Heat in a Galaxy
Does a Galaxy hold heat? Do its stars hold heat in their motion?
A definition of temperature:
Roughly, the temperature of a body at rest is a measure of the mean of the energy of the translational, vibrational and rotational motions of matter's particle constituents, such as molecules, atoms, and subatomic particles. The full variety of these kinetic motions, along with potential energies of particles, and also occasionally certain other types of particle energy in equilibrium with these, make up the total internal energy of a substance. Internal energy is loosely called the heat energy or thermal energy in conditions when no work is done upon the substance by its surroundings, or by the substance upon the surroundings. Internal energy may be stored in a number of ways within a substance, each way constituting a "degree of freedom". At equilibrium, each degree of freedom will have on average the same energy<...> . It may be said that, for most situations, the thermodynamic temperature is specified by the average translational kinetic energy of the particles.
The mechanisms include conduction, through direct contact of immobile bodies, or through a wall or barrier that is impermeable to matter; or radiation between separated bodies; or isochoric mechanical work done by the surroundings on the system of interest. When there is a suitable path between two systems with different temperatures, heat transfer occurs necessarily, immediately, and spontaneously from the hotter to the colder system. Thermal conduction occurs by the stochastic (random) motion of microscopic particles (such as atoms or molecules).
Heat transfer is usually between bodies or distinct particles. The kinetic energy of particles can be used to quantify a temperature of a gas, or the heat being held.
Can stars be treated as distinct particles that hold heat? Can a galaxy hold heat in the motion of its stars? Are galaxies with more stars hotter?
This usage is beyond my understanding of thermodynamics.
The attached abstract reveals a new application of 'heat' in a galaxy.
EXCITATION OF COUPLED STELLAR MOTIONS IN THE GALACTIC DISK BY ORBITING SATELLITES
From the abstract:
We use a set of high-resolution N-body simulations of the Galactic disk to study its interactions with the population of cosmologically predicted [galaxy] satellites. One simulation illustrates that multiple passages of massive satellites with different velocities through the disk generate a wobble. They also produce flares in the outer disk parts and gradually heat the disk through bending waves. [Another] experiment shows that an individual satellite as massive as the Sagittarius dwarf galaxy passing through the disk will drive coupled horizontal and vertical oscillations of stars in underdense regions with small associated heating. This experiment shows that vertical excursions of stars in these low-density regions can exceed 1 kpc in the Solar neighborhood, resembling the recently locally detected coherent vertical oscillations. They can also induce non-zero vertical streaming motions as large as 10–20 km/s, which is consistent with recent observations in the Galactic disk. This phenomenon appears as a local ring with modest associated disk heating.
Apparently 'non-zero vertical streaming motions' are observed in the Galactic disk, in our local 'underdense' region.
I disagree with an explanation using the term 'heat' for changes in orbits of stars.
I welcome comments about 'modest disk heating' in our region of the Milky Way.
Is there 'heat' present in the galactic disk? Do the spiral arms rotate by their temperature?
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