003.05. Energetic Cosmos LaboratoryNo Descriptionhttps://nur.nu.edu.kz/handle/123456789/82182024-10-13T05:13:39Z2024-10-13T05:13:39Z181EXTREME ELECTRON ACCELERATION WITH FIXED RADIATION ENERGYGood, Michael R. R.Singha, ChiranjeebZarikas, Vasilioshttps://nur.nu.edu.kz/handle/123456789/70132024-08-22T03:55:09Z2022-01-01T00:00:00Zdc.title: EXTREME ELECTRON ACCELERATION WITH FIXED RADIATION ENERGY
dc.contributor.author: Good, Michael R. R.; Singha, Chiranjeeb; Zarikas, Vasilios
dc.description.abstract: We examine the extreme situation of radiation from an electron that is asymptotically accelerated to the speed of light, resulting in finite emission energy. The analytic solution explicitly demonstrates the difference between radiation power loss and kinetic power loss (null).
2022-01-01T00:00:00ZA NUMERICAL STUDY OF STELLAR DISCS IN GALACTIC NUCLEIPanamarev, TarasKocsis, Bencehttps://nur.nu.edu.kz/handle/123456789/70022024-08-22T03:55:26Z2022-01-01T00:00:00Zdc.title: A NUMERICAL STUDY OF STELLAR DISCS IN GALACTIC NUCLEI
dc.contributor.author: Panamarev, Taras; Kocsis, Bence
dc.description.abstract: We explore the dynamics of stellar discs in the close vicinity of a supermassive black hole (SMBH) by means of direct N-body simulations. We show that an isolated nuclear stellar disc exhibits anisotropic mass segregation meaning that massive stars settle to lower orbital inclinations and more circular orbits than the light stars. However, in systems in which the stellar disc is embedded in a much more massive isotropic stellar cluster, anisotropic mass segregation tends to be suppressed. In both cases, an initially thin stellar disc becomes thicker, especially in the inner parts due to the fluctuating anisotropy in the spherical component. We find that vector resonant relaxation is quenched in the disc by nodal precession, but it is still the most efficient relaxation process around SMBHs of mass 106M⊙
and above. Two-body relaxation may dominate for less massive SMBHs found in dwarf galaxies. Stellar discs embedded in massive isotropic stellar clusters ultimately tend to become isotropic on the local two-body relaxation time-scale. Our simulations show that the dynamics of young stars at the centre of the Milky Way is mostly driven by vector resonant relaxation leading to an anticorrelation between the scatter of orbital inclinations and distance from the SMBH. If the S-stars formed in a disc less than 10 Myr ago, they may coexist with a cusp of stellar mass black holes or an intermediate mass black hole with mass up to 1000M⊙
to reproduce the observed scatter of angular momenta.
2022-01-01T00:00:00ZNGC 6240 SUPERMASSIVE BLACK HOLE BINARY DYNAMICAL EVOLUTION BASED ON CHANDRA DATASobolenko, MKompaniiets, OBerczik, PMarchenko, VVasylenko, AFedorova, EShukirgaliyev, Bhttps://nur.nu.edu.kz/handle/123456789/70012024-08-22T03:55:42Z2022-01-01T00:00:00Zdc.title: NGC 6240 SUPERMASSIVE BLACK HOLE BINARY DYNAMICAL EVOLUTION BASED ON CHANDRA DATA
dc.contributor.author: Sobolenko, M; Kompaniiets, O; Berczik, P; Marchenko, V; Vasylenko, A; Fedorova, E; Shukirgaliyev, B
dc.description.abstract: The main idea of our research is to estimate the physical coalescence time of the double supermassive black hole (SMBH) system in the centre of NGC 6240 based on the X-ray observations from the Chandra space observatory. The spectra of the northern and southern nuclei were fitted by spectral models from Sherpa and both presented the narrow component of the Fe Kα emission line. It enabled us to apply the spectral model to these lines and to find relative offset ≈0.02 keV. The enclosed dynamical mass of the central region of NGC 6240 with radius 1 kpc was estimated ≈2.04×1011M⊙
. These data allowed us to carry on the high-resolution direct N-body simulations with Newtonian and post-Newtonian (up to 2.5PN
correction) dynamics for this particular double SMBH system. As a result, from our numerical models, we approximated the central SMBH binary merging time for the different binary eccentricities. In our numerical parameters range, the upper limit for the merging time, even for the very small eccentricities, is still below ≈70 Myr. Gravitational waveforms and amplitude-frequency pictures from such events can be detected using pulsar timing array projects at the last merging phase.
2022-01-01T00:00:00ZUNDERSTANDING THE ‘FEEBLE GIANT’ CRATER II WITH TIDALLY STRETCHED WAVE DARK MATTERPozo, AlvaroBroadhurst, TomEmami, RaziehSmoot, Georgehttps://nur.nu.edu.kz/handle/123456789/70002024-08-22T03:55:59Z2022-01-01T00:00:00Zdc.title: UNDERSTANDING THE ‘FEEBLE GIANT’ CRATER II WITH TIDALLY STRETCHED WAVE DARK MATTER
dc.contributor.author: Pozo, Alvaro; Broadhurst, Tom; Emami, Razieh; Smoot, George
dc.description.abstract: The unusually large ‘dwarf’ galaxy Crater II, with its small velocity dispersion, ≃3 km s−1, defies expectations that low-mass galaxies should be small and dense. We combine the latest stellar and velocity dispersion profiles finding Crater II has a prominent dark core of radius ≃0.71+0.09−0.08
kpc, surrounded by a low density halo, with a transition visible between the core and the halo. We show that this profile matches the distinctive core-halo profile predicted by ‘Wave Dark Matter’ as a Bose-Einstein condensate, ψDM, where the ground state soliton core is surrounded by a tenuous halo of interfering waves, with a marked density transition predicted between the core and halo. Similar core-halo structure is seen in most dwarf spheroidal galaxies (dSphs), but with smaller cores, ≃0.25 kpc and higher velocity dispersions, ≃9 km s−1, and we argue here that Crater II may have been a typical dSph that has lost most of its halo mass to tidal stripping, so its velocity dispersion is lower by a factor of 3 and the soliton is wider by a factor of 3, following the inverse scaling required by the Uncertainty Principle. This tidal solution for Crater II in the context of ψDM is supported by its small pericenter of ≃20 kpc established by Gaia, implying significant tidal stripping of Crater II by the Milky Way is expected.
2022-01-01T00:00:00ZDEEP LEARNING UNRESOLVED LENSED LIGHT CURVESDenissenya, MikhailLinder, Eric Vhttps://nur.nu.edu.kz/handle/123456789/69992024-08-22T03:56:14Z2022-01-01T00:00:00Zdc.title: DEEP LEARNING UNRESOLVED LENSED LIGHT CURVES
dc.contributor.author: Denissenya, Mikhail; Linder, Eric V
dc.description.abstract: Gravitationally lensed sources may have unresolved or blended multiple images, and for time varying sources, the light curves from individual images can overlap. We use convolutional neural nets to both classify the light curves as due to unlensed, double, or quad lensed sources and fit for the time delays. Focusing on lensed supernova systems with time delays Δt ≳ 6 d, we achieve 100 per cent precision and recall in identifying the number of images and then estimating the time delays to σΔt ≈ 1 d, with a 1000× speedup relative to our previous Monte Carlo technique. This also succeeds for flux noise levels ∼10 per cent
. For Δt ∈ [2, 6] d, we obtain 94–98 per cent accuracy, depending on image configuration. We also explore using partial light curves where observations only start near maximum light, without the rise time data, and quantify the success.
2022-01-01T00:00:00ZOUT OF ONE, MANY: DISTINGUISHING TIME DELAYS FROM LENSED SUPERNOVAEDenissenya, MikhailBag, SatadruKim, Alex GLinder, Eric VShafieloo, Armanhttps://nur.nu.edu.kz/handle/123456789/69982024-08-22T03:56:29Z2022-01-01T00:00:00Zdc.title: OUT OF ONE, MANY: DISTINGUISHING TIME DELAYS FROM LENSED SUPERNOVAE
dc.contributor.author: Denissenya, Mikhail; Bag, Satadru; Kim, Alex G; Linder, Eric V; Shafieloo, Arman
dc.description.abstract: Gravitationally lensed Type Ia supernovae are an emerging probe with great potential for constraining dark energy, spatial curvature, and the Hubble constant. The multiple images and their time delayed and magnified fluxes may be unresolved, however, blended into a single light curve. We demonstrate methods without a fixed source template matching for extracting the individual images, determining whether there are one (no lensing) or two or four (lensed) images, and measuring the time delays between them that are valuable cosmological probes. We find 100 per cent success for determining the number of images for time delays greater than ∼10 d.
2022-01-01T00:00:00ZCONSTRAINING SCALE DEPENDENT GROWTH WITH REDSHIFT SURVEYSDenissenya, MikhailLinder, Eric V.https://nur.nu.edu.kz/handle/123456789/69942024-08-22T03:56:43Z2022-01-01T00:00:00Zdc.title: CONSTRAINING SCALE DEPENDENT GROWTH WITH REDSHIFT SURVEYS
dc.contributor.author: Denissenya, Mikhail; Linder, Eric V.
dc.description.abstract: Ongoing and future redshift surveys have the capability to measure the growth rate of large scale structure at the percent level over a broad range of redshifts, tightly constraining cosmological parameters. Beyond general relativity, however, the growth rate in the linear density perturbation regime can be not only redshift dependent but scale dependent, revealing important clues to modified gravity. We demonstrate that a fully model independent approach of binning the gravitational strength Geff (k,z) matches scalar-tensor results for the growth rate fσ8(k,z) to 0.02%–0.27% rms accuracy. For data of the quality of the Dark Energy Spectroscopic Instrument (DESI) we find the bin values can be constrained to 1.4%–28%. We also explore the general scalar-tensor form, constraining the amplitude and past and future scalaron mass/shape parameters. Perhaps most interesting is the strong complementarity of low redshift peculiar velocity data with DESI-like redshift space distortion measurements, enabling improvements up to a factor 6–7 on 2D joint confidence contour areas. Finally, we quantify some issues with gravity parametrizations that do not include all the key physics.
2022-01-01T00:00:00ZDOUBLE SOURCE LENSING PROBING HIGH REDSHIFT COSMOLOGYSharma, DivijLinder, Eric V.https://nur.nu.edu.kz/handle/123456789/69932024-08-22T03:56:59Z2022-01-01T00:00:00Zdc.title: DOUBLE SOURCE LENSING PROBING HIGH REDSHIFT COSMOLOGY
dc.contributor.author: Sharma, Divij; Linder, Eric V.
dc.description.abstract: Double source lensing, with two sources lensed by the same foreground galaxy,
involves the distance between each source and the lens and hence is a probe of the universe
away from the observer. The double source distance ratio also reduces sensitivity to the lens
model and has good complementarity with standard distance probes. We show that using
this technique at high redshifts z > 1, to be enabled by data from the Euclid satellite and
other surveys, can give insights on dark energy, both in terms of w0–wa and redshift binned
density. We find a dark energy figure of merit of 245 from combination of 256 double source
systems with moderate quality cosmic microwave background and supernova data. Using
instead five redshift bins between z = 1.1–5, we could detect the dark energy density out to
z ≈ 5, or make measurements ranging between 31σ and 2.5σ of its values in the bins.
2022-01-01T00:00:00ZON THE DUALITY OF SCHWARZSCHILD-DE SITTER SPACETIME AND MOVING MIRRORFernandez-Silvestre, DiegoFoo, JoshuaGood, Michael R.R.https://nur.nu.edu.kz/handle/123456789/65142024-08-22T03:57:13Z2022-01-01T00:00:00Zdc.title: ON THE DUALITY OF SCHWARZSCHILD-DE SITTER SPACETIME AND MOVING MIRROR
dc.contributor.author: Fernandez-Silvestre, Diego; Foo, Joshua; Good, Michael R.R.
dc.description.abstract: The Schwarzschild-de Sitter (SdS) metric is the simplest spacetime solution in general relativity with both a
black hole event horizon and a cosmological event horizon. Since the Schwarzschild metric is the most simple
solution of Einstein’s equations with spherical symmetry and the de Sitter metric is the most simple solution
of Einstein’s equations with a positive cosmological constant, the combination in the SdS metric defines an
appropriate background geometry for semi-classical investigation of Hawking radiation with respect to past and
future horizons. Generally, the black hole temperature is larger than that of the cosmological horizon, so there is
heat flow from the smaller black hole horizon to the larger cosmological horizon, despite questions concerning
the definition of the relative temperature of the black hole without a measurement by an observer sitting in
an asymptotically flat spacetime. Here we investigate the accelerating boundary correspondence (ABC) of the
radiation in SdS spacetime without such a problem. We have solved for the boundary dynamics, energy flux
and asymptotic particle spectrum. The distribution of particles is globally non-thermal while asymptotically the
radiation reaches equilibrium
2022-01-01T00:00:00ZBLACK HOLE HOOKEAN LAW AND THERMODYNAMIC FRAGMENTATION: INSIGHTS FROM THE MAXIMUM FORCE CONJECTURE AND RUPPEINER GEOMETRYGennaro, Sofia DiGood, Michael R. R.Ong, Yen Chinhttps://nur.nu.edu.kz/handle/123456789/64702024-08-22T03:57:37Z2022-01-01T00:00:00Zdc.title: BLACK HOLE HOOKEAN LAW AND THERMODYNAMIC FRAGMENTATION: INSIGHTS FROM THE MAXIMUM FORCE CONJECTURE AND RUPPEINER GEOMETRY
dc.contributor.author: Gennaro, Sofia Di; Good, Michael R. R.; Ong, Yen Chin
dc.description.abstract: We show that the notion of “Hookean law” F = kx, suitably defined in asymptotically flat singly spinning
Myers-Perry black hole space-times in dimensions d 5, is related to the Emparan-Myers fragmentation
(splitting of a black hole into two becomes thermodynamically preferable). Specifically, the values of black hole
parameters when fragmentation occurs correspond to the maximal value of F. Furthermore this always happens
before F reaches 1/4 in Planck units. These results suggest that a version of “maximum force conjecture” may be
relevant for black hole thermodynamics. We also relate these findings to the Ruppeiner thermodynamic geometry
of these black holes and speculate on the implications for the underlying microstructures of black hole horizons.
2022-01-01T00:00:00Z