Astrophysics of Galaxies · Cross-listed from hep-ph
Constraining dark matter self-interaction from kinetic heating in neutron stars
Sambo Sarkar
Dark matter search strategies have started advancing towards the
neutrino fog. In this regard, compact objects such as
neutron stars have already demonstrated their ability in probing such low DM-nucleon cross-sections from dark matter induced effects. In the optically thin limit, effect of dark matter self-interaction becomes relevant and may assist the capture and thermalization of dark matter inside
stars, imparting observable changes on
neutron star temperatures. The resulting radiation although weak can be potentially detected by the James Webb Space
Telescope and upcoming Thirty Meter
Telescope and the European Extremely Large
Telescope. Observation of cold
neutron stars accompanied by advancements in direct detection probes would provide stringent constraints or a smoking-gun signature for dark matter self-interactions. The potential detection of a
neutron star with surface temperatures $\sim (1000 - 1200)$ K in the optically thin limit can push the bounds on asymmetric dark matter self-interaction cross-section to approximately two orders of magnitude more stringent than the bullet cluster.
Read the full abstract ▾
Solar and Stellar Astrophysics
Modeling of the magnetic stellar wind braking of the ssrAp 33 Lib (HD137949)
A.G. Nikiforov, V.D. Bychkov and M.V. Barkov
Using the ssrAp
star 33 Lib (HD137949) as an example, we show that
magnetic braking caused by the interaction of a strong
magnetic field with a
stellar wind can play a key role in slowing the rotation of ssrAp
stars. Numerical modeling of
stellar rotation
spin-down in the MESA package, taking into account the
evolution of
magnetic fields and the
stellar wind, shows that
stars with rotation periods of up to 80 years and longer can form. Moreover, braking by a magnetized wind makes it possible to estimate the mass-loss rate for
stars of moderate mass ($1.25 M_\odot < M < 2 M_\odot$), which is difficult to do by other methods. We introduce the dimensionless parameter $\Xi$, which reflects the
spin-down time and the
stellar lifetime. Thus, when $\Xi \gg 1$, braking is important, whereas when $\Xi \ll 1$, it is negligible.
Read the full abstract ▾
Astrophysics of Galaxies
An Old, Low-mass, Metal-poor Hypervelocity Star Candidate Consistent with a Galactic Center Origin
Shunhong Deng, Yang Huang, Haozhu Fu et al. (+4 more)
We report the discovery of DESI-HVS1, a hypervelocity
star (HVS) candidate identified from DESI DR1 spectroscopy and
Gaia DR3 astrometry. DESI-HVS1 is an old, low-mass, metal-poor F-type
star with a mass of $0.8\,M_\odot$, an age of $\sim14.1$~Gyr, and $\mathrm{[Fe/H]}=-1.6$. It is located at a heliocentric distance of $3.77^{+0.39}_{-0.36}$~kpc and has a Galactocentric total velocity of $523^{+46}_{-47}\,\mathrm{km\,s^{-1}}$, marginally exceeding the local escape speed, corresponding to an unbound probability of $P_{\rm ub} \sim 50\%$. Backward orbit integrations show that DESI-HVS1 had a closest approach to the
Galactic center (GC) of $0.40^{+0.23}_{-0.11}\,\mathrm{kpc}$, with a velocity of $682^{+22}_{-35}\,\mathrm{km\,s^{-1}}$ and a flight time of $12.89^{+0.92}_{-0.74}\,\mathrm{Myr}$. The reconstructed orbit exhibits a clear perigalactic turning point and only a single crossing of the
Galactic midplane ($P_{\rm cross} > 0.95$). These properties suggest that DESI-HVS1 is most naturally explained by the Hills mechanism, although alternative scenarios cannot be entirely ruled out. Its discovery provides the first strong evidence for an old, low-mass HVS candidate consistent with a GC origin, indicating that the apparent dominance of young, massive GC-origin HVSs is likely a consequence of observational selection effects.
Read the full abstract ▾
All authors Shunhong Deng, Yang Huang, Haozhu Fu, Yongkang Sun, Qikang Feng, Guoyang Chen, Huawei Zhang
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Exploring the statistical anisotropy of primordial curvature perturbations with pulsar timing arrays
Fengting Xie, Zhi-Chao Zhao, Qing-Hua Zhu et al. (+1 more)
The recent detection of a
stochastic gravitational wave background by
pulsar timing arrays has opened a new window in understanding supermassive black hole binaries and in probing the universe at the early time. Recently,
pulsar timing array (PTA) collaborations have been further paving the way to probe anisotropies in the
stochastic gravitational wave background. This study investigates dipole-type statistical anisotropy in the
primordial power spectrum within a phenomenological framework. We demonstrate that the
primordial dipole induces both dipolar and quadrupolar anisotropies in the energy density spectrum of scalar-induced gravitational waves (SIGWs), without generating extra polarization modes. Based on this anisotropic spectrum, we derive the corresponding PTA overlap reduction functions (ORFs), which exhibit frequency dependence, with the anisotropies enhanced on small scales. Furthermore, owing to the non-uniform distribution of millisecond
pulsars over the sky in current PTA
dataset, the ORFs exhibit a morphology that explicitly depends on the preferred direction of the anisotropy. However, our
bayesian analysis of the NANOGrav 15-year
dataset still yields no significant evidence for a preferred direction and a weak upper limit on anisotropy amplitude $(g\lesssim0.5)$. This result arises because the observational frequency band lies below the spectral peak, where our models predict suppressed anisotropic contributions. This limitation highlights the potential of future PTA observations. Specifically,
datasets with broader frequency coverage are expected to tighten constraints on dipole-type anisotropy.
Read the full abstract ▾
All authors Fengting Xie, Zhi-Chao Zhao, Qing-Hua Zhu, Xin Li
Solar and Stellar Astrophysics
Tracking Magnetic Topological Change in a Time-Dependent Coronal Model
Emily I. Mason, Cooper Downs, Roberto Lionello et al. (+2 more)
We apply the slip-back mapping method of Titov et al. 2009 and Lionello et al. 2020 to a thermodynamic MHD simulation to track topological changes in the
magnetic field at a range of temporal cadences. The method constitutes the logical successor to a simple open-field map for a steady-state model, as it tracks changes in the open and closed fields for a time-dependent model by tracking individual
magnetic elements as they advect across the map, rather than simply tracing field line connectivity from each
cell. Through careful categorization of the slip-back mapping values and analysis of the flux changes, we not only effectively track the open flux but can recover the flux processed through interchange reconnection as well. The field lines involved in these processes are shown to follow lines of high squashing factor, as proposed by interchange reconnection-driven slow
solar wind theory. The time-dependent model, which is scaled to
solar minimum-like activity, projects that a median value of 3.5% of the total open flux in any given 24-hour interval has been processed through interchange reconnection. This corresponds to a relatively high proportion of the total open flux changes over time in the heliosphere. Our results show that not only is this method a useful tool for accurately tracking topological change in time-dependent simulations, but that its inherent complexity can be visually reduced into an intuitive 2D plot that simply and effectively communicates temporal changes.
Read the full abstract ▾
All authors Emily I. Mason, Cooper Downs, Roberto Lionello, Jon A. Linker, Viacheslav Titov
Cosmology and Nongalactic Astrophysics
Aspects of gravitational clustering and structure formation in the Universe
Swati Gavas
The distribution of
galaxies,
halo abundance, and peculiar velocities are influenced by non-linear gravitational interactions, making the study of non-linear
evolution crucial for accurate cosmological predictions. We explore these aspects using N-body simulations. Theoretical models of the
halo mass function (HMF) can be formulated without referencing a cosmological model or input power spectrum. HMF obtained from N-body simulations show systematic deviations of 5-20% from theoretical predictions. The physical origin of deviations may result from cosmology, the power spectrum, or both. We examine HMF deviations from universality for scale-free power spectra with an Einstein-de Sitter cosmology. We demonstrate that the mass function exhibits an explicit dependence on the slope of the input power spectrum. We find that an effective index of the $\Lambda$CDM model can correspond to the HMF from scale-free cosmologies as a first approximation. Furthermore, structure formation has led to deviations from homogeneity and isotropy on scales up to at least $100$ Mpc/h, expected to affect measurements of $H_0$. We revisit this issue of the concordance model. We find a correlation between errors in $H_0$ estimates and the density around the observer. Further, our mock observations reveal that deviations of up to 5% can occur in Milky Way-sized
halos. While this finding alone does not fully resolve the Hubble tension, it may account for part of it. It is essential to understand the limitations of N-body simulations to avoid misinterpreting data. We show that the missing power at small scales introduces errors in the root-mean-square fluctuations and in the simulated mass function. Our analytical calculation indicates that mode coupling between small and large scales depends on resolving collapsed
halos. Therefore, accurate mode coupling estimates require sufficient
halos in the simulation.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Multi-wavelength study of EP250416a / GRB 250416C: An Optically Dark Long GRB with a Late Jet Break
Guoying Zhao, Duo-Le Cao, Rong-Feng Shen et al. (+29 more)
We present multi-wavelength study of the $\gamma$/X-ray transient EP250416a (also designated GRB 250416C), triggered by the Einstein Probe (EP) Wide-field X-ray
Telescope and also by SVOM and Konus-Wind (KW). Observations spanning the $\gamma$-ray, X-ray, and optical bands facilitated detailed analysis of the burst's
prompt emission, afterglow
evolution, and physical origin. GRB 250416C exhibits a burst duration of 30 s in X-ray and 17.7 s in $\gamma$-rays, with joint spectral fitting of 0.5-5000 keV data gives $E\rm_{peak}=342_{-232}^{+90}$ keV. Optical spectroscopy of the afterglow, acquired with the Gemini Multi-Object Spectrograph (GMOS) on Gemini South, yielded a
redshift of $z=0.963$. Accounting for the measured
redshift, the isotropic energies are $E\rm_{X,iso}=2.7_{-0.5}^{+0.9}\times10^{50}$ erg and $E\rm_{\gamma,iso}=7.34_{-2.1}^{+5.1}\times10^{51}$ erg, aligning with the Amati relation for long GRBs. The fluence ratio $\rm S(25-50~keV)/S(50-100~keV)=0.78_{-0.12}^{+0.10}$ classifies GRB 250416C as an X-ray rich (XRR) GRB. The X-ray afterglow shows an initial shallow decay ($\alpha \approx -0.5$) transitioning to a canonical decay phase ($\alpha \approx -1$), with a very late jet break at $t\sim 1.5\times 10^6$ s, corresponding to a jet half-opening angle of $\theta _j=10.6_{-1.8}^{+1.9}$ degrees. GRB 250416C is optically dark, as it shows only a faint $r$-band detection ($r=24.16\pm 0.13$ mag) from Gemini South-GMOS and a low optical-to-X-ray spectral index $\beta_{\rm OX} = 0.3$. This may be attributed to significant host-
galaxy extinction, with a required $A_V^{\text{host}}=2.7\pm 0.3\ \text{mag}$ derived from the extinction curve model.
Read the full abstract ▾
All authors Guoying Zhao, Duo-Le Cao, Rong-Feng Shen, Hui Sun, Chi-Chuan Jin, Wei-Min Yuan, Chen-Wei Wang, Shao-Lin Xiong, Dmitry Svinkin, Dong Xu, Shuai-Qing Jiang, Peter G. Jonker, Yun Wang, Hao Zhou, Chang Zhou, Xinlei Chen, Kaushik Chatterjee, Xue-Feng Wu, Xiao-Feng Wang, Chun Chen, Yuan Liu, Andrew J. Levan, Jennifer Alexandra Chacon Chavez, Jonathan Quirola-Vásquez, Franz E. Bauer, Antonio Martin-Carrillo, Gregory Corcoran, Daniele B. Malesani, Dmitry Frederiks, Anna Ridnaia, Alexandra L. Lysenko, Mikhail Ulanov
Solar and Stellar Astrophysics
VLTI-GRAVITY measurements of cool evolved stars: II. Pulsation properties and mass-loss process of the Mira star R Car and the red supergiant VX Sgr
D. Jadlovský, M. Wittkowski, A. Chiavassa et al. (+9 more)
The mass-loss process of red supergiant (RSG) and asymptotic
giant branch (AGB)
stars and its relation to variability are poorly constrained. We study two evolved
stars, the Mira-type AGB
star R Car and the extreme RSG VX Sgr. Our sample comprises 54 VLTI-
GRAVITY snapshots taken over 7 years, being the largest VLTI time-series
dataset to date. We determine the angular diameter as a function of time. The radii of the photosphere ($R_{\star}$) and atomic atmospheric layers are variable and relate to the light curve with phase shifts, showing a maximum radius near visual brightness minima. The more extended CO layers show longer, irregular periods and maximum extensions of $\sim 1.3-1.7 \: R_{\star}$ for R Car, and of $\sim 1.5-2.2 \: R_{\star}$ for VX Sgr. Comparison with CO5BOLD simulations revealed a similar behavior. Furthermore, during 2020-2021, VX Sgr exhibited an extreme mass-loss event similar to that of Betelgeuse, preceded by two strong shocks and culminating with the extreme expansion of H$_2$O and CO layers, both up to $\sim 2.2 \: R_{\star}$. During this event, we detected Brackett $\gamma$ and Balmer emission lines, both of which are signatures of a shock propagating through the atmosphere. The Mira R Car showed a photospheric radius $R_{\star} = 280 \pm 25 \: \rm R_\odot$, with a fundamental mode (FM) pulsation amplitude $\sim13 \%$ of $R_{\star} $. During its active cycle, the RSG VX Sgr showed $R_{\star} = 1556 \pm 110 \: \rm R_\odot$ with FM amplitude $ \sim13 \%$ of $R_{\star} $, the same as R Car. During its quiescent cycle, it showed $R_{\star}= 1456 \pm 108 \: \rm R_\odot$ and low-amplitude pulsations near the first overtone, only $\sim4 \%$ of $R_{\star} $. This supports a steady mass loss for Miras related to stable, large-amplitude FM pulsation, whereas the mass-loss process for RSGs may be dominated by extreme events connected to changes in the pulsation mode.
Read the full abstract ▾
All authors D. Jadlovský, M. Wittkowski, A. Chiavassa, K. Kravchenko, B. Freytag, S. Höfner, J. Krtička, C. Paladini, G. Rau, M. Brož, T. Granzer, M. Weber
Instrumentation and Methods for Astrophysics
Diffraction in the ASPIICS coronagraph: observations and modeling
S. Shestov, A. N. Zhukov, R. Rougeot et al. (+11 more)
Context: ASPIICS is a
giant-baseline visible light
solar coronagraph, which relies on the millimetric positioning performance of the precision formation flying Proba-3 mission of the European Space Agency. Proba-3 was launched on 5 Dec 2024, and since then ASPIICS observes the
solar corona with the field of view (1.1-3) R_sun. Aims: Diffraction, in particular diffraction of
solar disk light on the external occulter, is known to provide a major source of straylight in coronagraphs. We aim to analyze diffracted light visible in ASPIICS images, compare it with the analytical-numerical diffraction model reported earlier, and fine-tune the model. Methods: We compare diffraction effects visible in ASPIICS data with simulated diffraction images; in particular, we compare the geometrical properties and the radiometric signal. The properties of the diffraction described in previous works suggest how to fine-tune the model in order to achieve a better correspondence with the observations. Results: Early ASPIICS observations, where diffraction is pronounced, fully confirm all the qualitative properties of diffracted light suggested by the model. After fine-tuning of the model we see quantitative correspondence of the level of 30% – 50%, depending on the configuration. Conclusions: The performed analysis allows (a) to validate our analytical-numerical model and justify the assumptions, and (b) to estimate the contribution of the diffracted light in the ASPIICS images. In the majority of the field of view the diffracted light is two orders of magnitude below the coronal signal.
Read the full abstract ▾
All authors S. Shestov, A. N. Zhukov, R. Rougeot, C. Aime, B. Bourgoignie, L. Dolla, N. Britavskiy, S. Fineschi, S. Gunar, P. Lamy, M. Mierla, H. Peter, P. Rudawy, K. Tsinganos
High Energy Astrophysical Phenomena
XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 – Orbital and Short-Term Variability of Iron Absorption
Kaito Ninoyu, Shinya Yamada, Natalie Hell et al. (+19 more)
We present the first high-resolution spectroscopy of the black hole high-mass X-ray binary Cygnus X-1 with XRISM, including orbital-phase-resolved analyses and tentative evidence of short-term variability in the Fe-K band on second timescales. Using data from the Performance Verification phase in April 2024, we analyzed spectral variability across orbital phases with the Resolve microcalorimeter and the Xtend CCD imager. The unprecedented resolution of Resolve reveals variability in highly ionized Fe absorption lines. The absorption features show orbital-phase-dependent variability in column density, ionization state, and blueshifted velocity, suggesting structural variations in the focused
stellar wind along the line of sight. We also find indications of subtle broadening of the neutral Fe emission profile. In addition, intensity-sorted spectroscopy during dip phases suggests possible variability on timescales of a few seconds in the absorption features, consistent with cooler, denser and lower-ionized gas clumps. Although the statistical significance is limited, these results hint that the
stellar wind and the X-rays from the
accretion disk around the black hole may interact on timescales as short as a few seconds. These XRISM results constrain wind-fed
accretion in Cyg X-1 and highlight Resolve's capability to probe
plasma environments in high-mass X-ray binaries.
Read the full abstract ▾
All authors Kaito Ninoyu, Shinya Yamada, Natalie Hell, Elisa Costantini, Oluwashina Adegoke, Paul Draghis, Ken Ebisawa, Javier A. Garcia, Edmund Hodges-Kluck, Shunji Kitamoto, Shogo Kobayashi, Takayoshi Kohmura, Aya Kubota, Jon M. Miller, Misaki Mizumoto, Tsunefumi Mizuno, Hiromitsu Takahashi, Yuusuke Uchida, Kazutaka Yamaoka, Sixuan Zhang, Ryota Tomaru, Seoru Ito
Cosmology and Nongalactic Astrophysics
Cosmological discrete self-similarity in primordial black hole formation
Luis E. Padilla, Tomohiro Harada, Ethan Milligan et al. (+1 more)
We demonstrate that discrete self-similarity (DSS), originally discovered in the collapse of a massless scalar field in an asymptotically flat system, survives in
primordial black hole (PBH) formation within an expanding cosmological background. Using fully relativistic numerical simulations of massless scalar-field collapse in an Friedmann-Lemaître-Robertson-Walker universe, we resolve the critical regime down to $|p-p_c|\sim 10^{-8}$, where $p$ and $p_c$ respectively are a parameter of the family of initial data and its threshold value, and find clear log-periodic oscillations in the PBH mass scaling relation. The detailed structure of these oscillations differs from that previously reported in the asymptotically flat case, exhibiting a more pronounced asymmetry between peaks and troughs. Analyzing two distinct families of initial data (Gaussian and piecewise rational
curvature profiles), we find critical exponents and DSS periods that differ slightly but are broadly consistent within uncertainties. The presence of DSS implies characteristic log-periodic modulations in the PBH mass spectrum, with potential consequences for PBH abundances and the spectrum of induced gravitational waves.
Read the full abstract ▾
All authors Luis E. Padilla, Tomohiro Harada, Ethan Milligan, David Mulryne
Astrophysics of Galaxies
SPURS: Bursty Star Formation in an Extremely Luminous Weak Emission Line Galaxy at $z=9.3$
Zuyi Chen, Daniel P. Stark, Charlotte A. Mason et al. (+8 more)
JWST has revealed a population of super-luminous early
galaxies with a volume density in excess of most expectations. The spectra reveal diverse properties: while some reveal strong emission lines characteristic of
galaxies in the midst of strong bursts, others show weak emission lines that could reflect old
stellar populations, large escape fractions, or post-burst
star formation histories. Through the JWST Cycle 4 large program SPURS, we have obtained ultra-deep (29 hr) rest-frame UV spectroscopy of a z=9.3 super-luminous ($M_{\rm UV}=-21.66$)
galaxy with large assembled
stellar mass (1.6$\times$10$^9$ $M_\odot$) and extremely weak emission lines (H$\beta$ EW $\approx25$~Å). The strong
stellar wind features and rest-optical line ratios suggest the
galaxy is already significantly enriched, with a
metallicity of 0.4–0.7~Z$_\odot$. The interstellar absorption lines reveal
outflows ($v\simeq -161$~km~s$^{-1}$) with a large neutral gas covering fraction, suggesting that the weak emission lines are not due to large escape fractions. The combination of the Balmer break, weak emission lines, and
stellar wind features constrains the
star formation history, indicating a recent burst of
star formation lasting 10–20 Myr followed by a downturn over the last 10~Myr. The observations suggest that $z\gtrsim 9$ weak emission line
galaxies such as this source can be explained by
stochastic star formation, provided that the downturns in
star formation are recent (i.e., <10 Myr prior to observation). The ultra-deep grating spectrum enables the IGM damping wing to be characterized, decoupling the effects of local absorption. The smooth Ly$\alpha$ break indicates that this source, one of the most massive
galaxies known at z>9, is likely situated in a small ionized bubble ($0.29_{-0.09}^{+0.11}$~pMpc), as is common at large neutral hydrogen fractions ($\bar{x}_{\rm HI}=0.81_{-0.21}^{+0.14}$).
Read the full abstract ▾
All authors Zuyi Chen, Daniel P. Stark, Charlotte A. Mason, Adele Plat, Viola Gelli, Peter Senchyna, Keerthi Vasan G. C., Ryan Endsley, Mengtao Tang, Michael W. Topping, Lily Whitler
High Energy Astrophysical Phenomena
XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 – highly ionized Iron absorption structures
Shinya Yamada, Natalie Hell, Elisa Costantini et al. (+18 more)
We present the first high-resolution X-ray spectral analysis of Cygnus X-1 using XRISM. The observation was carried out from April 7 to 10, 2024, covering the orbital phase range 0.65–0.17 during its low/hard state. Taking advantage of the exceptional energy resolution of the Resolve instrument, we examined highly ionized iron absorption lines and characterized the ionization states, column densities, and line-of-sight velocities of the absorbing
plasma. Spectral analysis revealed an ionization parameter of approximately 3, column densities of a few times 10^21 cm^-2, and a blueshifted velocity of approximately 100 km s^-1. The observation was divided into two phases: before and after orbital phase phi_orb = 0.9, corresponding to non-dipping and dipping intervals. While only weak absorption features were present before phi_orb = 0.9, strong absorption by He-like and H-like Fe appeared during the dipping phase. We measured equivalent widths of 2.3 eV, 0.4 eV, and 1.2 eV for He-like Fe K-alpha, and H-like Ly-alpha1 and Ly-alpha2, respectively, demonstrating the capability of XRISM Resolve to securely detect narrow absorption features of only a few eV. These measurements trace the motion of the absorbing material and offer insight into the kinematics and spatial distribution of the wind in the vicinity of the black hole. These findings enhance our understanding of wind-fed
accretion in Cygnus X-1 and highlight the importance of continued high-resolution X-ray observations to further constrain the physical properties of winds and
accretion flows in high-mass X-ray binaries.
Read the full abstract ▾
All authors Shinya Yamada, Natalie Hell, Elisa Costantini, Oluwashina Adegoke, McKinley Brumback, Paul Draghis, Ken Ebisawa, Javier A. Garcia, Edmund Hodges-Kluck, Shunji Kitamoto, Shogo Kobayashi, Takayoshi Kohmura, Aya Kubota, Jon M. Miller, Misaki Mizumoto, Tsunefumi Mizuno, Kaito Ninoyu, Hiromitsu Takahashi, Yuusuke Uchida, Kazutaka Yamaoka, Sixuan Zhang
Astrophysics of Galaxies
Signatures of Very Massive Stars in the Epoch of Reionization
Rui Marques-Chaves, Fabrice Martins, Daniel Schaerer et al. (+2 more)
We present ultra-deep ($\simeq 20-30$ hours), rest-frame UV spectroscopy with NIRSpec/JWST of two UV-bright
galaxies at $z\sim 8.7$, CEERS-1019 and CEERS-1025 ($Z_{\rm neb} \simeq 0.1 Z_{\odot}$), obtained as part of the JWST Cycle 4 SPURS large program. The spectra reveal exceptionally strong P-Cygni profiles in wind lines (NV $\lambda$1240 and CIV $\lambda$1550) and significant broad and strong HeII $\lambda$1640 emission ($\rm EW\simeq 2-4$ A). We compare the observations with synthetic
stellar population models at $Z_{\star} \simeq 0.1 Z_{\odot}$, both including and excluding very massive
stars (VMS). Models including VMS provide a markedly improved fit to the data relative to non-VMS models ($\Delta$AIC and $\Delta$BIC $> 70$), which fail to reproduce the observed strengths of the wind features. A comparison with empirical spectra of VMS-dominated systems in the local Universe further supports this interpretation. The best-fit VMS models imply extremely young ages of the
stellar populations ($\simeq 1.5-2.0$Myr) and high ionizing
photon production efficiencies ($\log \xi_{\rm ion} [\rm Hz erg^{-1}] \gtrsim 25.8$), exceeding those inferred from non-VMS models by $\sim 0.1-0.2$ dex. These results provide evidence for an overabundance of VMS at high-$z$ with an IMF extending well beyond $100 M_{\odot}$, and highlight their potential role in shaping the rest-frame UV spectra, chemical enrichment, and ionizing output of
galaxies in the early Universe.
Read the full abstract ▾
All authors Rui Marques-Chaves, Fabrice Martins, Daniel Schaerer, Miroslava Dessauges-Zavadsky, Ana Palacios
Cosmology and Nongalactic Astrophysics
Impact of the Infrared Cutoff on Structure Formation in Tsallis Holographic Dark Energy
Biswajit Das
We investigate the viability of Tsallis
holographic dark energy (THDE) models, focusing on the role of the infrared (IR) cutoff in the growth of
cosmic structures. Considering two commonly used choices of the cutoff, the particle horizon and the future event horizon, we analyze the
evolution of linear matter perturbations and compute the growth factor, growth rate, and the observable $f\sigma_8(z)$. These predictions are compared with observational data from
redshift-space distortion measurements. We find that the growth history is highly sensitive to the choice of IR cutoff. Models based on the future event horizon are consistent with observational data and can provide a fit comparable to, or slightly better than, the $\Lambda$CDM model for suitable values of the Tsallis parameter $\delta$. In contrast, models constructed using the particle horizon generally fail to reproduce the observed growth of structure. These results demonstrate that the viability of THDE models depends crucially on the choice of IR cutoff and highlight the importance of structure formation as a stringent test of generalized
holographic dark energy scenarios.
Read the full abstract ▾
Solar and Stellar Astrophysics
One's loss is (not) another's gain: Isotropic re-emission destabilizes mass transfer from radiative donor stars
K. D. Temmink, S. Justham and O. R. Pols
Non-conservative mass transfer plays a central role in close-binary
evolution, yet its effects on mass-transfer stability are uncertain. One widely adopted prescription, isotropic re-emission, is often assumed to promote stability compared to conservative mass transfer. We investigate the impact of isotropic re-emission on the stability of mass transfer in binaries with radiative envelopes that undergo delayed dynamical instability (DDI). We assess whether simplified criteria used in binary population synthesis codes accurately capture stability boundaries under varying mass-transfer efficiencies. We perform detailed
stellar evolution calculations for a set of representative binaries undergoing DDI. Varying the mass-transfer efficiency beta, we track the onset of instability and quantify the corresponding critical mass ratio. We compare our results with predictions from the commonly used
zeta-method, which is based on mass-radius exponents. We find that a lower mass-transfer efficiency destabilizes mass transfer in DDI systems, whereas the
zeta-method predicts that isotropic re-emission should stabilize it. The discrepancy arises because the
zeta-method fails to capture the full
evolution of the orbit and mass ratio during pre-instability mass transfer. In some cases, the critical mass ratio is underestimated by nearly a factor of two. Our findings show that isotropic re-emission can reduce, rather than enhance, DDI stability, underscoring the limitations of using fixed critical mass ratios and
zeta-based criteria. This highlights the need for calibrated prescriptions that capture the time-dependent
evolution of mass ratio and orbital separation, with direct implications for modelling X-ray binaries, symbiotic
stars, and double white
dwarfs, including their transient rates and delay-time distributions.
Read the full abstract ▾
Solar and Stellar Astrophysics
X-Shooting ULLYSES: Massive stars at low metallicity XV. On the metallicity dependence of B-supergiant mass-loss rates
O. Verhamme, J.O. Sundqvist, A. de Koter et al. (+21 more)
Context. For
stellar evolution models we rely on mass-loss rate prescriptions that show features that lack empirical confirmation, such as the bi-stability jump. This jump is an increase in mass loss in the decreasing temperature regime Teff 28-21 kK. Although papers compared empirical results to prescriptions,a large observational sample of B
stars for which the wind has been scrutinised over different
metallicities is still lacking. Aims. By modelling of both ultraviolet (ULLYSES) and optical (XShootU) spectra, we determined the
stellar and wind parameters, of 24 SMC B
stars ranging in Teff from 13 to 29 kK. By combining this sample with LMC studies, we compared the wind behaviour of B
stars in two different
metallicity regimes. We compared our results to common mass-loss rate prescriptions to test features present in these models and their
metallicity dependence. Methods. We have used the model atmosphere code fastwind and the genetic
algorithm code Kiwi-GA to fit the UV and optical spectra simultaneously. This allows us to determine wind properties including clumping behaviour. Results. The
metallicity trends present in the mass-loss prescriptions (Z^(0.41-1.4)) explored here overestimate the empirical
metallicity dependence in the B-
star regime, which appears very weak. We do not find an increase in mass-loss rate at approximately spectral type B1. We show that on average 40% of the wind mass is located in the wind medium between the clumps. We compiled a sample of 80+ O and B
stars in the SMC and LMC. From a comparison we find a clear difference in O- and B-type
metallicity dependence. Conclusions. The lack of a bi-stability jump in the B-
star regime and a weak
metallicity dependence for the same
stars offers new empirical constraints to models of line-driven winds. As differences between these models are large (reaching orders of magnitude) such constraints are much needed.
Read the full abstract ▾
All authors O. Verhamme, J.O. Sundqvist, A. de Koter, H. Sana, F. Backs, S. A. Brands, D. Debnath, N. Moens, P.Schillemans, C. Van der Sijpt, S. R. Berlanas, M. Bernini-Peron, P.A. Crowther, A. C. Gormaz-Matamala, R.Kuiper, C. Hawcroft, F. Najarro, D. Pauli, A.A.C. Sander, J.Th. van Loon, J.S. Vink, H. Todt, F. Tramper, Xshootu collaboration
Solar and Stellar Astrophysics
BV photometry of the ultracompact binary star GP Com
R. Zamanov, L. Dankova, M. Minev et al. (+2 more)
We present optical B and V band photometry of GP Com - an ultracompact binary consisting of an accreting white
dwarf and helium secondary component. Our data set contains 7.7 hours observations in V band with the 2.0m
telescope and 2.9 hours simultaneous observations in B and V bands with the 1.5m
telescope of the Rozhen National Astronomical Obsevatory, Bulgaria. The observations cover of about 13 orbital periods. We find an orbital modulation with amplitude 0.04-0.05 mag in B and V bands. Adopting that it is due to a bright spot, we estimate its temperature 19700 \pm 3000 K. We estimate mass
accretion rate onto the white
dwarf of about 2.10^{-12} M_sun/yr, consistent with the predicted rate for a cool donor. The data are available on Zenodo: zenodo.org/records/18768211.
Read the full abstract ▾
All authors R. Zamanov, L. Dankova, M. Minev, D. Boneva, K. Yankova
Solar and Stellar Astrophysics
Investigation of White-light Emission in Compact Flares
Yongliang Song
White-light
flares (WLFs) are usually tend to be those very large
flares. Nevertheless, several small and compact WLFs have been reported and thought to be produced by low-height
magnetic reconnection. However, whether low-height
magnetic reconnection can efficiently produce WLFs remains unclear. For the first time, we conduct a statistical study of the WL emission in compact
flares to address this question. Using over a decade observations from the
Solar Dynamics Observatory (SDO), we identify 28 compact
flares, including 19 C-class and 9 B-class
flares. We find these compact
flares can be classified into three types based on the
magnetic configuration of the
flare, corresponding to the U-shape loop (type I), the flux emergence near sunspot (type II), and the fan-spine like structure (type III). For each type, the
flares numbers are 9 (7 C-calss and 2 B-class), 9 (3 C-calss and 6 B-calss) and 10 (9 C-calss and 1 B-calss), respectively. We find the occurrence rate of WLFs in compact
flares is $\sim60.7\%$ (17/28), and for the C-class the rate can be up to $\sim89.5\%$ (17/19). No WLF was found in B-class compact
flares. The occurrence rates for three types are $\sim77.8\%$ (7/9), $\sim11.1\%$ (1/9) and 90% (9/10), respectively. And for the C-class
flares, the occurrence rates for three types are 100% (7/7), $\sim33.3\%$ (1/3) and 100% (9/9), respectively. Our results suggest type-I and type-III compact
flares are more likely to produce WL emissions.
Read the full abstract ▾
Astrophysics of Galaxies
SFUMATO#: A GPU-accelerated code for self-gravitational radiation hydrodynamics simulation with adaptive mesh refinement
Hajime Fukushima and Tomoaki Matsumoto
We present a new implementation of the SFUMATO code, called SFUMATO#, for solving self-gravitational radiation hydrodynamics problems using adaptive mesh refinement (AMR) with the CUDA/HIP programming frameworks. The code incorporates a multigrid solver for self-
gravity, radiation transfer with M1 closure and reduced speed of light approximation, non-
equilibrium chemistry, thermal
evolution, and sink particle schemes. We develop new non-
equilibrium chemistry and thermal solvers based on a linearized implicit method, whose accuracy is validated through a series of test problems by comparison with solutions obtained using the Newton-Raphson method. By incorporating the heat capacity of
dust grains, the
dust temperature can be evolved without iterative energy-balance calculations. From the perspective of computational cost, we demonstrate that adopting an increased pseudo
dust heat capacity accelerates the chemistry solver while preserving accuracy, even when the value is increased by up to three orders of magnitude relative to the realistic value. In addition, we perform a suite of test problems to confirm the validity of the other components of our implementation. The code supports multi-GPU execution via MPI-based parallelization. We measure the strong-scaling performance of the hydrodynamics and self-
gravity solvers on both uniform and AMR grids, as well as the overall code performance using a
giant molecular cloud simulation. We find that the computational cost of the self-
gravity solver increases with the number of MPI processes, indicating that efficient parallel performance is achieved only when the number of devices is chosen such that the cost of the self-
gravity solver remains comparable to that of the other components.
Read the full abstract ▾
Earth and Planetary Astrophysics · Cross-listed from physics.plasm-ph
Collisionless Phase Mixing Mimics Diffusive Transport in Radiation Belt Observations
Adnane Osmane, Xin An, Anton Artemyev et al. (+3 more)
Since the dawn of the space age, observations of energetic particles in planetary radiation belts have been interpreted within a diffusive transport framework, even though the dominant processes that populate and deplete these belts-such as injections and moon-driven absorption-produce highly structured, spatially localized particle distributions. This exposes a fundamental question: how can coherent phase-space structures evolving under collisionless dynamics give rise to observational signatures consistent with
diffusion-based transport? Here we show that
diffusion-like behaviour inferred from radiation belt observations can arise solely from an observational phase-mixing effect, independent of
stochastic wave-particle transport. As orbiting spacecraft sweep across neighbouring drift shells while trapped particles undergo electromagnetic drifts, measurements inevitably sample regions with slightly different drift frequencies. This converts localized drift-phase structures into rapidly decorrelating temporal signals, making them observationally indistinguishable from those produced by
stochastic wave-particle processes. We derive the associated correlation function analytically and show that the effective lifetime of these structures is only a few drift periods. Consequently, even highly localized injections rapidly lose coherence, preventing spacecraft from resolving fine-scale structure in the distribution function. These results show that collisionless dynamics can produce observational signatures that mimic diffusive transport on timescales shorter than those expected from radial transport, biasing inferred transport rates and long-term flux predictions. This calls for a reassessment of
diffusion-based interpretations from sparse in-situ measurements of radiation belts at Earth, across the
solar system, and in the recently discovered radiation belts of ultra-cool brown
dwarfs.
Read the full abstract ▾
All authors Adnane Osmane, Xin An, Anton Artemyev, Oliver Allanson, Jay Albert, Miroslav Hanzelka
Instrumentation and Methods for Astrophysics
Hill's level surfaces in the circular restricted three-body problem solved
Jean-Marc Huré
We report the closed-form expression for Hill's surfaces in the circular restricted three-body problem. The solution $\phi(r,\theta)$, derived in the primary-centric spherical coordinate system, is deduced from a cubic equation delivering at most two roots on each side of a separatrix. The famous patterns (tadpole, horseshoe and peanut shapes, Roche lobes and Hill's quasi-spheres) are exactly produced.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Energy Loss of Newborn Magnetars by Schwinger Process
Chul Min Kim, Sang Pyo Kim, Remo Ruffini et al. (+2 more)
We investigate electron–positron pair creation through the Schwinger process in newborn magnetars with millisecond
spin periods and surface dipole fields close to or above the QED critical field, $B_{\rm Q} = 4.414\times10^{13}\,\mathrm{G}$. In the unscreened field scenario, we derive the analytical global pair creation flux and recast it into a compact form with accurate analytic approximations. For a fiducial model with $B_{\rm p} = 10^{14}\,\mathrm{G}$ and $P_0 = 1\,\mathrm{ms}$, the Schwinger channel exceeds the classical Goldreich–Julian particle supply by many orders of magnitude and becomes the dominant source of charges at the earliest stage of the magnetar. The associated discharge removes about $90\%$ of the initial rotational energy within 30 ms, suppresses the gravitational-wave loss channel, and implies that the observable millisecond phase is extremely short in this unscreened scenario. The rapid energy release over such a short timescale may also provide a viable power source for astrophysical transients. Extending the same fiducial model to $10^4\,\mathrm{yr}$ gives
spin periods of order seconds, linking newborn millisecond magnetars to the mature magnetar population.
Read the full abstract ▾
All authors Chul Min Kim, Sang Pyo Kim, Remo Ruffini, Yu Wang, Shurui Zhang
Astrophysics of Galaxies
Supermassive Black Hole Winds in X-rays: SUBWAYS IV. Tracing Radio Emission and Unveiling the Role of Winds
E. Amenta, M. Brienza, G. Bruni et al. (+30 more)
Most Active
Galactic Nuclei (AGN) are
Radio Quiet, with
radio emission that may arise from
star-formation activity, AGN-driven winds, weak jets, and coronal activity. Disentangling these mechanisms is challenging and requires detailed multi-wavelength investigation, but it is crucial for quantifying AGN feedback in
galaxy evolution. We present a detailed
radio investigation of 21 X-ray selected AGN in the Supermassive Black Hole Winds in X-Rays (SUBWAYS) sample (log Lbol = 44.9-46.3 erg/s, z=0.1-0.5), selected to systematically search for Ultra-Fast
Outflows (UFOs). UFOs are detected in 30% of the targets, making the sample particularly well-suited for investigating the role and signatures of multi-scale
outflows at different frequencies. We build the
radio SED of the sources complementing our proprietary data, collected with the JVLA at 1.5 and 6 GHz, with images from LoTSS and other publicly available
radio surveys between 150 and 1400 MHz. We investigate the role and occurrence of the aforementioned mechanisms, with particular interest in
outflows and their possible relation with UFOs. We combined information on spectral indices, luminosities, and morphologies of the
radio emission with properties derived in other wavebands, such as
Star Formation Rate, X-ray luminosity, Eddington ratio or the UFO kinetic luminosity. All the sources are detected and are mostly consistent with RQ AGN. For 80% of the sources the data suggest the presence of an
outflow (wind or weak jet). Interestingly, our results indicate that AGN with UFOs tend to have larger
radio extension and a steep
radio spectrum consistent with
outflows. Moreover, the
radio emission of the 6 UFO hosts is consistent with predictions from wind-driven shock models, possibly indicating a direct connection between the two phases. Alternatively, this may reflect physical conditions favouring the rise of both phenomena.
Read the full abstract ▾
All authors E. Amenta, M. Brienza, G. Bruni, M. Brusa, R. Morganti, F. Panessa, R. D. Baldi, E. Behar, G. Lanzuisi, T. Shimwell, F. Tombesi, S. Bianchi, G. Chartas, A. Comastri, G. Cresci, B. De Marco, F. Fiore, M. Gaspari, V. E. Gianolli, R. Gilli, S. B. Kraemer, G. Kriss, Y. Krongold, F. La Franca, A. L. Longinotti, M. Mehdipour, E. Nardini, M. Perna, P. Petrucci, E. Piconcelli, G. Ponti, F. Ricci, L. Zappacosta
Solar and Stellar Astrophysics
A New Pathway to Single Be Stars: Ejected Companions from Type Ia Supernovae
Yuchen Bao, Zhenwei Li, Hongwei Ge et al. (+4 more)
Be
stars are rapid rotators generally produced by binary interactions. The single Be
stars in the observations pose challenges to the Be
star formation theory. In this paper, we propose a new pathway for the formation of single Be
stars, in which the Be
star is taken as the ejected companion
star from a Type Ia
supernova (SN Ia) explosion. Recent numerical simulations suggest that explosive oxygen burning, initiated via the convective Urca process in certain helium (He)
stars near the Chandrasekhar mass limit, can set off a SN Ia. Based on this proposition, we further demonstrate that about $0.4\%$ of He
star + main-sequence (MS)
star binaries may evolve into single Be
stars, where the MS
star is spun up due to the mass
accretion from the He
star, and then the He
star explodes as a SN Ia. We employ detailed binary evolutionary simulations and find the parameter space that would produce single Be
stars via the SN Ia channel. Around $22\%$ of Be
stars from the SN Ia progenitor channel exhibit peculiar tangential velocities exceeding $24\ \rm km/s$, classifying them as runaway
stars. This suggests that the SN Ia channel plays a meaningful role in forming single Be
stars, particularly within the runaway
star population.
Read the full abstract ▾
All authors Yuchen Bao, Zhenwei Li, Hongwei Ge, Hailiang Chen, Dengkai Jiang, Xuefei Chen, Zhanwen Han
High Energy Astrophysical Phenomena
A Synchronized Spin Model for Black-Hole Accretion Systems
Masahiro Morikawa and Akika Nakamichi
Black-hole
accretion systems exhibit a characteristic coexistence of activities: broad-band X-ray variability, hot coronae, wide-angle winds, and both steady and discrete jets. This coexistence suggests a persistently time-dependent
magnetic background in which noisy fluctuations and explosive release are both essential. In this paper, we connect them all to intermittent
magnetic reconnection and propose a Synchronized
Spin Model (SSM) in which multiple local dynamos in a rotating
accretion flow are represented as interacting macro-
spins. Their synchronization, partial synchronization, excursion, and reversal define a compact set of collective variables that organize both timing statistics and large-scale morphology. In this picture, multiscale
magnetic reconnection sustains coronal heating,
flares, intermittent
outflows, and discrete jet activity, while the same synchronization dynamics produce amplitude modulation and demodulation, providing a route to $1/f$-like variability, rms–flux/Taylor-like scaling, and approximately log-normal statistics of the demodulated envelope. We further argue that, although the continuous flux distribution in black-hole systems is more naturally discussed in multiplicative or log-normal terms, broader event-catalog statistics remain useful for describing suitably defined burst hierarchies, particularly by analogy with
solar and
stellar flare systems. The hard/soft cycle of X-ray binaries is then interpreted as motion through
magnetic state space.
Read the full abstract ▾
Solar and Stellar Astrophysics
Filter Design for Estimating the Stellar Metallicity of Metal-poor Stars from Gaia XP Spectra
Ruifeng Shi, Yang Huang, Kai Xiao et al. (+5 more)
The estimation of
stellar atmospheric parameters for large-scale samples, particularly metal-poor
stars, is a cornerstone of
Galactic archaeology. In this work, we optimized a photometric filter design tailored to measuring
stellar metallicities for very metal-poor
stars with [Fe/H]$< -1$.The optimal configurations consist of a central wavelength $\lambda_{\rm c}$ = 3960 Angstrom with a bandwidth $\Delta\lambda$ = 80 Angstrom for
giant stars, and $\lambda_{\rm c} $= 3920 Angstrom with $\Delta\lambda$ = 80 Angstrom for
dwarf stars. By applying these optimized filters to synthetic photometry derived from
Gaia XP spectra, we inferred
metallicities for both populations. Both internal and external validations demonstrate high precision across a wide
metallicity range: 0.18-0.19 dex for $-2 \le \rm [Fe/H] \le -1$, 0.23-0.33 dex for $-3 \le \rm [Fe/H] \le -2$, and approximately 0.39 dex for the most metal-poor regime, successfully extending down to $\rm [Fe/H] \approx -4$ for
giant stars, $\rm [Fe/H] \approx -3.3$ for
dwarf stars. Finally, we present a catalog of approximately 14.5 million metal-poor
stars with robust $\rm [Fe/H]$ measurements, along with more than ten thousand red
giant ultra metal-poor candidates with $\rm [Fe/H] < -4.0$, providing a valuable resource for exploring the early formation and chemical
evolution of the Milky Way.
Read the full abstract ▾
All authors Ruifeng Shi, Yang Huang, Kai Xiao, Chuanjie Zheng, Bowen Zhang, Hongrui Gu, Xinyi Li, Huiling Chen
High Energy Astrophysical Phenomena
Bayesian Inference of Dense-Matter Equations of State from Small-Radius Compact Stars with Twin-Star Scenarios
Xieyuan Dong, Hong Shen, Jinniu Hu et al. (+1 more)
We investigate dense-matter equations of state (EOSs) within a
Bayesian framework, with particular emphasis on whether recent small-radius compact-
star candidates can be accommodated in a twin-
star scenario. For the hadronic sector, we adopt a meta-modeling EOS constrained by the NICER mass–radius measurements of PSR J0030$+$0451, PSR J0437$-$4715, PSR J0614$-$3329, and the massive
pulsar PSR J0740$+$6620. The hadronic inference indicates that PSR J0614$-$3329 favors a somewhat softer EOS than the other two \(\sim1.4\,M_\odot\)
pulsars, while the \(\sim2\,M_\odot\) constraint prevents the EOS from becoming too soft. We then introduce a strong first-order phase transition through a constant-speed-of-sound
quark-matter segment. Using HESS J1731$-$347 and XTE J1814$-$338 to constrain the phase-transition parameters, we find a preferred transition density of \(n_\mathrm{t}\sim2.7\text{--}2.8\,n_0\), a sizable energy-density jump of \(600\text{--}700\) MeV, and a relatively large post-transition sound speed of \(c_s^2/c^2\sim0.85\). Such a phase transition generates a disconnected hybrid branch with radii of about \(6\text{--}7\) km at masses around \(1.2\text{--}1.4\,M_\odot\), and strongly suppresses the dimensionless
tidal deformability relative to the purely hadronic branch. This pronounced change in
tidal deformability is a characteristic signature of the twin-
star mechanism and may provide an important observational tool for identifying phase transitions in
neutron-
star matter in future multimessenger measurements. These results show that small-radius compact
stars can provide direct constraints on both the strength of a first-order phase transition and the stiffness of the post-transition phase in dense matter.
Read the full abstract ▾
All authors Xieyuan Dong, Hong Shen, Jinniu Hu, Ying Zhang
Earth and Planetary Astrophysics
Turbulent infall onto class 0 disks as cause of CAI brief condensation episode in the solar system
Jiachen Zheng, Xing Wei, Hongping Deng et al. (+2 more)
Calcium-aluminum-rich inclusions (CAIs) in carbonaceous chondritic meteorites are the oldest relics in the
solar system. Notably, their radiogenic age feature a brief (100 kyr) condensation episode. In contrast, the reservoirs of the short-lived isotopes in CAIs, presumably
supernovae or asymptotic
giant stars, pollutes
star-forming regions in
giant molecular cloud complexes (GMC) over much longer (Myr) duration. Through a series of numerical simulations, we show here the possibility that, within an extended region (2$\sim$3 AU), nearly all “pre-
solar” CAI-loaded grains in the infall clouds were sublimated and re-condensed during the early ($ \lesssim 10^5$ yr) infall and formation of class-0 disks. We adopt a set of initial conditions from a previous hydrodynamic simulation of the collapse of GMC and the formation of young
stellar clusters. We analyze the
evolution of the disk's thermal distribution and dynamical structure resulting from the interaction between circumstellar disks and infalling gas. Our follow-up simulations, with much higher resolution, show significant and rapid changes in the disk orientation and morphology due to the dynamic infall of external streamers. Warps and global spiral density waves commonly appear. They lead to intense dissipation which heats the gas to sufficiently high temperature to sublimate prior-generation CAIs. This solid-to-gas phase transition is followed by subsequent cooling and re-condensation. The CAI contained in the meteorites today could be the relics of the last episode of major infall onto class 0 disks.
Read the full abstract ▾
All authors Jiachen Zheng, Xing Wei, Hongping Deng, Wenrui Xu, Douglas N. C. Lin
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Phase transition structure of scalarized neutron stars: the effect of rotation and linear coupling
Kalin V. Staykov, Fethi M. Ramazanoğlu, Daniela D. Doneva et al. (+1 more)
There has been a recent revival in understanding the spontaneous scalarization phenomenon in scalar-tensor
gravity as a phase transition. Using the tools of the Landau theory, we now know that first-order transitions where scalarization occurs in a discontinuous manner is more prominent than what had been considered in the literature, and this might lead to novel observation channels. However, the examples so far have been restricted to specific quadratic scalar coupling terms and spherically symmetric
stars. Here we explore the phase transition structure of scalarization for more general couplings, considering linear as well as quadratic terms in the conformal scaling factor of the theory. Moreover, we also investigate the effect of rotation on the scalarization phase transition. Both of these considerations are natural choices since the coupling in a scalar-tensor theory can appear at all orders, and astrophysical
neutron stars commonly have angular momentum. The introduction of linear coupling leads to a complex solution space which is harder to explore. However, we demonstrate that the Landau model of scalarization enables us to systematically find the branches of scalarized solutions that are commonly overlooked in numerical searches, providing a novel tool. On the other hand, the main effect of
stellar rotation is shifting the
stellar masses at which the phase transition occurs to higher values, but the qualitative picture remains similar to what happens under spherical
symmetry.
Read the full abstract ▾
All authors Kalin V. Staykov, Fethi M. Ramazanoğlu, Daniela D. Doneva, Stoytcho S. Yazadjiev