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O.N. Karavashkina and S.B. Karavashkin

In Fig. 2.23 we can see, how neutral hydrogen is distributed in our Galaxy; it is more concentrated along the arms. Shklovsky marks, clouds of ionised hydrogen belong also to the arms [1, p. 48]. Interestingly that not so long ago it was thought that magnetic lines of force follow the galaxy clouds that consist of ionised and so electro-conductive particles [1, p. 42], but this is, of course, too artificial supposition. In fact the clouds are, undoubtedly, formed by the force lines and adhere to them.

Fig. 2.23. Distribution of neutral hydrogen in the Galaxy. C marks the nucleus of Galaxy, and S marks the Sun [5, p. 115]

In Fig. 2.24 we show the globular cluster NGC 6782 whose arms are in the beginning of their formation. The negative of this image reveals that the galaxy in short time becomes elliptically shaped. The authors of this image write on their web page "Hubble Reveals Ultraviolet Galactic Ring": "The inner ring surrounds a small central bulge and a bar of stars, dust, and gas. This ring is itself part of a larger dim bar that ends in these two outer spiral arms."

a                                                                                  b

Fig. 2.24. Galaxy NGC 6782 - the globular cluster with the arms that began to form (a); the same image in negative (b) shows the real size of this galaxy and its periphery which is already transformed by the arms. "NGC 6782 is a relatively nearby galaxy, residing about 183 million light-years from Earth." http://heritage.stsci.edu/gallery

In the page supplemental to the principal caption related to this galaxy, the authors try to answer some basic questions of the same series as we are considering here: "1) What is known about how or whether the bars affect star formation in the ring? 2) What is it about the bar that would have the effect you describe above? 3) Why are the bars there in the first place? Why doesn't the material in the bars spread out into a spiral pattern like the rest of the galaxy?"

Taking into account what we said above, we can explain the multi-layered structure of this (and any other) galaxy so. Immediately around the nucleus in Fig. 2.24, we see the origin of arms and the very beginning of accumulation of peripheral gas and dust in them; the envelope of galaxy is still mainly distributed in the space around the nucleus; only small part of peripheral mass was already accumulated in the arms. Due to this fact, we see the inner contour of substance accumulated in arms, where star formation occurs, so this substance differs from other periphery; next we see still unconcentrated dim substance of periphery, it occupies an impressive area and still is very well seen; then we see the thermoinsulating vacuum interlayer - the same as we described for a star, it is caused by the ion circulation in the envelope; and finally we see the outer contour, in which electrons and negatively charged ions circulate - this is the electron cocoon of galaxy, also fully similar to that of star. The substance in these layers was structured by the electric field which imposes its affection onto the substance distribution, though the we can follow the arms up to the outer boundary of galaxy. But stars are formed still only in the part of arms close to the nucleus, where the density of substance is very high (because of it, in adult galaxies we see older stars around the nucleus), since the galactic processes in this system still did not gain full power. With the evolution, the substance of peripheral nebula will concentrate in the arms which would become bolder and sharper on the background of more 'cleaned' space, arms will become larger, so the star formation regions will grow.

a                                                                                       b

Fig. 2.25. The galaxy NGC 6782 in the ultraviolet spectrum (a) and the model of its structure (b) developed by its researchers [16]. NASA and The Hubble Heritage Team (STScI/AURA); acknowledgement: R. Windhorst (ASU). Illustration Credit: L. Frattare (STScI). Copied on http://heritage.stsci.edu/gallery

The authors of these images write also, "NGC 6782 is a relatively nearby galaxy, residing about 183 million light-years from Earth. The light from galaxies at much larger distances is stretched to longer, redder wavelengths ["redshifted"], due to the expansion of the universe. This means that if astronomers want to compare visible-light images of very distant galaxies with galaxies in our own neighborhood, they should use ultraviolet images of the nearby ones. Astronomers find that the distant galaxies tend to have different structures than nearby ones, even when they use the correct procedure of comparing visible light in distant galaxies with ultraviolet light from nearby ones" [16]. In this connection we would recall a commonly known fact that the ultraviolet light is considerably absorbed by space medium, so ultraviolet images of far galaxies loss many details, and the result much differs from such images of near galaxies, of course.