Galaxies nuclei

I then discuss the evidence from AGN for the existence of supermassive black holes in galaxy nuclei, as well as evidence for such black holes in ordinary galaxy nuclei. I use the free motion of gas parcels to illustrate aspects of accretion disks around black holes, showing how to calculate energy efficiency and surface emissivity of disks, and the rate of black hole spin-up. I recall the primary methods for black hole mass determination, the correlation of black hole mass with the stellar velocity dispersion of its neighborhood, and implications for the origin of supermassive black holes. Finally, I consider the formation of primordial black holes, and calculation of their mass spectrum at present in the case of scale invariant primordial inhomogeneities. 

Hoyle, F. (1965). Galaxies, Nuclei, and Quasars. London Heinemann. 

Henderson, L. J. (1917). The Order of Nature. Cambridge, MA Harvard University Press. Holm, L. and Sander, C. (1996). Mapping the protein universe. Science, 273, 595-603. Hoyle, F. (1964). Galaxies, Nuclei and Quasars. New York, NY Harper and Row. 

Figure 9. Top The correlation of spiral galaxy abundance (O/H) at the half-light radius of disk from the galaxy nucleus vs. galaxy blue luminosity. Bottom abundance versus maximum rotational speed Vrot-...

It is known that the oxygen abundance in the interstellar medium increases all the time this nucleus is produced by type 11 supernovas which, one after the other, also contribute their iron production to the Galaxy (Fig. 8.7). The pO mechanism is thus likely to grow in importance as the Galaxy evolves. In other words, clues to the Op mechanism should be sought in the early phases of galactic evolution, that is, in halo stars. The fact remains that the two mechanisms induce different evolution in beryllium and boron as a function of oxygen. 

The Caabundance has been studied in stars by optical spectra. Because 40 Ca dominates the spectra of Ca in stars, and especially because 4°Ca is a primary alpha nucleus, the galactic evolution of 4°Ca is the same as the observed galactic evolution of calcium elemental abundance. As nucleosynthesis progressed in the galaxy the Ca/H abundance... 

The nucleus of the galaxy is surrounded by a nuclear bulge that is 12,000 light years in diameter and... 

What is in the nucleus of the Milky Way If we look with optical telescopes, we see nothing. The interstellar dust obscures the optical light. The center of the Milky Way does, however contain very strong sources of radio waves, infrared light, and x rays. One such source, called Sagittarius A", appears to lie at the precise center of the galaxy, the point about which the entire system rotates. 

Globular cluster—A cluster of roughly 100,000 older stars in a compact spherical distribution. Halo— A spherical distribution of older stars and clusters of stars surrounding the nucleus and disk of our galaxy. 

Milky Way—The galaxy in which we are located. Nucleus—The central core of a galaxy. 

Spiral galaxy—A galaxy in which spiral arms wind outward from the nucleus. 

In the stars of this galaxy, four hydrogen nuclei fuse to form a single He nucleus. 

Since the density in the disk of the galaxy is of order one particle per cm3 and the typical partial cross section for a light nucleus will be of order 100 mb, the scale for the characteristic time is 107 years. The full analysis requires self-consistent solution of the coupled equations for all species accounting for all loss terms, as described in John Wefel s lecture in this volume (Wefel, 2005). A nice overview of propagation models is given by Jones et al., 2001. 

Figure 7. Warm dust emission in early-type galaxies. Six galaxies are shown, each with separate images in stellar emission (3.6 /um) and warm dust emission (8.0 pm non-stellar ). The top three galaxies are classified as ellipticals and show no sign of warm dust emission at 8.0 pm. The bottom three galaxies are classified as lenticulars and show resolved warm dust. NGC 4203 appears face-on with several spiral arms emanating out from its nucleus, NGC 5363 appears somewhat inclined and shows two arms, and NGC 1023 shows a smooth distribution of dust.

Limited nucleosynthesis occurs outside stars in gas exposed to very energetic particles. One such site is the interstellar medium of a galaxy permeated by cosmic rays. High-energy collisions between a nucleus among the cosmic rays and one in the interstellar... 

Spectropolarimetry has proven to be an important tool in the development of unified theories of active galactic nuclei (AGN). Its strength is that it provides an alternative view of the inner regions of the active nucleus. This allows for the study the stracture and kinematics of both polarizing materials and the emission source. Examples of polarization spectra of two active galaxies NGC 5548 and Was 45 are given in Fig. 15. The observations of NGC 5548 were made in 1997 and Was 45 in 1999 with the 1.2m William Hershel Telescope. 

A notable feature of the spiral structures is the lack of a heavy core as seen in spiral galaxies, such as M51, shown in Plate 5.1. A reasonable explanation of this and of the uniform alignment and chirality of the spirals is that they originate in turbulent flow firom a central point, and therefore seen oriented in the same radial projection. In hydrodynamics such structures are known as vortices or eddies. Each of the eddies generated by the turbulent expansion is the potential nucleus of a new galaxy. 

The exact nature of quasars is unknown but it is believed that they are the nuclei of galaxies in which there is violent activity. The luminosity of the nucleus is so much greater than that of the rest of the galaxy that the source appears pointlike, it has been proposed that the power source in a quasar is a supermassive black hole accreting material from the stars and gas in the surrounding galaxy. 

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