The Principle of Maximum Entropy and the Distribution of Mass in Galaxies
We do not have a final answer to the question of <i>why galaxies choose a particular internal mass distribution.</i> Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two...
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| Format: | Article |
| Language: | English |
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MDPI AG
2022-03-01
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| Series: | Universe |
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| Online Access: | https://www.mdpi.com/2218-1997/8/4/214 |
| _version_ | 1797434170219167744 |
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| author | Jorge Sánchez Almeida |
| author_facet | Jorge Sánchez Almeida |
| author_sort | Jorge Sánchez Almeida |
| collection | DOAJ |
| description | We do not have a final answer to the question of <i>why galaxies choose a particular internal mass distribution.</i> Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time, and the fact that the mass distribution maximizing the classical Boltzmann–Gibbs entropy is unphysical. These arguments are questionable. In particular, when the Tsallis entropy that describes self-gravitating systems is used to define TE, the mass distributions that result (i.e., the polytropes) are physically sensible. This work spells out this and other arguments for TE and presents the polytropes and their properties. It puts forward empirical evidence for the mass distribution observed in galaxies to be consistent with polytropes. It compares polytropes with Sérsic functions and it shows how the DM halos resulting from cosmological numerical simulations become polytropes when efficient collisions are allowed. It also discusses pathways to thermalization bypassing two-body collisions. It finally outlines future developments including deciphering whether or not DM particles collide efficiently. |
| first_indexed | 2024-03-09T10:28:22Z |
| format | Article |
| id | doaj.art-9538e7b86ac841748f01d09c151adb52 |
| institution | Directory Open Access Journal |
| issn | 2218-1997 |
| language | English |
| last_indexed | 2024-03-09T10:28:22Z |
| publishDate | 2022-03-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Universe |
| spelling | doaj.art-9538e7b86ac841748f01d09c151adb522023-12-01T21:29:55ZengMDPI AGUniverse2218-19972022-03-018421410.3390/universe8040214The Principle of Maximum Entropy and the Distribution of Mass in GalaxiesJorge Sánchez Almeida0Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, SpainWe do not have a final answer to the question of <i>why galaxies choose a particular internal mass distribution.</i> Here we examine whether the distribution is set by thermodynamic equilibrium (TE). Traditionally, TE is discarded for a number of reasons including the inefficiency of two-body collisions to thermalize the mass distribution in a Hubble time, and the fact that the mass distribution maximizing the classical Boltzmann–Gibbs entropy is unphysical. These arguments are questionable. In particular, when the Tsallis entropy that describes self-gravitating systems is used to define TE, the mass distributions that result (i.e., the polytropes) are physically sensible. This work spells out this and other arguments for TE and presents the polytropes and their properties. It puts forward empirical evidence for the mass distribution observed in galaxies to be consistent with polytropes. It compares polytropes with Sérsic functions and it shows how the DM halos resulting from cosmological numerical simulations become polytropes when efficient collisions are allowed. It also discusses pathways to thermalization bypassing two-body collisions. It finally outlines future developments including deciphering whether or not DM particles collide efficiently.https://www.mdpi.com/2218-1997/8/4/214Tsallis entropygalaxy structurepolytropesSérsic functionsNFW profilesdark matter cores |
| spellingShingle | Jorge Sánchez Almeida The Principle of Maximum Entropy and the Distribution of Mass in Galaxies Universe Tsallis entropy galaxy structure polytropes Sérsic functions NFW profiles dark matter cores |
| title | The Principle of Maximum Entropy and the Distribution of Mass in Galaxies |
| title_full | The Principle of Maximum Entropy and the Distribution of Mass in Galaxies |
| title_fullStr | The Principle of Maximum Entropy and the Distribution of Mass in Galaxies |
| title_full_unstemmed | The Principle of Maximum Entropy and the Distribution of Mass in Galaxies |
| title_short | The Principle of Maximum Entropy and the Distribution of Mass in Galaxies |
| title_sort | principle of maximum entropy and the distribution of mass in galaxies |
| topic | Tsallis entropy galaxy structure polytropes Sérsic functions NFW profiles dark matter cores |
| url | https://www.mdpi.com/2218-1997/8/4/214 |
| work_keys_str_mv | AT jorgesanchezalmeida theprincipleofmaximumentropyandthedistributionofmassingalaxies AT jorgesanchezalmeida principleofmaximumentropyandthedistributionofmassingalaxies |