Galaxies, colliding

Neutrinos can be cold dark matter if their masses are around few GeV or a TeV. However, fourth-generation heavy neutrinos lighter than 45 GeV are excluded by the measurement of the Z-boson decay width at the Large Electron-Positron collider at CERN. Moreover, direct searches for WIMP dark matter in our galaxy exclude Dirac neutrinos heavier than 0.5 GeV as the dominant component of the galactic dark halo (see Figure 3). Thus although heavy Dirac neutrinos could still be a tiny part of the halo dark matter, they cannot solve the cold dark matter problem. 

All the particles mentioned have their anti-particles (designated by a bar above the particle symbol), except the photon and the mesons, who are their own antiparticles. We may think about antimatter as consisting of antiprotons and antineutrons in an antinucleus surrounded by antielectrons (i.e. positrons). Superficially, there would be no way to distinguish such antimatter from our matter (sometimes called koino matter). It has been proposed that the universe is made up of matter and antimatter as a requirement of the principle of symmetry. In that case some galaxies, which perhaps can be observed, should be made up of antimatter. When such antimatter galaxies (or material expelled fi-om them) collide with koino matter galaxies, both types of matter are annihilated and tremendous amounts of energy released. 

The origin of X-rays, 7-ray bursts and radiowaves that pervade the Galaxy is as mysterious as the cosmic-ray sources. Evidence is mounting that in most cases these phenomena are linked to violent explosions, thought to include neutron-star quakes, quark nuggets, supernovae, matter-antimatter annihilation, clumping of quasars and colliding stars. Of all space radiations radio phenomena have been studied in most detail. 

In view of modern observations Godel s concerns appear less serious. Galaxies are now known to wander and even collide. There is hardly any reason why not to explore the alternative possibility. 

Fig. 12 Examples of two colliding galaxies (a) Material flowing between two battered galaxies that bumped into each other about 100 million years ago. (b) The cores of the twin galaxies are the orange blobs (Photographs NGC 5426/5427 and NGC 4038/4039, taken by the Hubble telescope, from http //hubblesite.org/newsdesk/archive/releases/...

The most distant of the three objects (D = 100 Mpc), NGC 6240 exhibits a double nuclei in radio and visible and a very strong H2 peak between the nuclei indicating a shock at the interface of the colliding galaxies. The 3.3 pm image is dose to the radio or [Fe H] maps and confirms that both nudei are star-forming. The Line/Continuum map (Fig. 3) shows i) depletion of PAH at both peaks i) depletion of PAH at ESE perpendicular to the nudeus-nudeus axis exactly where a superwind was evidenced (Heckman, Armus Miley, 1990) Hi) a maximum at WSW, where CO emission peaks (Wang, ScoviUe Sanders, 1991). 

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