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1

Supernowe czarnych karłów

Osarczuk Janusz

Postępy Fizyki

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2023

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T. 74, z. 3

24--26

PL

Białe karły nie są ostatnim stadium ewolucji gwiazd mało- lub średnio masywnych. Kiedyś wypromieniują całe swoje zapasy energii i stając się zimnymi i ciemnymi ciałami, zamienią się w czarne karły. Nie oznacza to jednak, że przestaną być interesującymi obiektami.

EN

White dwarfs are not the final stage in the evolution of low- or medium-mass stars. One day they will radiate all their energy reserves and become cold and dark bodies, they will turn into black dwarfs. However, it does not mean that they will stop being interesting objects.

2

Superspinning Quark Stars Limited by Twin High-Frequency Quasiperiodic Oscillations

Stuchlìk Z., Schee J., Šràmkovà E., Török G.

Acta Astronomica

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2017

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Vol. 67, No. 2

181--201

EN

We study properties of Keplerian disks and their high-frequency quasi-periodic oscillations (HF QPOs) in the field of quark stars with dimensionless spin a breaking the black-hole spin limit of a=1 up to a≈1.3. Using the external geometry of the superspinning quark stars approximated by the Kerr geometry, we show that the Keplerian disks have to touch the surface of such quark stars and their accretion efficiency η≈18% significantly exceeds the efficiency related to the Schwarzschild black holes. Using the geodesic oscillation models, we test possible existence of the superspinning quark stars in atoll sources demonstrating the twin HF QPOs with resonant frequency ratios 3:2, 4:3, 5:4. For explanation of the twin HF QPOs we consider the standard relativistic precession model and its modifications, the tidal distortion model, the resonance epicyclic and the warped disk model. In a given model, we assume occurrence of the twin oscillatory modes at a common resonant dimensionless radius x=r/M determined by the frequency ratio and the quark star spin a. The theoretical limit R>3M on the quark star surface radius puts strong restrictions on the relations between the resonant radii x and the quark star spin a. These restrictions imply that all the considered geodesic oscillation models can be excluded, except for one variant of the relativistic precession model, or alternatively the tidal distortion and warped disk models, that allow for appearance of the twin HF QPOs with frequency ratio 3:2 at radii slightly above the theoretical limit on the radius of the quark star surface, but exclude the smaller frequency ratios (4:3, 5:4).

3

Observational Tests of Neutron Star Relativistic Mean Field Equations of State

Urbanec M., Beták E., Stuchlík Z.

Acta Astronomica

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2010

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Vol. 60, No. 2

149--163

EN

Set of neutron star observational results is used to test some selected equations of state of dense nuclear matter. The first observational result comes from the mass-baryon number relation for pulsar B of the double pulsar system J0737-3039. The second one is based on the mass-radius relation coming from observation of the thermal radiation of the neutron star RX J1856.35-3754. The third one follows the population analysis of isolated neutron star thermal radiation sources. The last one is the test of maximum mass. The equation of state of asymmetric nuclear matter is given by the parametrized form of the relativistic Brueckner-Hartree-Fock mean field, and we test selected parametrization that represent fits of full relativistic mean field calculation. We show that only one of them is capable to pass the observational tests. This equation of state represents the first equation of state that is able to explain all the mentioned observational tests, especially the very accurate test given by the double pulsar even if no mass loss is assumed.

4

Binary Coalescence of a Strange Star with a Black Hole: Newtonian Results

Lee W. H., Kluźniak W., Nix J.

Acta Astronomica

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2001

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Vol. 51, No. 4

331--346

EN

We present Newtonian three-dimensional hydrodynamical simulations of the merger of quark stars with black holes. The initial conditions correspond to non-spinning stars in Keplerian orbits, the code includes gravitational radiation reaction in the quadrupole approximation for point masses. We find that the quark star is disrupted, forming transient accretion structures around the black hole, but 0.03 of the original stellar mass survives the initial encounter and remains in an elongated orbit as a rapidly rotating quark starlet, in all cases. No resolvable amount of mass is dynamically ejected during the encounters - the black hole eventually accretes 99.99%±0.01% of the quark matter initially present.