Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum
Spiral galaxies are spinning, internally densified objects. The Virial Theorem explains galactic rotation curves via its linkage of the rotation rate to the gravitational self-potential (<i>U<sub>g</sub></i>) and the moment of inertia of oblate spheroids. We devise a new anal...
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| Format: | Article |
| Language: | English |
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MDPI AG
2018-11-01
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| Series: | Galaxies |
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| Online Access: | https://www.mdpi.com/2075-4434/6/4/115 |
| _version_ | 1828412767224201216 |
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| author | Robert E. Criss Anne M. Hofmeister |
| author_facet | Robert E. Criss Anne M. Hofmeister |
| author_sort | Robert E. Criss |
| collection | DOAJ |
| description | Spiral galaxies are spinning, internally densified objects. The Virial Theorem explains galactic rotation curves via its linkage of the rotation rate to the gravitational self-potential (<i>U<sub>g</sub></i>) and the moment of inertia of oblate spheroids. We devise a new analytical solution that allows galactic mass and volumetric density (kg m<sup>−3</sup>) profiles to be extracted from velocity and its derivative as functions of equatorial radius. This inverse model of rotation curves is direct, unambiguous, and parameter-free. To probe galactic evolution, we combine energy minimization, angular momentum conservation, and the Virial Theorem. The characteristic flat shape of spiral galaxies results from an initial vertical collapse of a spinning, colossal molecular cloud, which reduces <i>U<sub>g</sub></i> while conserving angular momentum. Subsequent inward densification further lowers <i>U<sub>g</sub></i>, producing bulges, but conserving angular momentum requires mass loss, achieved by the outward movement of the distal parts of the spiral arms. Many of the evolutionary patterns of spiral galaxies are exhibited by the changing shapes of hurricanes during formation and dissipation. In contrast, elliptical galaxies evolve from a cloud with roughly random orbits into progressively rounder, internally denser objects, with angular momentum conserved by the development of vertically oriented jets. Galactic evolution is governed by the initial inventory of mass and angular momentum, resulting in separate paths for elliptical and spiral galaxies, as is codified in Hubble’s tuning fork diagram. |
| first_indexed | 2024-12-10T12:55:14Z |
| format | Article |
| id | doaj.art-ca17b3af15204a5aa3caf830ad538fcb |
| institution | Directory Open Access Journal |
| issn | 2075-4434 |
| language | English |
| last_indexed | 2024-12-10T12:55:14Z |
| publishDate | 2018-11-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Galaxies |
| spelling | doaj.art-ca17b3af15204a5aa3caf830ad538fcb2022-12-22T01:48:07ZengMDPI AGGalaxies2075-44342018-11-016411510.3390/galaxies6040115galaxies6040115Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular MomentumRobert E. Criss0Anne M. Hofmeister1Department of Earth and Planetary Science, Washington University, St. Louis, MO 63130, USADepartment of Earth and Planetary Science, Washington University, St. Louis, MO 63130, USASpiral galaxies are spinning, internally densified objects. The Virial Theorem explains galactic rotation curves via its linkage of the rotation rate to the gravitational self-potential (<i>U<sub>g</sub></i>) and the moment of inertia of oblate spheroids. We devise a new analytical solution that allows galactic mass and volumetric density (kg m<sup>−3</sup>) profiles to be extracted from velocity and its derivative as functions of equatorial radius. This inverse model of rotation curves is direct, unambiguous, and parameter-free. To probe galactic evolution, we combine energy minimization, angular momentum conservation, and the Virial Theorem. The characteristic flat shape of spiral galaxies results from an initial vertical collapse of a spinning, colossal molecular cloud, which reduces <i>U<sub>g</sub></i> while conserving angular momentum. Subsequent inward densification further lowers <i>U<sub>g</sub></i>, producing bulges, but conserving angular momentum requires mass loss, achieved by the outward movement of the distal parts of the spiral arms. Many of the evolutionary patterns of spiral galaxies are exhibited by the changing shapes of hurricanes during formation and dissipation. In contrast, elliptical galaxies evolve from a cloud with roughly random orbits into progressively rounder, internally denser objects, with angular momentum conserved by the development of vertically oriented jets. Galactic evolution is governed by the initial inventory of mass and angular momentum, resulting in separate paths for elliptical and spiral galaxies, as is codified in Hubble’s tuning fork diagram.https://www.mdpi.com/2075-4434/6/4/115inverse modelsrotation curvesevolutionangular momentumdissipationspiral galaxieselliptical galaxies |
| spellingShingle | Robert E. Criss Anne M. Hofmeister Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum Galaxies inverse models rotation curves evolution angular momentum dissipation spiral galaxies elliptical galaxies |
| title | Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum |
| title_full | Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum |
| title_fullStr | Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum |
| title_full_unstemmed | Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum |
| title_short | Galactic Density and Evolution Based on the Virial Theorem, Energy Minimization, and Conservation of Angular Momentum |
| title_sort | galactic density and evolution based on the virial theorem energy minimization and conservation of angular momentum |
| topic | inverse models rotation curves evolution angular momentum dissipation spiral galaxies elliptical galaxies |
| url | https://www.mdpi.com/2075-4434/6/4/115 |
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