Radiation of magnetoacoustic waves in the interstellar medium by physical variable stars

Dokuchaev, V. P.

doi:10.1134/1.1558156

Cited by 5 publications

(10 citation statements)

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“…Originally described by Chandrasekhar for a collisionless medium [1], this effect has also been examined in gaseous media. Steady state solutions, where a constant-velocity perturber of mass M moves through an infinite homogeneous gas have shown the dynamical friction to be [2][3][4][5]…”

Section: Jcap10(2019)074mentioning

confidence: 99%

“…For superfluids at zero temperature, on the other hand, there are indeed only longitudinal dynamical low energy excitations due to absolute degeneracy of the constituents. 2 Although the above-mentioned hydrodynamic approach to dynamical friction is applicable to superfluids in certain limiting cases, in general it is plagued with puzzles. For instance, as it stands (1.1) has an unphysical c s → 0 limit.…”

Section: Jcap10(2019)074mentioning

confidence: 99%

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Dynamical friction in superfluids

Berezhiani

Elder

Khoury

2019

J. Cosmol. Astropart. Phys.

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We compute the dynamical friction on a small perturber moving through an inviscid fluid, i.e., a superfluid. Crucially, we account for the tachyonic gravitational mass for sound waves, reminiscent of the Jeans instability of the fluid, which results in non-zero dynamical friction even for subsonic velocities. Moreover, we illustrate that the standard leading order effective theory in the derivative expansion is in general inadequate for analysing supersonic processes. We show this in two ways: (i) with a fluid treatment, where we solve the linearized hydrodynamical equations coupled to Newtonian gravity; and (ii) with a quasiparticle description, where we study the energy dissipation of a moving perturber due to phonon radiation. Ordinarily a subsonic perturber moving through a superfluid is kinematically prohibited from losing energy, however the Jeans instability modifies the dispersion relation of the fluid which can result in a small but non-vanishing dynamical friction force. We also analyse the soft phonon bremsstrahlung by a subsonic perturber scattered off an external field.

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Section: Jcap10(2019)074mentioning

confidence: 99%

Section: Jcap10(2019)074mentioning

confidence: 99%

Dynamical friction in superfluids

Berezhiani

Elder

Khoury

2019

J. Cosmol. Astropart. Phys.

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“…With such an accretion rate, the Sgr A* BH could have grown to its present mass over the galaxy lifetime. The SMBH evolution in galactic centers due to tidal disruption of stars and dark matter accretion has been studied for many years (also see, e. g., [86][87][88]). Although BHs in galactic centers are small in size, their powerful gravitational field can affect giant structures and processes on galactic scales and beyond.…”

Section: Observational Appearances Of the Central Galactic Blackmentioning

confidence: 99%

“…For E < E cr , the distribution function of finite stars in the gravitational field of a BH can be approximated as [78][79][80][81]88] f (E,…”

Section: Distribution Of Stars In the Galactic Centermentioning

confidence: 99%

“…The SMBH in the Galactic center is 'dormant' because of a low rate of tidal disruption of stars and a small accretion rate of the ambient gas. The rate of tidal disruption of stars by a Ṅfin , under the condition r cr < r h (see formula (3) in Section 4) can be represented in the form [78][79][80][81] Ṁh ≃ 2, 7…”

Section: Observational Appearances Of the Central Galactic Black Holementioning

confidence: 99%

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Physical laboratory at the center of the Galaxy

Dokuchaev

Eroshenko

2015

Phys.-Usp.

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We review the physical processes that occur at the center of the Galaxy and that are related to the supermassive black hole Sgr A* residing there. The discovery of high-velocity S0 stars orbiting Sgr A* for the first time allowed measuring the mass of this supermassive black hole, the closest one to us, with a 10\% accuracy, with the result $M_h=(4.1\pm0.4)\times 10^6M_\odot$. Further monitoring can potentially discover the Newtonian precession of the S0 star orbits in the gravitational field of the black hole due to invisible distributed matter. This will yield the "weight" of the elusive dark matter concentrated there and provide new information for the identification of dark matter particles. The weak accretion activity of the "dormant quasar" at the Galactic center occasionally shows up as quasiperiodic X-ray and near-IR oscillations with mean periods of $11$ and $19$ min. These oscillations can possibly be interpreted as related to the rotation frequency of the Sgr A* event horizon and to the latitude oscillations of hot plasma spots in the accretion disk. Both these frequencies depend only on the black hole gravitational field and not on the accretion model. Using this interpretation yields quite the accurate values for both the mass $M_h$ and the spin $a$ (Kerr rotation parameter) of Sgr A*: $M_h=(4.2\pm0.2)\times 10^6M_\odot$ and $a=0.65\pm0.05$.Comment: Review paper, 16 pages, 9 figure

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Simulations of common-envelope evolution in binary stellar systems: physical models and numerical techniques

Roepke

Marco

2023

Living Rev Comput Astrophys

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When the primary star in a close binary system evolves into a giant and engulfs its companion, its core and the companion temporarily orbit each other inside a common envelope. Drag forces transfer orbital energy and angular momentum to the envelope material. Depending on the efficiency of this process, the envelope may be ejected leaving behind a tight remnant binary system of two stellar cores, or the cores merge retaining part of the envelope material. The exact outcome of common-envelope evolution is critical for in the formation of X-ray binaries, supernova progenitors, the progenitors of compact-object mergers that emit detectable gravitational waves, and many other objects of fundamental astrophysical relevance. The wide ranges of spatial and temporal timescales that characterize common-envelope interactions and the lack of spatial symmetries present a substantial challenge to generating consistent models. Therefore, these critical phases are one of the largest sources for uncertainty in classical treatments of binary stellar evolution. Three-dimensional hydrodynamic simulations of at least part of the common-envelope interaction are the key to gain predictive power in modeling common-envelope evolution. We review the development of theoretical concepts and numerical approaches for such three-dimensional hydrodynamic simulations. The inherent multi-physics, multi-scale challenges have resulted in a wide variety of approximations and numerical techniques to be exercised on the problem. We summarize the simulations published to date and their main results. Given the recent rapid progress, a sound understanding of the physics of common-envelope interactions is within reach and thus there is hope that one of the remaining fundamental problems of stellar astrophysics may be solved before long.

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Radiation of magnetoacoustic waves in the interstellar medium by physical variable stars

Cited by 5 publications

References 1 publication

Dynamical friction in superfluids

Dynamical friction in superfluids

Physical laboratory at the center of the Galaxy

Simulations of common-envelope evolution in binary stellar systems: physical models and numerical techniques

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