Dynamical stability of differentially rotating neutron stars
Paweł Szewczyk
Date: 17.01.2024
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Strongly differential rotation is expected in the neutron stars formed in collapse of a massive stellar core and in remnants of binary neutron star mergers. This allows for neutron stars with much more mass than possible without rotation. Although the rotation becomes rigid on a longer timescales, its differential nature may be crucial for dynamical stability of BNS mergers and CCSN remnants. There is no clear threshold of dynamical instability of these objects that would indicate how much mass can be stabilized in the early phase of their life.
We performed a series of numerical simulations to recognize the growth of various instabilities. We find the threshold to collapse against quasi-radial perturbations and inspect the non-axisymmetrical instabilities. I will present the results of these studies and discuss their importance in the context of future observations.
Historia krakowskiej fizyki teoretycznej w latach 1945-2015: Acta Cosmologica w latach 1973–1998 (Zeszyty Naukowe UJ redagowane przez pracowników Obserwatorium Astronomicznego UJ)
Zdzisław Golda
Date: 10.01.2024
Start Time: 12:00
Place: D-2-02
Organiser: ZTWiA
Contact: prof. dr hab. Edward Malec
Streszczenie wykładu:
Acta Cosmologica należące do serii Zeszytów Naukowych Uniwersytetu Jagiellońskiego, których pierwszy numer ukazał się w 1973 roku, otwarły lokalnemu środowisku naukowemu astronomów możliwość publikowania swoich prac również w Krakowie.
Tematyka przedstawiana w Zeszytach była szeroka: od katalogu galaktyk Pola Jagiellońskiego przez ich opracowanie statystyczne, tematykę radioastronomiczną do zagadnień kosmologicznych i wielu innych. Znalazły się tam również materiały z kilku Krakowskich Szkół Kosmologicznych i konferencji międzynarodowych. W Zeszytach są też opracowania bibliograficzne dotyczące pokrewnych, ciekawych zagadnień, notki biograficzne itp.
Autorami artykułów byli nie tylko pracownicy Obserwatorium Astronomicznego, ale również szereg innych badaczy nie związanych zawodowo z tą placówką.
Inne kwestie:
i) korespondencja z profesorem Andrzejem Kajetanem Wróblewskim o Katedrze Teoretycznej Fizyki Jądrowej;
ii) sprawy organizacyjne.
Maximal entropy random walk - could its stronger localization affect dust statistics?
Jarosław Duda
Date: 10.01.2024
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Hubble constant in the inhomogeneous model of the local universe
Szymon Sikora
Date: 20.12.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Quantum spacetime
Andrzej Góźdź
Date: 13.12.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Measures and measurements on spacetimes
Michał Eckstein
Date: 6.12.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
NUT spacetimes with U(1) symmetry
Maciej Ossowski
Date: 29.11.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Spacetimes with the NUT parameter, although closely related to Schwarzschild and Kerr solutions, are notoriously difficult to interpret. One of the reasons is the singularity of the axis of rotation, which in the non-rotating case is remedied by the periodic identification of time - co called Misner interpretation. I will show how to extend of this interpretation to the case of rotating, spherical black holes (accelerated Kerr-NUT-(anti-) de Sitter spacetimes), by imposing a suitable U(1) bundle structure. I will relate this approach to the local study of the black holes, i.e. Isolated Horizon (IH) with the Einstein Equations reduced to the so called Petrov Type D equation and provide a geometrical characterization of His embeddable in a generic accelerated Kerr-NUT-(anti-) de Sitter spacetime. Finally I will use this approach to breach the remaining gap in classification of smooth IH by deriving all Type D IHs admitting a non-trivial U(1) bundle structure over a compact Riemann surface with genus >0.
Infrared and Ultraviolet limits of CDT (making contact with asymptotic safety)
Jakub Gizbert-Studnicki
Date: 22.11.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Einstein-Weyl geometry and dispersionless Kadomtsev-Petviashvili equation
Jerzy Knopik
Date: 15.11.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Divergenceless fields in irrotational flow
Krzysztof Głód
Date: 11.10.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: dr hab. Patryk Mach
Monte Carlo simulations of general-relativistic accretion problems and the Bertrand paradox
Patryk Mach
Date: 14.06.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: prof. dr hab. Piotr Bizoń
Toy model for boson stars
Jerzy Knopik
Date: 31.05.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: prof. dr hab. Piotr Bizoń
I will review the possibility of existence of boson stars (Q-balls) which arise as solution to massive Einstein-Klein-Gordon theory. I will consider a toy model for boson stars which consists of a complex-valued Klein-Gordon equation with cubic and quintic terms on 3+1 Minkowski spacetime. I will discuss the spectral stability of the stationary states to the equation.
Weighing spacetime along the line of sight using times of arrival of electromagnetic signals
Mikołaj Korzyński
Date: 24.05.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: prof. dr hab. Piotr Bizoń
I will present a method of determining the mass density along the line of sight using variations of times of arrival of electromagnetic signals, as measured by two ensembles of free falling, precise clocks. The whole set-up may be considered a type of an extended gravitational compass, i.e. a device measuring directly the spacetime curvature using an ensemble of communicating clocks. I will also discuss the geometric interpretation of this measurement.
Wave dynamics on bounded domains
Maciej Maliborski
Date: 17.05.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: prof. dr hab. Piotr Bizoń
We study a toy-model Hamiltonian PDE defined on a bounded domain. In particular, we construct time-periodic solutions and study their properties.
Quantum Mechanics of Gravitational Waves
George Zahariade
Date: 10.05.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Contact: prof. dr hab. Piotr Bizoń
We study the effect of a quantized gravitational wave on a LIGO/VIRGO-type gravitational wave detector. We find that the arm-length is subject to a stochastic tidal force whose properties depend on the exact quantum state of the gravitational field, if the gravitational field is quantized. The quantum nature of gravity could thus (in principle) be detectable as an additional noise source at gravitational wave detectors.
Refs:
1) M. Parikh, F. Wilczek, and G. Zahariade, Phys. Rev. Lett. 127, 081602 (2021) - arxiv:2010.08205
2) M. Parikh, F. Wilczek, and G. Zahariade, Phys. Rev. D 104, 046021 (2021) - arxiv:2010.08208
Asymptotic stability of kinks in the odd energy space
Michał Kowalczyk
Date: 19.04.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
In this talk I will first present a 10 years old result about the asymptotic stability of the kink in the classical $\phi^4$ model under the assumption of oddness of the initial perturbations. I will explain how the problem can be decomposed into radiation and internal modes and how the components can be controlled through virial estimates. This result depends on some numerical approximations and its proof can be viewed as computer assisted. Recently, we were able to generalize the asymptotic stability result to one dimensional scalar field models with one internal mode. I will show how using the Darboux factorization of the linearized operator around the kink one can avoid numerical approximations.
Revisiting timelike and null geodesics in the Kerr spacetime: general expressions in terms of Weierstrass elliptic functions
Adam Cieślik
Date: 12.04.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
I will present the theory of Kerr geodesics. Based on a Weierstrass-Biermann theorem, I will derive two formulas, one for radial motion and one for altitude motion, both describing all non radial, timelike and null trajectories in terms of Weierstrass elliptic functions. These will be a generalisation of last year's method, which describes geodesics in the Schwarzschild metric. Two single expressions work remarkably for an entire geodesic trajectory, whether equatorial or not, even if it passes through turning points. With their help, I will show how to derive expressions for the azimuthal angle and coordinate time along the geodesic.
Elizabethan Vortices
Maciej Dunajski
Date: 5.04.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Abelian vortices are solitons in two space dimensions, with finite core size.
I will explain how radial solutions to the sinh–Gordon equation and the elliptic Tzitzeica equation can be interpreted as abelian vortices on certain surfaces of revolution. These surfaces have a conical excess angle at infinity (in a way which makes them similar to Elizabethan ruff collars, or certain green algae). They can not be embedded in the Euclidean 3-space but can be globally embedded in the hyperbolic space. I will show pictures of these embeddings, and discuss their existence which follows from the asymptotic analysis of a Painleve III ODE.
On Jeans instability, Bonnor’s correction and General Relativity
Edward Malec
Date: 29.03.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
There exists a very old argument of Jeans that led to a criterion on the formation of bound gaseous structures within the Newtonian hydrodynamics. The argument is obviously wrong and much later Bonnor presented a correct reasoning, that suprisingly produced almost the same (Jeans’s) criterion. This result of Bonnor is commonly known as being valid within the Newtonian cosmological universe, but we shall demonstrate that in fact the Bonnor model almost coincides with a general-relativistic Friedman-Lemaitre-Robertson-Walker cosmology. In particular, it yields the same (Jeans) criterion for the mass content of bound systems.
Chaos and Einstein-Rosen waves
Sebastian Szybka
Date: 22.03.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
We show existence of chaotic geodesics for the Einstein-Rosen standing gravitational waves. We present the fractal associated with the system studied. The complicated dynamics in this vacuum spacetime is governed by the chaotic heteroclinic network which makes it similar to the cognitive dynamics.
Dynamics of kink clusters for scalar fields in dimension 1+1
Jacek Jendrej
Date: 15.03.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
We consider classical scalar fields in dimension 1+1 with a self-interaction potential being a symmetric double-well. Such a model admits non-trivial static solutions called kinks and antikinks. A kink cluster is a solution approaching, for large positive times, a superposition of alternating kinks and antikinks whose velocities converge to 0 and mutual distances grow to infinity. Our main result is a determination of the asymptotic behaviour of any kink cluster at the leading order.
Our results are partially inspired by the notion of "parabolic motions" in the Newtonian n-body problem. I will present this analogy and mention its limitations. If time allows, I will explain the role of kink clusters as universal profiles for formation of multi-kink configurations.
This is a joint work with Andrew Lawrie from MIT.
Magnus effect for rotating black hole?
Andrzej Odrzywołek
Date: 8.03.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Asymptotically static equivariant wave maps on a wormhole
Piotr Bizoń
Date: 1.03.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Nauka w Ukrainie w czasie wojny
Volodymyr Pelykh
Date: 1.02.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Selected aspects of relativistic structure formation
Jan Ostrowski
Date: 25.01.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Medial Axis - the geodesic intersections points
Adam Białożyt
Date: 18.01.2023
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Distance reciprocity and symplectic evolution of observed ray bundles
Nezihe Uzun
Date: 14.12.2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Topological defects with electromagnetic + gravitomagnetic interactions
Jarosław Duda
Date: 30.11.2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Classical electromagnetism has two weaknesses: Gauss law allows for non-integer charges, and infinite energy of electric field of a charge. I will start with Faber's model repairing both: defining electric field as curvature of a deeper vector field Gauss law counts topological charge which is quantized, Higgs-like potential deforms the field to finite energy, also getting tiny Coulomb corrections in agreement with the running coupling effect. Then I will discuss its Landau-de Gennes-like extension to field of 3x3 matrices, among others adding low energetic O(1) degree of freedom resembling quantum phase, governed by Klein-Gordon-like dynamics. Finally extending to 4D tensor field adds dynamics governed by second set of Maxwell equations as in gravitoelectromagnetic approximation of the general relativity. Slides, materials: https://github.com/JarekDuda/liquid-crystals-particle-models
O interpretacji mechaniki kwantowej
Andrzej Staruszkiewicz
Date: 23.11.2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Pulsar timing in extreme mass ratio binaries
Eva Hackmann
Date: 16. 11. 2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Pulsar timing offers excellent capabilities to test the theory of gravity in the strong field regime. Particularly promising laboratories for such tests are pulsar – black hole binaries, and the search for pulsars closely orbiting the supermassive galactic center black hole is ongoing. Complementary to the post-Newtonian approach commonly employed in pulsar timing, here the test particle approximation provides another useful ansatz.
We present an analytical expression for the propagation time delay in a Kerr spacetime, including the post-Newtonian Shapiro and frame dragging delays as well as effects due to the multipole structure of the Kerr black hole. As an specific example we discuss in detail the most extreme case of an equatorial egde on pulsar orbit and compare our results to the usual post-Newtonian expressions.
Observational properties of bosonic stars from geodesic motion
Joao Rosa
Date: 26. 10. 2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
In the recent years, our understanding of the galactic centre has grown rapidly with the joint efforts of large international collaborations like the GRAVITY, who detected infrared flares close to the innermost stable circular orbit (ISCO) of the supermassive black-hole at the galactic centre, and the Event Horizon Telescope (EHT), which recently published the first picture of a black-hole shadow from Sgr A*. These observations are consistent with the predictions from General Relativity (GR) in black-hole spacetimes. However, due to the large experimental imprecisions, the data are not able to exclude the possibility of the central massive object in our galaxy not being a black-hole but instead some exotic compact object that mimics the qualitative properties of black-hole exteriors. In this talk, we explore a particular example of such alternative compact objects: bosonic stars (Boson and Proca stars), and the possibility of these observations being consistent with the presence of one of these exotic stars at the galactic centre.
Equatorial accretion on the Kerr black hole
Andrzej Odrzywołek
Date: 19. 10. 2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Gravitational dipole and quadrupole radiation from pulsars
Paritosh Verma
Date: 12. 10. 2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
Cepheid variables in the times of the Hubble constant tension.
Grzegorz Pietrzyński
Date: 18. 05. 2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
I will discuss the most important problems related to distance determination with classical Cepheids and our current capabilities of using these stars to calibrate SN Ia and as the result to determine the Hubble constant. I will also comment on the role of classical Cepheids in the process of studying one of the most important problem in the history of science - the Hubble tension.
Spectral Instability in Yang-Mills Solitons
Bradley Cownden
Date: 26. 04. 2022
Start Time: 10:15
Place: D-2-02
Organiser: ZTWiA
The quasinormal modes (QNMs) of a system, i.e. the exponentially damped, oscillatory solutions to linear wave equations, encode fundamental information about the system being studied. A familiar example is the spectroscopic analysis of QNMs of coalescing black hole binaries, which is used to obtain information about the mass and spin of the final state. The question of whether QNMs are stable or unstable under small perturbations is answered by the pseudospectrum. In this talk we discuss ongoing work into the examination of the pseudospectrum of the equivariant Yang-Mills soliton in (4+1)-dimensions. We discuss the hyperboloidal compactifications that allow us to determine the QNMs of the soliton not by the imposition of boundary conditions, but rather by appropriate regularity conditions on the solution. We then introduce the notion of the pseudospectrum and how it can be used to examine the stability of the QNMs under different types of perturbations. Finally, we contrast the spectral stability of solitons with what is already known about the spectral stability of Schwarzschild and Reissner-Nordstrom black holes.