7. Galaxies

2016 ◽  
pp. 115-144
Author(s):  
James Binney
Keyword(s):  
Dark Matter ◽  
Gravitational Field ◽  
Chemical Evolution ◽  
Spiral Galaxies ◽  
Stellar Dynamics ◽  
Huge Number ◽  
Lenticular Galaxies ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies ◽  
Intermediate Density

‘Galaxies’ describes galaxy morphology, the chemical evolution of galaxies, and stellar dynamics. A galaxy consists of a huge number of point masses—stars and dark matter—that move freely in the gravitational field that they jointly generate. The nature of a galaxy is largely determined by its luminosity, its bulge-to-disc ratio, and the ratio of its mass of cold gas to the mass in stars. Galaxies are also shaped by their environments. Dense environments are rich in elliptical and lenticular galaxies, while abnormally under-dense environments are rich in dwarf irregular galaxies. Spiral galaxies like our own tend to inhabit regions of intermediate density.

scholarly journals Gravitoelectromagnetism and stellar orbits in galaxies

2021 ◽  
pp. 2150102
Author(s):  
Viktor T. Toth
Keyword(s):  
General Relativity ◽  
Dark Matter ◽  
Gravitational Field ◽  
Magnetic Force ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Observable Effect ◽  
Stellar Orbits ◽  
Gravitational Fields ◽  
The Impact

Beyond the Newtonian approximation, gravitational fields in general relativity can be described using a formalism known as gravitoelectromagnetism. In this formalism, a vector potential, the gravitomagnetic potential, arises as a result of moving masses, in strong analogy with the magnetic force due to moving charges in Maxwell’s theory. Gravitomagnetism can affect orbits in the gravitational field of a massive, rotating body. This raises the possibility that gravitomagnetism may serve as the dominant physics behind the anomalous rotation curves of spiral galaxies, eliminating the need for dark matter. In this essay, we methodically work out the magnitude of the gravitomagnetic equivalent of the Lorentz force and apply the result to the Milky Way. We find that the resulting contribution is too small to produce an observable effect on these orbits. We also investigate the impact of cosmological boundary conditions on the result and find that these, too, are negligible.

scholarly journals 3D model of magnetic fields evolution in dwarf irregular galaxies

2010 ◽  
Vol 6 (S274) ◽  
pp. 389-392
Author(s):  
Hubert Siejkowski ◽  
Marian Soida ◽  
Katarzyna Otmianowska-Mazur ◽  
Michał Hanasz ◽  
Dominik J. Bomans
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Gravitational Potential ◽  
Spiral Galaxies ◽  
Cosmic Ray ◽  
Dynamo Model ◽  
Slow Rotation ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies ◽  
The Magnetic Field

AbstractRadio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.

scholarly journals Dark Matter search in dwarf irregular galaxies with the Fermi Large Area Telescope

2021 ◽  
Author(s):  
Viviana Gammaldi ◽  
Judit Pérez-Romero ◽  
Javier Coronado-Blázquez ◽  
Mattia Di Mauro ◽  
Miguel Angel Sánchez-Conde ◽  
...  
Keyword(s):  
Dark Matter ◽  
Large Area ◽  
Dark Matter Search ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies

The Various Kinematics of Dwarf Irregular Galaxies in Nearby Groups and Their Dark Matter Distributions

2000 ◽  
Vol 120 (6) ◽  
pp. 3027-3059 ◽  
Author(s):  
Stéphanie Côté ◽  
Claude Carignan ◽  
Kenneth C. Freeman
Keyword(s):  
Dark Matter ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies

scholarly journals Gas Mixing, Gas Cycles and the Chemical Evolution of Dwarf Irregular Galaxies

2004 ◽  
Vol 217 ◽  
pp. 178-187 ◽  
Author(s):  
Gerhard Hensler ◽  
Joachim Köppen ◽  
Jan Pflamm ◽  
Andreas Rieschick
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Chemical Evolution ◽  
Dwarf Galaxies ◽  
Type Ii ◽  
Gas Mixing ◽  
Active Star ◽  
Active Star Formation ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies

Dwarf galaxies are ideal laboratories to study influential effects on galaxy evolution. In particular, their gas-rich variant with very active star formation, starbursting dwarf irregulars, shows chemical and structural signatures that lead unambiguously to the conclusion that they are standing in a vital contact with their surroundings. Gas infall cannot only trigger star formation but also allows for a reduction of the metal content. on the other hand, active star formation ignites numerous supernovae type II which accumulate and can produce a galactic wind. This again depletes the metals pushing them into a gas mixing cycle with different timescales, locally of about 10 Myrs, but an galactic scales of at least 1 Gyr. This paper illuminates the different processes like gas infall and outflow and their effects on the chemical evolution, the star formation, and the gas mixing in dwarf irregular galaxies.

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