TFNR - Cosmic objects and bodies
In the common use, in astronomy, the two terms object and body are often used indifferently. Astronomical or celestial bodies are single, compact physical entities. Astronomical object are complex, more structured physical entities, which can consist of many parts, objects, bodies.
While Cosmic structures define more complex, structured and wide arrangements / organizations of interrelated parts, objects and bodies. Bodies and objects represent the components that make up the complex cosmic structures that fill the Universe.
In any case, let's give some examples of the objects, bodies that populate the cosmos:
- small aggregates of dust and frozen substances
- small to medium rocks
- asteroids
- comets with their tails
- moons and satellites
- planetoids
- planets
- stars of various types and in different phases of their evolution (various populations and evolutive paths)
- planetary systems
- star clusters and filaments
- nebulae
- galaxies
Planetary systems, star clusters, nebulae, galaxies as well as objects can be also considered astronomical structures, bridges between stellar bodies and their planetary systems and large cosmic structures (groups and clusters of galaxies, superclusters, the cosmic web, etc.).
Let's examine in greater detail galaxies, the most complex and vast objects that we have listed here.
Black Holes
Galaxies
Generally a galaxy is described as a system of stars, stellar remnants, interstellar gas, dust and dark matter bound together by gravity. The order in which the supposed constituents of galaxies are listed says a lot about the current consolidated knowledge regarding the nature, structure and dynamics of these fascinating celestial objects, the true cosmic building blocks. Lastly, dark matter is almost considered a necessary evil to account for the bizarre dynamics of visible matter. In particular, we talk about the differences between expected and observed values in the curve of the speed of rotation of the material in relation to the distance from the center in disk galaxies.
Although difficult to accept, to understand the nature, structure, origin and dynamics of these celestial objects we must recognize the central role played by dark matter and, given the hypotheses we have formulated regarding it, also dark energy.
We must think of a galaxy as a complex system, formed by a rotating bubble, internally constituted by dark matter and by a boundary of dark energy, and, normally but not necessarily, by ordinary matter of various kinds, all characterized by a variously turbulent dynamics, with ordinary matter and energy entering and exiting (em radiation, particles, gas, dust, stellar bodies, black holes, etc.).
Dark matter and energy, absolutely related components, two aspects of the same "substance", are therefore not only the main component in terms of quantity, mass, but are the most important elements for the structure and dynamics of a galaxy. Without DM and DE the existence of a galactic bubble is not possible.
In cases where, due to a collision between two galactic bubbles, the greater inertia of ordinary matter has determined its exit from the DM/DE bubble, we can observe on one side an empty or partially empty dark galactic bubble. And next to it, we could observe a galaxy (the visible component) without dark matter (with consequent alteration of the shape and rotation speed curve on a "cosmic" time scale obviously).
Galaxies can have various extensions (dwarf, normal size, extralarge) and shapes: regular (spiro, elliptical), irregular (colliding / merging galaxies), strange shaped galaxies, etc.
These highly structured objects are more than collections, aggregates of gas, dust, rocks, stars, planets, etc.
In fact, their visible part, made up of ordinary matter and radiation, represents only a small part of these cosmic objects. The most extensive, massive and relevant part for its overall structure and dynamics is what we call "dark".
Let's take a look at the structure of a typical galaxy.
... surrounding small dwarf galaxies ...
And now, a look at its dynamics and the dynamics of the constituent parts of the galactic system.
Links to the tables of contents of TFNR Paper
