CHAPTER 10
Evolution - Galactic Stars
When a globular cluster finally falls into the Galaxy and becomes subject to the forces of the galactic rotation, some rather drastic changes take place, and the CM diagram of the cluster is modified to the point where it is no longer recognizable without some understanding of the effects that are produced by the galactic forces. These effects are illustrated in Figure 12, which is the CM
diagram of the cluster M 71. In this, and the other CM diagrams that will follow, any areas in which the star concentration is sufficiently above average to warrant special consideration are cross-hatched, while sparsely populated areas that may or may not belong in the diagram are outlined by dashed lines. M 71 is on the borderline, and has been classified as an open cluster by some observers, although it is now more commonly regarded as a globular.120 From this uncertainty as to its true status we can deduce that it is a globular cluster that has reached the edge of the galactic disk and is on the way to becoming an open cluster, or more likely, will break up into a number of open clusters. The CM diagram of this cluster is described by Burnham as having a “red giant sequence resembling that of a globular” , with “an unusually large scatter and a steeper slope than normal” , but lacking the usual horizontal branch and extension to the main sequence. Thus, even for the astronomers, this diagram leaves a great deal to be explained. In the context of the new information developed in this volume, this diagram has even less resemblance to that of a normal globular cluster, as a “steep slope” of any of the lines in the diagram is inadmissible. The theoretical positions of all three of the evolutionary lines are fixed. The portion of the diagram in the upper right that is being identified as a wide giant branch is too steep to be the red giant line OA, and the slope of the cross-hatched section at the lower end of the diagram is not steep enough to be the evolutionary line AB. The diagram looks like a misfit.
So let us examine the situation from a theoretical standpoint. When the cluster enters the rotating stream, the immediate effect is that the loosely attached matter is stripped away, both stars from the cluster as a whole, and particles from the individual stars. As noted earlier, the differential gravitational forces are already reducing the sizes of the clusters very significantly as they approach the Galaxy, and this loss of stars is accelerated when the rotational forces are added to the radial gravitational effect. Reduction in size has the collateral result of reducing the central condensation.
The globular clusters do not move freely through the field of stars in the manner described by Hoyle in the statement quoted in Chapter 2; they have to push the stars aside in order to clear their paths. But the individual stars do move through the interstellar medium. In so doing they lose the unconsolidated material by which they were surrounded, and from which they were drawing the additional mass that enabled them to follow the normal evolutionary paths. The loss of this material stops the growth of the star, and prevents it from reaching the critical density by the accretion route. However, the star is still subject to the compressive forces due to the gravitational effect of the cluster as a whole, and these forces, together with the self-gravitation of the star, compress the existing gaseous aggregate, and move it downward on the CM diagram along a line of constant mass.
The theoretical results of the stripping action on the locations of the stars in the CM diagram are illustrated in Figure 13. Diagram (a) is the regular cluster diagram for a cluster in which the most advanced stars have just recently reached the main sequence. Diagram (b) shows where these stars would be if
the cluster remained isolated long enough to permit the evolutionary development to bring most of the stars down to the main sequence, with only the least advanced stars still on the path AB. If the cluster falls into the galaxy while it is in the condition shown in (a), the atmospheres of dust and gas from which the stars along the path OA are growing are swept away. These stars are then unable to move forward along this line. Instead of continuing on to the vicinity of point A before the supply of material for accretion is exhausted, they are deprived of this material almost immediately on entering the rotating stream. As a result, each star along the line OA leaves that line from whatever location it may happen to occupy at the time of entry, and moves downward on the diagram along a path parallel to AB, a line of constant mass.
Thus the effect of the interaction with the interstellar medium is to replace the relatively narrow path AB with a path that has the same slope and length, but has a width equal to OA. This path has a lower limit XX’ parallel to OA that represents the extent to which evolutionary progress has taken place since the beginning of the capture process. As the evolution continues, the line XX’ moves downward on the diagram. The theoretical CM diagram for a captured cluster in a relatively early stage is then similar to (c).
When the last stars have left OA on the downward path, their positions lie along a line YY’ parallel to OA, constituting an upper limit to the stellar positions on the diagram. Summarizing this process, in the first interval after the entry of the cluster into the rotational stream the stars are located in the area between OA and the limit XX’. As the downward movement continues, the last stars leave OA, and in the next stage the star locations are between XX’ and YY’. Finally XX’ is cut off by the main sequence, and in this last portion of the downward movement, the stars are located between YY’ and the main sequence, as indicated in diagram (d). After the first stars reach the condition of gravitational equilibrium, the main sequence population continues to increase throughout the remainder of the evolutionary development.
If we apply diagram (c), which shows the theoretical positions of the stars of a newly captured cluster, to the M 71 situation, everything falls into line, M 71 shows both of the characteristics previously mentioned as those of a greatly reduced globular cluster that is entering the fringes of the rotating galactic disk: a relatively low central condensation and a relatively small size. Its diameter is said to be about 30 light years. Double this value would still be below average. The giants exceed 200 light years. The relation of the observed locations of the stars of this cluster to the theoretical diagram is shown in Figure 14. Here we see that the observations fit neatly within the theoretical parallelogram. The absence of identifiable stars on the line AC, the horizontal branch, is explained by two results of the stripping process: (1) no new stars are moving into the AC region, and (2) the relatively small number of stars that were located on this line prior to the start of the capture process were scattered over the triangular area ABC by the same kind of a downward
movement that occurs in the more heavily populated region on the other side of the path AB.
The M 71 pattern is not uncommon. Five other clusters out of those examined in this investigation also show the same kind of evidence that they are just entering the rotational stream only one is in the intermediate range where both the upper (YY’) and lower (XX’) limits are observable. The more advanced clusters that are limited to the lower section of the diagram between YY’ and the main sequence are again fairly numerous. But here we find that a new factor has entered into the determination of position on the CM diagram. The main sequence sections of some of these more advanced clusters are well defined, and they show that the clusters in this stage of evolution are subject to an upward displacement of the main sequence.
In the cluster M 67, which is regarded as the prototype of this class of cluster, the shift is about 2.6 magnitudes. Figure 15 is the CM diagram of M 67. As can be seen, this diagram is similar to those of M 71 and other newly captured clusters, but a considerable number of the stars of the cluster have reached the main sequence, and they do not lie on the line BC, the lower line in Figure 15. Instead, they follow a line parallel to BC, but above it by the amount of
the displacement. Otherwise, the stellar positions are entirely Norma It is particularly significant that the upper limit of the populated area, the line designated as YY’ is sharp and distinct, because this line has a definite theoretical relation to the evolutionary pattern. It has to be parallel to the theoretical line OA, which is specifically defined mathematically, even though M 67 actually has no stars in the upper areas of the complete globular cluster diagram.
In order to understand the origin of the displacement of the main sequence, the gravitational shift, as we will call it; the nature of the equilibrium on the main sequence needs to be recognized. Basically, this is an equilibrium between the gravitational force (or motion) and the force (or motion) of the progression of the natural reference system. In the dust cloud state in which the giant stars originate there are two gravitational components, the self gravitation of the star and the gravitational effect of the cluster in which the star is located. The net resultant of all forces is inward, and the star therefore contracts. As the contraction proceeds, the net inward force weakens, and ultimately the point is reached where the inward and outward forces are equal. This is the main sequence of the cluster.
Two of the three force components, the progression of the natural reference system and the self-gravitation of the star, are constant for a star of a given mass and volume but the third component is variable and it determines the location of the main sequence equilibrium The stars in a globular cluster occupy equilibrium positions where there is no net force in either direction. In this case, therefore, the variables force component is zero in the equilibrium condition, if the contraction is competed within the cluster. Here the stellar equilibrium within the cluster is identical with that of an isolated star in space.
The stars of the Galaxy also occupy equilibrium positions, but the galactic situation is not a full three-dimensional equilibrium. It has been attained in part by balancing a portion of the inward gravitational effect of the galaxy as a whole against the outward component of the rotational motion. This is a one-dimensional vectorial motion, and while it counterbalances the gravitational motion so far as the representation in the conventional spatial reference system is concerned, it does not offset the full effect of a motion such as gravitation that is effective in all three scalar dimensions. Thus there is a second gravitational component in the main sequence force equilibrium of the galactic stars. The component due to self-gravitation at equilibrium is reduced accordingly; that is, the contraction of the star stops at a lower density (or expands back to that density). This puts the main sequence of the galactic stars somewhat higher on the CM diagram than the main sequence of the globular cluster stars. As indicated earlier, the difference is about 0.8 magnitudes.
This is a theoretical conclusion that takes us into a hitherto unexplored area of astronomy, but it is not without observational support. We note, for instance, that when the main sequence of the clusters is lowered to the 4.6 level, the area of the diagram included between this and the galactic main sequence at 3.8 magnitude includes the positions of a group of stars known as sub-dwarfs. “The location of metal-poor subdwarfs is puzzling” , say M. and G. Burbidge, “because they seem less bright than [galactic] main sequence stars of comparable surface temperature and hence lie below the main sequence.” But then these authors go on to give us the information about the subdwarf stars, which, in the light of the theoretical conclusions that we have just reached, provides the explanation.
These subdwarfs… are not traveling with the sun in its giant orbit around the hub of our galaxy, and consequently they are moving with high speeds relative to the sun and in one general direction—that opposite to the direction in which the galactic rotation is carrying the sun.102
According to our findings, these are stars that have escaped from globular clusters, and have entered the Galaxy from outer space. The fact that they are relatively metal-poor supports this conclusion. But in any event, whatever their origin may have been, the significant point is that they are not “traveling with the sun”; that is, they are not participating (or not participating fully) in the rotation that we find to be the cause of the 0.8 magnitude gravitational shift of the galactic field stars. Actually, they can hardly avoid being affected to some extent by the rotational forces. It follows that they should theoretically be distributed throughout the region between the two main sequence locations. This is just where they are found.
Another item of evidence supporting the theoretical identification of the 0.8 magnitude difference as a gravitational shift will be forthcoming in Chapters 11 and 12, where it will be shown that the gravitational equilibrium applicable to objects moving in time is related to the 4.6 magnitude level, rather than to that of the galactic main sequence.
With the benefit of the foregoing information we are now in a position to explain the gravitational shifts of M 67 and other open, or galactic clusters. M 67 is a remnant, or fragment, of a globular cluster that has quite recently fallen into the galaxy. It has reached the point where it has begun building up a main sequence population, although its slower stars are still in the process of completing their evolution along the globular cluster path AB and its rightward extension. It is one of the earliest of the objects classified as open clusters, and has the principal characteristics of a recent arrival: a star population that is large for an open cluster, a relatively compact structure, and a position high above the galactic plane. The big decrease from the globular cluster size and the entry into the galactic disk have destroyed the structural stability that existed in the parent globular cluster, and M 67 has begun the expansion that will ultimately terminate its existence as a separate entity.
Now that they are within the Galaxy, the M 67 stars are subject to the same forces as the galactic field stars, and in addition are subject to the residual cohesive force of the cluster. Expressing this in another way, we can say that the stars of the main sequence of the open cluster have not yet completed their transition to gravitational equilibrium. The temporary equilibrium represented by their main sequence positions includes a diminishing component from the gravitational force of the cluster as a whole. The cluster stars will not reach main sequence positions comparable to those of the field stars of the Galaxy until the cluster expansion is complete, and this extra force component is eliminated. In the meantime, the main sequence of each cluster will be above that of the field stars by an amount depending on the remaining cohesive force of the cluster. This gravitational shift is greatest where the clusters are young, large, and compact, like M 67, and decreases as the cluster becomes older, smaller, and looser.
As we saw earlier, when galaxies reach the size at which they capture substantial numbers of globular clusters they also begin to pull in some unconsolidated clusters, aggregates that are still merely clouds of dust and gas. These clouds arrive too late in the elliptical stage of galactic evolution to have much effect on the properties of the observed elliptical galaxies, although they may be responsible for the occurrence of concentrations of blue stars in some of these galaxies. But when the elliptical structure spreads out to form the spiral, the stars of the galaxy are mixed with the recent acquisitions of dust and gas. The stage is then set for a period of rapid advance along the path of stellar evolution, as the availability of this kind of a supply of material accelerates the evolutionary process.
During the time that the mixing is taking place the dust and gas exist in widely different concentrations in different parts of the galactic structure. The average concentration in the outlying regions that it reaches first is sufficient to support an accretion rate that results in a continuing increase in the mass of the average star. After arrival at the main sequence, the very small stars, those whose growth was cut off prematurely by the entry of the cluster into the Galaxy, take up relatively permanent positions in the lower sections of this sequence, while the larger stars accrete matter and move upward along this path. Since the stars of a cluster, aside from the few captured strays, were all formed in the same event, and are of approximately the same age, most clusters occupy only a limited sector of the evolutionary cycle. The active sector does not expand appreciably, but merely moves forward as the cluster ages and passes through the various evolutionary stages.
In the Hyades, Figure 16(a), a cluster somewhat older than M 67, a few stars still remain on the contraction path AB, but the majority have reached the main sequence. Figure 16(b) represents a still more advanced cluster, the Pleiades, in which the last stragglers have attained gravitational equilibrium, and the main body of the active stars has moved up along the main sequence. Whether or not the Pleiades cluster is actually older than the Hyades is uncertain, as the evolutionary age is not necessarily coincident with the chronological age. The Pleiades are located in an observable nebulosity, and the accelerated accretion from this source may account for the more advanced evolutionary stage.
The possible variations in the rate of development of these nearby clusters are of particular interest in connection with the possibility that many of the open clusters in the local region of the Galaxy may be fragments of the same disintegrated globular cluster. It has already been recognized that some of these clusters are similar enough to imply a common origin. This has been suggested, for example, in the case of Praesepe and the Hyades.121 The principal objection that has been raised to this hypothesis is that the clusters arc too tar apart (the distance between these two is over 450 light-years) to have originated in the same event. This conclusion is, of course, based on conventional astronomical theory. When it is realized that the open clusters are fragments of globular clusters this objection is eliminated, as it is evident
that fragments of a disintegrated cluster could be distributed over much greater distances than those that are observed.
In any event, the greater density of the M 67 class of clusters and their higher galactic latitude, taken together with the observed expansion of all open clusters, definitely establish the M 67 class as younger than the main sequence clusters such as the Pleiades and the Hyades. This conclusion, previously reached, is now corroborated by the relative magnitudes of the gravitational shifts. Those of the M 67 class average about 2.5 magnitudes, while those of the main sequence clusters are not much above the 0.8 level of the field stars.
Extension of the findings with respect to accretion by the main sequence stars indicates that continued development of the Pleiades cluster will eventually bring the hottest stars in this group to the destructive limit at the top of the main sequence, and will cause these stars to revert back to the red giant status via the explosion route. In the Perseus double cluster, Figure 17, such a process has already begun. Here the main body of stars is in the region just below the upper limit of the main sequence, but a number of red giants are also present. We can identify these giants as explosion products, stars of Class 2C, rather than new stars, Class 1A, as this identification keeps all of the stars in the cluster in an unbroken sequence along the evolutionary path, whereas if these were young stars of the first generation they would be unrelated to the remainder of the cluster. The presence of 2C giants implies that there are also young white dwarfs in this cluster, but they may be still in the invisible stage.
Some binary stars are also reported to be present in clusters such as the Hyades and the Pleiades. In these clusters, however, the A components of the binaries are on the main sequence, and there is a wide evolutionary gap between them and the Class 1 main sequence stars of the clusters. There are several possible explanations of their presence; ( I ) they are not actually members of the clusters, (2) they arc strays, older stars that were picked up during the condensation of the globular clusters, or during their subsequent travels, or (3) they were stars from the horizontal branch of the same globular cluster whose vertical branch produced the Class 1 stars of the open cluster. The cluster diagrams indicate that the stars of the two branches reach the main sequence at about the same time. Consequently there is an evolutionary gap between them that is just about right to account for the presence of some Class 2 (binary) stars in the Class 1 main sequence clusters. It seems probable that alternative (3) is the source, or at least the principal source, of these binary stars.
It is important to note at this point that in the context of the theory of the universe of motion, the presence of observable nebulosity is not necessary to account for the position of the hotter stars of the cluster at the top of the main sequence. As explained earlier, the theory definitely requires continued stellar growth even under conditions where the density of the stellar medium is no greater than average. This is something that cannot be confirmed
observationally with currently available instruments and techniques, but neither can it be disproved. Thus, this aspect of the theory is not inconsistent with anything that is actually known, which is all that is required in the case of an integrated general theory that is fully verified in other areas.
It is significant, in this connection, that current astronomical theory is inconsistent with the observations. This theory places the star formation in dense galactic nebulae. The location most commonly cited as a stellar birthplace is the Great Nebula in Orion, and the association between this nebula and a large group of hot O and B type stars is offered as evidence of recent formation from the existing dust-and gas cloud. But no nebulosity can be detected in the Perseus cluster, or in NGC 2362, another similar cluster that has been extensively studied, or in a number of other clusters in which O and B stars are prominent, while most of the main sequence clusters, such as the Pleiades, that do have associated nebulosity have no O type stars. It is commonly recognized that there is a contradiction here that calls for an explanation, but since such contradictions abound in astronomy, it is not taken as seriously as the situation actually warrants.
Some of the open clusters evidently carry over into Class 2B, as there are a large number of loose, somewhat irregular, clusters that have second generation characteristics. Here we find a substantial proportion of giant and subgiant stars, indicating that the clusters are either considerably older or considerably younger than a main sequence cluster such as the Pleiades. These clusters do not have the characteristics of the M 67 class, the predecessors of the Pleiades type of cluster, and their structure (or lack of structure) indicates that they have undergone considerable modification. We can therefore conclude that they are older, and that their giant stars belong to Class 2C. This conclusion is supported by evidence indicating that large proportions of the stars of these clusters are binaries.
Up to this point no more than casual consideration has been given to the rotation of the various astronomical objects that have been discussed, because the significance of the information available on this subject is not clearly indicated as long as each individual situation is considered in isolation. We have now reached the point, however, where we can put together enough information from different sources to show that there is a general correlation between rotation and age throughout the astronomical universe.
The earliest structures, both the globular clusters and the stars of which they are composed, have little or no rotation. As explained earlier, this is easily understood as a consequence of star and cluster formation under conditions in which only radial forces are operative to any significant degree. But it confronts conventional astronomical theory with difficult problems. The desperate attempts of the theorists to read some signs of rotation into the observations of the globular clusters as a means of accounting for the stability of these structures have already been discussed. In application to the stars, this problem is somewhat less acute, as the stars actually do rotate, and the issue here is a matter of origin and magnitude.
According to J. L. Greenstein, the average rotational speeds of stars of spectral class G and fainter are less than 25 km/sec. His estimates of the giant stars show an increasing trend up to about 200 km/see for spectral classes A3 to A7, with a decrease thereafter. The peak for the “dwarf” class (that is, the main sequence stars) is placed at a somewhat higher luminosity, in classes B5 to B7, and is estimated at 250 km/sec.29 The existence of these peaks does not mean that the rotation actually decreases in the largest stars. These are surface velocities, and the decrease is merely a reflection of the slowing of the speed of the outer layers of these stars, a differential effect that is evident even in stars as small as the sun. Current theory offers no explanation as to why speeds of these particular magnitudes should exist. Indeed, Verschuur points out that, on the basis of the prevailing theories, they should be much greater.
The simplest calculations for star formation suggest that all stars should be spinning very, very fast as a result of their enormous contraction from cloud to star, but they do not do so. Why not? The answer is far from known at present.114
Furthermore, there is direct evidence that the rotational speed is a function of age. For example, A. G. Davis Philip reports that the rotational velocities of Ap and Am stars decrease with increasing cluster age (which is decreasing age, according to our findings).122 We might also note that the question as to what happens to the rotational speed as stars go through the contortions that are required by present-day evolutionary theory receives practically no attention.
Against this background, the simple, observationally confirmed, picture of the rotational situation derived from the theory of the universe of motion provides a striking contrast. On the basis of this theory, all of the primary astronomical objects—stars, star clusters, and galaxies—originate with little or no rotation, and acquire rotational velocities as a consequence of the evolutionary processes. This increase in velocity is primarily due to angular momentum imparted to these objects during the accretion of matter. Globular clusters, which have little opportunity for accretion, acquire little or no rotation. The larger galaxies and the stars of the upper main sequence, which grow rapidly, on the astronomical time scale, increase their rotational velocities accordingly.
From the nature of the evolutionary processes, as they have been described in the preceding pages, it is apparent that no aggregate consists entirely of a single stellar class. However, the very young aggregates approach this condition quite closely, inasmuch as they are composed of young stars, and the only dilution by older material results from picking up an occasional stray that has been ejected from an older aggregate. Aside from these interlopers, the earlier globular clusters are pure Class 1A, and their CM diagrams are somewhere between a concentration at the initial point of the diagram at the extreme end of the red giant region and a distribution similar to that of M 3, Figure 3.
As brought out in the preceding pages, the evolutionary ages of the observable globular clusters are correlated with their distances from the Galaxy. On first consideration, the existence of such a relation may seem rather surprising, but it is an inevitable result of the kind of a cluster formation process that was described in Chapters 1 and 2. In the equilibrium condition from which the contraction of the group of proto-clusters begins, the proto-clusters in the outer regions of the group are moving inward, exerting a compressive force on those closer to the center of the group. Thus there is a density gradient from the periphery of the group to one or more central locations, just as there is a similar gradient from the outer regions of the clusters to their centers after they begin contracting individually. These density centers are the locations in which the condensation into stars first takes place, and the combination of the clusters into galaxies begins. Ultimately they become the locations of the major galaxies of each group. The density gradient from the periphery of the proto-group to the condensation centers then takes the form of a gradient from the gravitational limits of the major galaxies to the locations of those galaxies.
The basic physical process in the material sector of the universe is aggregation in space. Growth of the aggregates proceeds by a mechanism called capture, if it occurs on an individual basis, or condensation, if it takes place on a collective basis. The rate of growth is primarily a matter of the density of the medium from which the material is being drawn. Condensation does not occur at all unless the density exceeds a certain critical value. Capture is not so limited, but the rate at which it occurs depends on the probability of making contact, and that probability is a function of the spatial density of the entities subject to capture. All of the aggregation processes therefore speed up as the clusters move toward the Galaxy and into a denser environment. This accounts for the evolutionary changes, already noted, that take place during the travel of the globular clusters from the distant regions of intergalactic space to the point at which they end their existence as separate entities by falling into the Galaxy.
The aggregation of matter on the atomic scale that produces successively heavier elements follows the same general course as the aggregation of the dust and gas particles into stars. The atom-building process, as described in the previous volumes of this series, is also a capture process, and it, too, proceeds at a rate that depends on the density of matter in the environment.
Current estimates of the densities in the different regions through which the clusters pass give a general indication of the magnitudes that are involved. The following are some recent figures:123
| Density (g/cm3) | ||
|---|---|---|
| Intergalactic space | 10-31 | |
| Space near edge of galaxy | 10-28 | |
| Interstellar space | 10-24 | |
On this basis, the density increases by a factor of 1000 during the travel of the cluster from a distant point of origin to the edge of the Galaxy. Here, then, is the explanation for the differences in composition between the distant clusters and those near the Galaxy that were described earlier. After entry into the galactic environment the increase in density and the corresponding evolutionary changes are still more rapid.
It is not possible to follow the evolutionary cycle of the stars in the distant galaxies in the same detail as in our own galaxy, but we can apply our findings from the study of evolution in the Galaxy to an explanation of some of the changes in the observable features of these other galaxies. We can deduce that the small elliptical galaxies, including the distorted members of this class currently classified as irregular, are more advanced than the average distant globular cluster, and are in an evolutionary stage comparable to that of the most mature of those clusters. On the basis of the classification that we have set up, this means that they are composed of a mixture of the IA and 1B classes of stars.
The older and larger elliptical galaxies (not including the giant spheroidals, which are not classified as elliptical in this work) are in the same evolutionary stage as the earliest open clusters, and the CM diagrams of M 67 and the Hyades are representative of the phases through which these elliptical galaxies pass. It should be noted, however, that because of the continuing capture of younger aggregates, the early end of the age distribution is not cut off in the galaxies as it is in the clusters. The CM diagram for an elliptical galaxy in the same evolutionary stage as the Hyades would extend the sector occupied by the Hyades stars all the way back through the globular cluster sector to the original zone of star formation.
The rapid evolution in the early spiral stage eliminates most of the 1A stars, except those in the incoming stream of captured material. Aging of these spirals then results in the production of second generation stars, beginning with Classes 2C and 2D. All of these stars, both the giants (2C) and the white dwarfs (2D), are moving toward the main sequence, on reaching which they enter class 2B, the class to which the sun and its immediate neighbors belong. There are no giants among these local stars, but the presence of white dwarfs in such systems as Sirius and Procyon, and the existence of planets, shows that the local stars passed through the explosion phase fairly recently. We may interpret the lack of giants as indicating that the former giants, such as Sirius, have had time to get back to the main sequence, while their slower white dwarf companions are still on the way. It is not certain that all of the nearby stars actually belong in this same evolutionary group, as some younger or older stars may also be present as a result of the mixing due to the rotation of the galaxy and the gravitational differentials, but there are no obvious incongruities.
The 2B stars in the regions of average accretion or above move upward along the main sequence in the same manner as they did when they were 1B stars of the first cycle, and again undergo the Type I supernova explosions. Eventually they recondense into stars of the third cycle, Classes 3C and 3D. These are three-member systems, if only one of the stars of the Class 2 binary system has exploded, or four-member systems if both have gone through the explosion phase. As indicated earlier, a considerable number of such multiple systems are known.
Theoretically, this movement around the cycle will continue until the matter of which the star is composed reaches its age limit, providing that the environment is favorable for growth, but as mentioned in the discussion of the spiral structure, the contents of the galaxies are in a physical condition that has the general characteristics of a viscous liquid. In such an aggregate the heavier material moves toward the center of gravity, displacing the lighter units, which are concentrated preferentially in the outer regions. This process is slow and irregular because of the viscosity and the effects of the galactic rotation, but there is a general tendency for the older and heavier systems to sink toward the galactic center, into regions where the supply of material for accretion is limited. One six-member system, Castor, is frequently mentioned in the astronomical literature, but apparently systems of this size, systems of the fourth cycle, are scarce in the readily observable regions of the Galaxy. In view of the smaller amount of material available to the stars in the unobservable regions closer to the galactic center, and the increased competition for the material that is available, because of the higher concentration of stars, it is quite possible that the movement around the evolutionary path is limited to four or five cycles.
Some evidence suggesting continuation to additional cycles is available from the cosmic rays. As explained in Volume 1, the nature of the process whereby matter is transferred from the material sector to the cosmic sector, and vice versa, is such that this matter is near its age limit before being ejected from the sector of origin. The cosmic iron content of the cosmic rays (the incoming matter from the cosmic sector) is something on the order of 50 times that of the estimated iron content of the local main sequence (Class 2B) stars. If taken at its face value, this indicates that the evolutionary development, which causes the increase in the iron content, must extend into more than two or three additional cycles beyond the 2B stage. However, as noted earlier, the spectra of the stars tell us only what is present in the outer regions, and there is reason to believe that the iron content of the older stars in the local environment is substantially greater than indicated by the spectroscopic data. For the present it seems appropriate to interpret the cosmic ray composition as evidence favoring the higher iron content of the Class 2B stars rather than as indicating evolution beyond four or five cycles.
In either case, however, the continuation of the accretion process into a number of cycles means that the proportion of large stars (products of the explosion of stars of maximum size) in the galactic population increases as time goes on. Inasmuch as the oldest stars are concentrated toward the galactic center, it follows that the number of large stars in the central regions of the Galaxy is considerably greater than would be expected from the proportions in which they are observed in the local environment. As we will see later, the presence of this large population of big stars in the central regions of the major galaxies has some important consequences.
The fact that the development of the spiral structure antedates the appearance of the second-generation stars enables defining the general distribution of the stellar classes of the Milky Way galaxy and similar spirals. With the qualification “except for strays from older systems,” which has to be understood as attached to all statements in the discussion of stellar populations, we may say that the stars of the second and later generations, Class 2C and later, are confined to the galactic disk (including the arms) and the nucleus. The early first generation stars, Class 1A, are distributed throughout the outer structure. They constitute practically the entire halo population. The main sequence stars of the first generation. Class 1B. occupy an intermediate position, most prominently in the spiral arms.
The identification of the conspicuous hot and luminous stars of the upper main sequence with the spiral arms was the step that led to the original concept of two distinct stellar populations. However, the information that has been developed herein shows that the galactic arms actually contain a very heterogeneous population, including not only stars from the entire first evolutionary cycle, but also stars from several, perhaps nearly all, of the later cycles.
Observational difficulties limit our ability to follow the evolution of the galaxies beyond the stage of the spiral arms by studying the individual stars, but we can derive some further information from the character of the light that is being received from the inner regions. Since the stars in the galactic nucleus are older than those in the disk, they should be more advanced from an evolutionary standpoint, on the average. This difference in age is reflected in a difference in color. However, the correlation is not directly between color and age, but between color and the positions of the stars in the evolutionary cycle.
It should be realized that the great majority of all stars are red. Consequently, we can expect red light under all conditions except where the stellar population includes an appreciable number of the relatively rare blue and white stars of the upper end of the main sequence, and then only because the emission from these hot stars is so much greater than that from the red stars that even a small proportion of them has a major effect on the color of the aggregate as a whole. The hottest stars may be thousands of times as luminous as the average Class 1 star. Thus the color of a galaxy, or a portion thereof, does not identify the stage of evolution of the constituent stars. It merely tells us that the aggregate does, or does not, contain a significant number of stars in that part of an evolutionary cycle which extends into the upper end of the main sequence. The particular cycle to which these stars belong cannot be determined from this information, but since the color changes in galaxies take place gradually, the characteristics of the light emitted by a galaxy, or one of its constituent parts, supplement the evolutionary criteria previously identified.
The integrated light from the larger elliptical galaxies belongs to the spectral type G (yellow). In the early spirals the emission rises to type F (yellow white), or even type A (white) in some cases, because of the large number of Class 1B stars that move up to the higher levels of the main sequence. As these stars pass through the explosion stage and revert to the 2C and lower 2B status, accumulating to a large extent in the galactic nucleus, the light gradually shifts back toward the red, and in the oldest spirals the color is much like that of the ellipticals. Summarizing the color cycle, we may say that the early structures are red, because they are relatively cool, there is only a small change in the character of the light during the development of the elliptical galaxy, then a rapid shift toward the blue as the transition from elliptical to spiral takes place, and finally a slow return toward the red as the spiral ages.
Current astronomical theory correctly identifies the stars of the nuclear regions of the galaxies as older than those in the spiral arms, but reaches this conclusion by offsetting one error with another. This theory identifies the globular cluster stars as older than the main sequence stars of the galactic arms. This is incorrect. But then the theory equates the stars of the nucleus with those of the globular clusters. This, too, is an error, but it reverses the first error and puts the stars of the nucleus in the correct age sequence relative to those of the galactic arms. However, this superposition of errors leaves the astronomers with an open contradiction of their basic assumption as to the relation between the age of a star and its content of heavy elements. This embarrassing conflict between current theory and the observations is beginning to be a subject of comment in the astronomical literature. For example a 1975 review article reports measurements indicating that the “dominant stellar population in the nuclear bulges of the Galaxy and M 31 consists of old metal-rich stars.”124 As the authors point out, this reverses the previous ideas, the ideas that are set forth in the astronomy textbooks. The expression “old metal-rich stars” is, in itself, a direct contradiction of present-day theory. The whole fabric of the accepted evolutionary theory rests on the hypothesis that old stars are metal-poor. The existence of a greater metal content in the central regions of the galaxies is apparently not contested. Harwit makes this comment:
There also seems to exist abundant evidence that the stars, at least in our Galaxy and in M 31, have an increasingly great metal abundance as the center of the galaxy is approached. The nuclear region appears to be particularly metal rich, and this seems to indicate that the evolution of chemical elements is somehow speeded up in these regions8
In the light of our findings it is, of course, unnecessary to assume any speeding up of stellar evolution in the central regions of the Galaxy. All that is needed is to recognize that the stars in these regions are the oldest in the galaxy, and their evolution has continued for a long period of time.
This chapter completes our discussion of the more familiar areas of the astronomical universe. In the remainder of this volume we will be exploring hitherto uncharted regions, aspects of astronomy where the currently accepted ideas are almost completely wrong, because of the strangely unquestioning acquiescence in Einstein’s assumption that the experimentally observed decrease in acceleration at high speeds is due to an increase in mass, and that speeds in excess of that of light are therefore impossible. As has been demonstrated in the course of the development of the theory of the universe of motion, the speed of light is a limit applying only to one-dimensional motion in space, and there are vast regions of the universe in which motion takes place in time, or in multi-dimensional space. Most of these are inaccessible to observation from our position in the universe, but some of the entities and phenomena of these regions do have observable effects on the material sector, the sector in which we make our observations. These effects will constitute the subject matter of the remaining chapters.
Since these subjects will be approached from a totally different direction, the conclusions that will be reached will differ radically, in many cases, from those currently accepted by the astronomical community. As we begin our consideration of these new, unfamiliar, and perhaps disturbing, findings in the admittedly poorly understood areas of astronomy, it will therefore be well to bear in mind what the theory of the universe of motion has been able to do in the presumably quite well understood astronomical areas. It has produced an evolutionary theory that turns the conventional astronomical theories upside down, and it has identified a variety of observational data that confirm the validity of the revised evolutionary sequence, including two sets of observations, the densities of the different classes of open clusters, and the metal content of the stars in the central regions of the galaxies, that provide definite proof that evolution takes place in the reverse direction. This ability of the new theory to correct a major error in current thought with respect to the phenomena of the better known regions should inspire some confidence in the validity of the conclusions that are derived from that theory in the relatively unknown astronomical areas, particularly when it is remembered that scarcity of observational information is not a major handicap to a purely theoretical structure of thought, whereas it is usually fatal to theories, like most of those in astronomy, that rest entirely on observational.