dwarf. If we examine the hypothetical evolutionary path without regard to its meanderings, what we find is a turnoff from the main sequence at a point asserted to be determined by the mass of the star, a horizontal movement to the right, and then a turn upward that continues on a diagonal line to the red giant region. From there the path extends back to the left along a rather indefinite horizonal course. A diagram that purports to demonstrate the agreement between this theoretical pattern and the observations accompanies almost all discussions of the subject in astronomical literature. This is a composite diagram, combining the CM diagrams of a number of star clusters. (See, for instance, reference 50 .)
Aside from the question as to the direction of movement, which cannot be determined from observation, the hypothetical evolutionary path agrees, in general, with the CM diagram of the globular clusters. It could hardly do otherwise, since it was deliberately designed to fit the globular cluster pattern. The agreement of the composite diagram with the hypothetical evolutionary pattern is therefore significant only to the extent that there is agreement in the case of clusters other than those of the globular cluster type. In Chapter 10 we will find that some clusters such as M 67 and NGC 188 that are classified as open clusters are actually fragments of globular clusters that have not yet lost all of their globular characteristics. To arrive at the true significance of the composite diagram we need to eliminate the clusters of this type, as well as the normal globular clusters, and examine the extent of agreement between the remaining open clusters and the theoretical pattern. When we do this we find that there is no correlation whatever. These clusters have stars along the main sequence, and in the immediate vicinity thereof, and one of them also contains some red giants. But there is no trace of the evolutionary pattern that the diagram is supposed to corroborate. The evidence that is asserted to support the contention that the stars of the open clusters evolve off the main sequence simply does not exist.
A recognition of the true evolutionary pattern, as derived from the theory of the universe of motion, makes it possible to understand the real meaning of the association of certain kinds of stars with dust clouds that has led to the belief that the stars are being formed within the clouds. Two such types of association are recognized. O associations are composed of stars of the O and B types, the largest and hottest of all stars. T associations are groups of stars of the T Tauri class, much smaller and cooler than the O and B stars. Often, but not always, the T-associations coincide with O-associations. 51 The prevailing belief that the hot massive stars are young leads to the conclusion that they were formed somewhere near their present locations. Taken together with the observed association between the O and B stars and nebulosities, this indicates that the stars of the O associations have been formed by condensation of portions of the gas and dust clouds in which they are now located. This hypothesis is currently accepted by most astronomers, but, as brought out in Chapter 1, they are unable to explain how stars can be formed from clouds of such low density. This process, says Simon Mitton, is almost a total mystery. 52
Development of the theory of the universe of motion does not provide any way whereby the dust and gas clouds of the Galaxy can condense into stars. On the contrary, it identifies still another force opposing such a condensation, the force due to the outward progression of the natural reference system, and it indicates that condensation cannot take place unless the clouds are either very much larger or very much denser than anything that exists in the Galaxy. However, it is clear from the information brought to light by this development that what is actually happening is accretion of matter from the dust and gas clouds by previously existing stars. These stars already in existence are not limited by the factor that prevents dust and gas particles from condensing into a stellar aggregate under galactic conditions; the net motion of each particle outward away from all others. All particles within the gravitational limit of an existing star have a net inward motion toward the star, and are on the way to capture. .
The clouds of dust and gas in the Galaxy are subject to forces that tend to spread them out and dissipate them. It follows that the identifiable clouds are relatively recent acquisitions by the Galaxy. As such, they are associated mainly with the relatively recent stellar acquisitions, the Class 1A stars. As we have seen, these stars are initially divided into two groups, a large group of small stars that reach gravitational equilibrium in the lower portion of the main sequence, and a smaller group of large stars that reach equilibrium well above the midpoint of that sequence. We can therefore expect the products of accretion to existing stars from the gas and dust clouds to be of two kinds, one group of hot massive stars and one group of small and relatively cool stars. These two groups required by the theory can obviously be identified with the O associations and the T associations respectively. Both groups contain some of the Class 2 stars that have been mixed with the Class 1 population since entry of the younger stars into the Galaxy.
The positions of the O and T associations in the CM diagram are entirely consistent with the accretion explanation. The upper portion of the main sequence, in which the O stars are located, cannot be reached without some accretion from the environment. The largest Class 1 stars reach the main sequence considerably below this level, and the Class 2 (and later) red giants, reconstituted from part of the matter of the O type star that exploded, are necessarily somewhat less massive than the O stars. There are no super red giants which would correspond to the evolution of an O-type star. 36 (S. J. Inglis) The stars of all classes therefore have to grow at the expense of their environment in order to reach the O status.
The T Tauri stars are found in a location generally described as above the lower portion of the main sequence. Inasmuch as this sequence runs diagonally across the diagram, it is equally correct to say that these stars are located somewhat to the right of the main sequence. As can be seen from Figure 5, this is consistent with an ongoing accretion from the surrounding cloud of dust and gas. A star that is accreting substantial quantities of such material is in essentially the same condition as one that is consolidating the final remnants of, the material dispersed by a supernova explosion. As we saw earlier, a star of this latter type (Class 2C) is moving horizontally across the CM diagram from right to left. In the latter part of this movement it occupies a position similar to that in which the T Tauri stars are found. The T Tauri position is thus in full accord with the accretion explanation. The observation that there are erratic changes in brightness 53 of these stars is also consistent with the finding that they are accreting material from the environment in substantial, and probably variable, quantities.
Let us now take a closer look at the pattern of events in the interior of an aggregate that has just become a star (of any cycle) by activating the atomic disintegration process as a source of energy. The additional energy thus released causes a rapid expansion of the star: This expansion has a cooling effect, which is most pronounced in the central regions, and as the temperature in these regions drops below the recently attained destructive limit, the energy generation process itself is shut off, accentuating the cooling effect. Eventually this cooling stops the expansion and initiates a contraction of the star, whereupon the temperature again rises, the destructive limit is once more reached, and the whole process is repeated.
A newly formed star of either Class A or Class C is therefore variable in the amount of its radiation an intrinsic. Variable as it is called to distinguish it from stars of the class whose variability is due to external causes. Almost all these stars I those below 1700 K I are, as we had expected, long period variables 54 report Neugebauer and Leighton, pioneer investigators of the infrared stars. Not all cool stars are young, but an old cool star has had time to reach gravitational equilibrium, and it is therefore small, whereas the young stars are still very diffuse—such a star has been described as nothing but a red hot vacuum—and hence they are very large. Inasmuch as they are radiating from a much larger area their total radiation is much greater than that of old stars of the same surface temperature. The bright infrared stars are thus the newly for-mea variables.
The length of the cycle, or period, of a variable star depends on the relation of the magnitude of the energy released by atomic disintegration to the total energy content of the star. When the star is very young, and its temperature is barely above the stellar minimum, the rate of energy generation is large compared to the total energy of the star, and the swings from the on to the off position of the energy production mechanism are relatively large. Such stars are therefore long-period variables. As a star grows older, its temperature and energy content increase, because the average energy production exceeds the radiation in this stage of the evolutionary cycle. The fluctuations in the rate of energy production thus represent a constantly decreasing proportion of the total energy of the star, Both the period and the magnitude of the variation (measured in terms of percent change in radiation) therefore decrease with time.
As the average temperature of the star rises, a point is eventually reached at which the temperature in the central regions during the low phase of the cycle no longer drops below the destructive limit of the heaviest element present. But this does not put an end to the variability, because by this time, or very soon thereafter, the high point of the temperature cycle reaches the destructive limit of the next lighter element, and generation of energy by destruction of this element takes place in the same kind of an on and off cycle. The fluctuations never cease entirely, but they decrease in magnitude, and are no longer evident observationally after the temperature stabilizes, or when the total energy of the star becomes so large that the effect of the variations is negligible on the scale of the observations.
One star, the sun, is so close to us that even small variations in energy production should be detectable. This subject has not yet been studied in the context of the universe of motion, but some aspects of the sun's behavior are known to be variable. The observed fluctuations in the sunspot activity are particularly noticeable. The origin of these spots is unknown, but no doubt they are initiated in some manner by the energy production process. Hence they may be giving us an indication of the variations in the output of that process that would be expected from the periodic changes. There are also some relatively long range variations, such as the decrease in energy output that caused the Little Ice Age in the seventeenth century and the increase that is producing the gradual warming in the twentieth, which may be due to variations in the nature or amount of the material accreted from the environment. In any event these are subjects that warrant some investigation. It is possible that such an investigation can be extended to more distant stars not currently classified as variables. Some observations of variations in activity similar to the sun's I l-year sunspot cycle in nearby stars have already been made.55
The theoretical explanation of the process whereby the heavier elements are built up, as set forth in Volume II, defines it as a continuous capture process that is taking place throughout the entire extent of the material sector. In the primitive aggregate of diffuse material, and in the early dust and gas clouds, the magnetic ionization level is zero, which means that there is no obstacle to the formation of any of the 117 possible elements. The time spent in this first of the evolutionary stages is so long that all of the elements are represented in the constituent dust of the clouds by the time the protostar stage is reached. Inasmuch as the build-up of the atomic structure is a step-by-step process, the initial abundance of the elements is an inverse function of the atomic mass (with some modification by other factors), but even a small amount of the very heavy elements is sufficient to initiate the atomic disintegration that provides the increment of energy which raises the dense dust cloud to stellar status.
By the time the initial supply of heavy elements is exhausted, the stellar fuel has been replenished by accretion of material from the environment, and by the continued operation of the atomic building process. All accreted matter has some heavy element content, but the addition to the fuel supply is not limited to this amount. Any matter that adds significantly to the total mass of the star serves the purpose of activating an additional source of energy. The increase in mass increases the central temperature of the star, and it thereby makes more fuel available through reaching the destructive limits of lighter elements.
Correlation of the central temperature with the mass carries with it the implication that the principal fuel supply at any given mass level is provided by a specific element. Most of the very heavy elements are present only in small concentrations, and this makes it difficult, in most instances to distinguish the points at which destruction of an additional element begins. There is, however, a relatively wide mass range, indicated by the cross-hatched area in Fig 6, in which the variability is sufficiently regular to make it evident that a single element is the principal energy source. The distinctive character of the variability in this region, which we will identify as the Cepheid zone, extends through a wide enough range of central temperatures to indicate that the energy is being derived primarily from an element that is present in the star in a higher concentration than that reached by any element of greater atomic number. The particular element that is involved cannot be positively identified without further investigation, but since lead is not only the first moderately abundant element in the descending order of atomic mass, but also the only such element in the upper portion of the atomic series, we may, at least tentatively, correlate the destructive thermal limit of this element number 82 with the central temperature corresponding to the mass range of the Cepheid zone. It should be noted in this connection that lead is the heaviest element that is stable against radioactivity in a region of unit magnetic ionization, and it therefore occupies a preferred position somewhat similar to that of iron.
The long period variables that precede the Cepheids on the evolutionary path can be correlated with the elements above lead in the atomic series. Here the quantities of energy generated as the successive destructive limits are reached are smaller, inasmuch as these elements are relatively scarce, but each increment of energy has a greater effect on the stellar equilibrium because of the smaller heat storage capacity of these low temperature stars. This accentuates the eftcct of minor variations in the incoming flow of matter from the environment, and as a result these long period variables are less regular than the Cepheids. In general, these stars are not separable into easily recognizable classes on the order of the Cepheids, but some groups of a somewhat similar nature have been identified. The RV Tauri variables. for instance, are found between the red. Mira type, long period variables and the Cepheids . 56
There are 35 elements heavier than lead in the primitive material from which the globular cluster stars were formed. The destructive limit of each of these elements establishes a central temperature for a particular group of stars in the same manner that the destructive limit of lead (presumably) establishes the central temperature, and consequently the characteristic properties, of the Cepheids. Most of the Class C stars are probably at the unit magnetic ionization level, reducing the number of stable elements above lead to ten, and the RV Tauri stars account for one of these, but trying to divide all of the variables earlier than the Cepheids into groups, and to identify the elements that constitute the principal energy source for each, is clearly impractical, as matters now stand, even if only nine more groups are involved,
The stars located in the area where the Class A evolutionary line AC crosses the Cepheid zone arc known as RR Lyrae stars. They are abundant in the globular clusters, and for this reason are also called cluster variables.
However, they are not the only Class A Cepheid stars in these clusters. One kind of a globular cluster star that we have not yet considered is a star that condenses on a large nucleus; either a pre-existing small star or an aggregate of planetary mass. When condensation of a star takes place on a nucleus of this size the line of evolutionary development is similar to that of the Class C giants, and is shifted upward on the CM diagram relative to the Class 1A path. This line enters the Cepheid zone at a location where the mass and central temperature are the same as in the region of the RR Lyrae stars, but the density and surface temperature are lower, while the luminosity is higher. The astronomers as Population know the stars of this Type II Cepheids, or W Virginis stars. In our terminology they are Class 1 Cepheids.
The changes that take place in the stars during their trip around the cycle have some effect on the position that a star of a given kind occupies within its zone of the CM diagram. One such result is the existence of a third kind of Cepheid star. A giant Class C star of the second or later cycle moves through the Cepheid zone if it has a large initial mass, or is subject to heavy accretion. As would be expected, the general characteristics of this kind of Cepheid are similar to those of the Class 1 Cepheids. Indeed, it is only relatively recently that the existence of two distinct groups of these large Cepheid type stars has been recognized. But it is now known that the Class 2C (Population 1) Cepheids are more massive, and are located higher (about 1 ~/z magnitudes) on the CM diagram than those of Class 1.57 They are also quite uniform in size and other properties. Both the large mass and the similarity in properties of these Class 2C stars are explained by our finding that they are stars reconstituted from the products of Type I supernovae, which are explosions of stars that have reached the mass limit, and are therefore both very large and very much alike. These characteristics carry over into their products.
As would also be expected, the RV Tauri variables previously mentioned are likewise separable into two distinct groups similar to the two classes of Cepheids.56
On the other side of the Cepheid zone the controlling factors are reversed. The heat storage capacity of the star is much greater, because of the higher temperatures and greater mass. Consequently, any variations, either in the rate of accretion or in the abundance of heavy elements in the accreted matter, are, to a large extent, smoothed out.
The Cepheid stars have played an important part in the advancement of astronomical knowledge because there is a specific relation between their periods and their luminosities. This is understandable as another result of the interrelation between the different properties of the stars that has been the subject of much of the discussion in this and the preceding chapter. It probably applies to most other kinds of intrinsic variables as well as to the Cepheids, but these other types of variable stars are less common, and so far, less clearly identified. It is also doubtful if any of these other classes of stars are as uniform as the Cepheids. The period-luminosity relation for the Cepheids, when properly calibrated enables the absolute magnitude of a Cepheid star to be determined from the period, an observable quantity. The relation of the absolute magnitude to the observed magnitude then indicates the distance to the star, thereby providing a means of measuring distances up to millions of light years, far beyond the limits of ordinary methods of measurement.
The explanation of the pulsations of the Cepheids and other similar types of variable stars given in this work is, of course, quite different from that found in the astronomical literature. The astronomers envision this as a mechanical vibration—just like a bell, as one textbook puts it. But the observed characteristics of the pulsation contradict this hypothesis.
A peculiar fact . . . is that the maximum brightness occurs near the time of most rapid expansion, while minimum brightness coincides with the most rapid contraction. This is contrary to any theory, which assumes a simple pulsation of the entire stellar body. It might indeed seem that the star should be brightest and hottest shortly after the contraction has brought it to a state of highest density and pressured 58 (R. Burnham)
Like so many of the other peculiar facts that are noted, but disregarded, in current practice, this one is giving us a message. It is telling us that the prevailing theory of the pulsation is wrong. The theory of the universe of motion now reveals just what it is that is wrong. The pulsation is not a mechanical vibration; it is thermally powered. The interplay between two processes expansion and energy generation—is the cause of the periodicity. The maximum brightness occurs near the time of maximum expansion because this is the point at which the generation of energy at the maximum rate has persisted for the longest time.
Except for some portions of the stellar content of nickel and other elements close to iron that escape because of local variations in the conditions in the central regions of a star, the elements heavier than iron are destroyed in the production of energy during the life of the star, and in the Type I supernova explosion which terminates that life if the star arrives at the temperature limit of iron. The building up of these elements has to start approximately from scratch again, but the period of expansion and re-aggregation of the explosion products is long enough to bring the heavy element concentration in the second-generation protostars back somewhere near that in the protostars of the first cycle. Meanwhile the concentration of iron and the elements of lower atomic mass has been increasing without interruption, and the total heavy element content of the class 2C stars (usually expressed as the percentage of elements above hydrogen or above helium, or as the ratio of the heavier elements to hydrogen) is substantially greater than that of the Class 1A stars.
The same atom building processes are effective in the environment of the stars the interstellar space. The heavy element content is determined by the age of the mutter, irrespective of whether that matter is in the form of dust and gas or is incorporated into stars. As noted in Chapter 3, the current view of the astronomers is that the heavy elements are formed in the interiors of the stars and are scattered into the environment by supernova explosions. On this basis, the heavy element content of young stars is greater than that of old stars because the proportion of heavy elements in the raw material available for star building increases as the galaxy ages.
Although this view currently enjoys quite general acceptance, more and more anomalies are appearing as evidence from observation continues to accumulate. In addition to the many items of evidence contradicting this hypothesis that have been discussed in the previous pages of this volume, we may now note that there is evidence indicating that the heavy element content in the interstellar matter of the local environment is not increasing. Martin Harwit has considered this situation at some length. He observes that the similarity in abundances (that is, in chemical composition, as indicated by the spectra) of different classes of stars in the Galaxy—B stars, red giants, planetary nebulae, etc.—is somewhat puzzling. 59 These similarities lead him to this conclusion: These analyses show that throughout the lifetime of the Galaxy the interstellar matter has had an almost unchanged composition. This is definitely in conflict with the basic premise underlying the currently accepted explanation of the difference in composition between the old and young, stars: the assumption that the interstellar medium is continually enriched with heavy elements cooked in the stars and scattered into the environrllent.
Of course, our findings also require the heavy element content of any given quantity of matter to increase with age, but the existing interstellar matter is not the same matter that occupied this region of space in earlier times. All galaxies are pulling in diffuse material from their surroundings, material, which, according to our findings, is relatively young. For example, Harwit refers to a recently discovered, apparently continuous, infall of gas from outside the Galaxy. As noted in Chapter 2, the larger galaxies are also capturing some immature globular clusters in which the constituent dust clouds have not yet consolidated into stars. Meanwhile, the stars are accreting the older interstellar matter. It is quite likely that these two processes come near enough offsetting each other to leave the average composition of the interstellar material in the local environment nearly constant. Harwit's conclusion as to the constancy of composition is therefore consistent with the theory of the universe of motion insofar as it applies to the situation in the outer regions of spiral galaxies. The proportion of heavy elements should theoretically be greater in the older regions of the galaxies, but these are not accessible to detailed observation, as matters now stand.