arXiv subjects

Bernhard Müller

Publications and source records attributed to Bernhard Müller.

At least 19 recordsLinked to original sources

arXiv2026

Core-Collapse Supernovae and their Gravitational Wave Signals: The Status of Theory and Modeling

The detection of gravitational waves from a core-collapse supernova in the Milky Way or its vicinity represents a unique opportunity to probe the inner workings of these explosions. In this review, I briefly summarize our current understanding of the supernova explosion mechanism and then outline the physical processes that shape the supernova gravitational wave signal. The review highlights how the various components of the signal have the potential to constrain the progenitor rotation, the proto-neutron star structure, the nuclear equation of state, the nature of hydrodynamic instabilities, and the violence of turbulent motions in the supernova core. I also highlight some open questions and uncertainties in the theory of supernova gravitational wave astronomy as well as challenges for further progress. Specifically, there is a need to develop large model databases, systematic uncertainty quantification and methods for evidence assessment to prepare for multi-messenger observations from a Galactic supernova.

astro-ph.HE↗

arXiv2026

JWST observations of SN 2024abup: First Detection of CO in a broad-lined Type Ic Supernova and Constraints on r-process Nucleosynthesis

SN 2024abup is a nearby broad-lined Type Ic supernova (SN Ic-bl) in NGC 0681 at a distance of 23.3 \pm 1.6 Mpc. As energetic explosions of massive stars, SNe Ic-bl are considered a plausible site for rapid-neutron capture nucleosynthesis (r-process) and chemical enrichment from short-lived progenitors. They may also contribute to dust production in the early Universe. We present JWST near- to mid-infrared (NIR+MIR) observations (1-14 micron) of SN Ic-bl 2024abup at +41 days after the V band maximum (+54 days after explosion), the first-ever JWST+MIR observation of a SN Ic-bl along with radio and optical data. Using the spectral synthesis code SUMO, we identify the observed broad IR line features in SN 2024abup and find significant contributions from C, O, Mg, and carbon monoxide (CO) -- the earliest detection of molecules in a core-collapse SN so far. The spectrum shows continuum emission at wavelengths greater than 1.5 micron, which could be explained by dust -- preexisting, newly formed, or a combination-heated by the SN. We do not find compelling evidence for infrared signatures of r-process elements, though our search is hampered by the presence of many broad and blended features from the non-r-process elements. These new observations indicate that SNe Ic-bl could be a contributor to early-universe dust production, and suggest that if r-process elements are produced, revealing their presence from spectra requires very high-quality data and models to disentangle blends.

astro-ph.HE↗

arXiv2026

Impact of the nuclear equation of state on the explodability of massive stars

In recent years, astrophysical observations have placed tight constraints on key properties of the nuclear equation of state (EoS). Using 93 two-dimensional simulations for three different EoS compatible with the current tight constraints, we show that the EoS remains a major uncertainty for the outcome of core-collapse supernovae. Whereas explosions are obtained in most cases for the SFHo and SFHx EoS, for the CMF EoS, which includes a crossover from nucleonic matter to a quark phase, explosions occur only for 2 out of 15 progenitors. Less favourable conditions for neutrino-driven explosions arise for the CMF EoS due to lower neutrino luminosities and mean energies and slightly weaker contraction of the warm proto-neutron star. Our results suggest that the explodability of massive stars cannot yet be predicted based on first principles without better knowledge of the nuclear EoS. Conversely, observational constraints on stellar explodability may help further constrain the EoS.

astro-ph.HE↗

arXiv2026

Trends in gravitational wave emission in axisymmetric simulations of rotating core-collapse supernovae

The quantitative impact of strong rotation on the amplitudes and frequencies of the post-bounce gravitational wave (GW) signal from core-collapse supernovae (CCSNe) is still not fully understood. To study trends in frequencies and amplitudes, and possibly spectacular phenomena like resonant amplification, we perform a series of axisymmetric long-duration magnetohydrodynamic CCSN simulations of a 17 $M_\odot$ progenitor using a finely spaced grid in initial rotation rate from 0.29 rad/s to 3.48 rad/s. We find that these rotating models produce GWs at frequencies of up to 3 kHz, higher than in typical non-rotating models in the literature. The high frequencies arise due to small polar radii of rapidly rotating proto-neutron stars and stabilization by angular momentum gradients at lower latitude. GW frequencies and amplitudes tend to decrease with faster rotation. Different from two complementary simulations without magnetic fields, the magnetohydrodynamic models are characterized by an absence of p-modes above the dominant high-frequency emission band. We find no indication of resonant mode amplification for any rotation rate, although a temporo-spatial and space-frequency analysis reveals some interesting couplings of quadrupolar motions across the proto-neutron star and the gain region. Generalized, multi-dimensional perturbative techniques need to be developed to study the mode structure and mode interaction in the collapse of rapidly rotating massive stars.

astro-ph.HE↗

arXiv2026

The deci-Hz gravitational wave signal from the collapse of rotating very massive stars

We calculate the gravitational wave signal from the collapse of a rotating 300 $M_\odot$ star at the upper end of the pair-instability regime. The large-scale asymmetries that develop during the collapse produce a strong signal in the deci-Hz range that has a characteristic shape which is likely amenable to a template-based search. The most ambitious designs for deci-Hz detectors could detect such signals out to distances of 200 Mpc, possibly at a rate of 0.5 per year.

astro-ph.HE↗

arXiv2026

Resolution Dependence in Magnetohydrodynamic Simulations of Neutrino-Driven Core-Collapse Supernovae

We investigate the role of resolution and initial magnetic field strength on core-collapse supernovae in simulations of a non-rotating $13 \mathrm{M_\odot}$ progenitor. Specifically, we study the effect on shock revival, explosion dynamics, and the properties of the compact remnant. We run four models with different numerical grid resolutions with an initial central dipole field strength of $\mathord{\approx}10^{12}\, \mathrm{G}$. Two of those resolutions are also run with a weaker central magnetic field of $\mathord{\approx}10^{10}\, \mathrm{G}$ . The shock revival time for all models is largely independent of resolution and initial magnetic field strength, but we find higher explosion energies when the initial magnetism is stronger and at higher resolutions. We find that models with strong magnetic fields have lower neutrino luminosity and energies, due to a proto-neutron star (PNS) that is deformed by the strong magnetic fields. At higher resolutions, magnetic fields are amplified more efficiently in the gain region and in the PNS via the small-scale dynamo. Although the strong magnetic fields do not directly drive the explosion, they have a subsidiary impact on the explosion mechanism and compensate for the reduced neutrino heating. Stronger magnetic energies in the PNS also affect energy and angular momentum redistribution, leading to more extended and vigorous PNS convection zones at higher resolutions.

astro-ph.HE↗

arXiv2026

Angular momentum transport in the convection zone of a 3D MHD simulation of a rapidly rotating core-collapse progenitor

Rotation and magnetic fields in the cores of evolved massive stars in their final phase are thought to play an important role in the subsequent supernova explosion and the formation of a compact object, especially in hyperenergetic explosions. However, the interplay between rotation, magnetic fields, and convection up to the final collapse is a nonlinear, multidimensional effect that is difficult to capture with standard one-dimensional (1D) stellar evolution models. We quantify the magnetic angular momentum (AM) transport in the convective oxygen burning shell in a three-dimensional (3D) rotating core-collapse progenitor model. We find that the radial direction of magnetic AM transport is directly related to the Rossby number of the convective oxygen shell. We also analyze the magnetic energy, which sets the amplitude of the magnetic AM flux. The magnetic energy is determined both by rotation and the nuclear energy generation rate analogously to low-mass stars like the Sun. Based on these results, we construct a 1D model of magnetic AM transport in the convection zone for the first time in terms of properties of a given stellar evolution model. This model successfully reproduces the AM transport in the 3D model when the convective dynamo is in a quasi-steady state. Notably, our model for radial AM transport is the first to account for inward AM flux. This may result in interesting differences compared to the conventional treatment of magnetic AM transport in stellar evolution models, which assume AM is transported outward by a purely diffusive process.

astro-ph.SR↗

arXiv2025

Natal kicks of compact objects

When compact objects - neutron stars and black holes - are formed in a supernova explosion, they may receive a high velocity at formation, which may reach or even exceed 1000 km s-1 for neutron stars and hundreds of km s-1 for black holes. The origin of the velocity kick is intimately related to supernova physics. A better understanding of kick properties from astronomical observations will shed light on the unsolved problems of these explosions, such as the exact conditions leading to exotic electron capture and ultra-stripped supernovae. Kick velocities are profoundly important in several areas of astrophysics. Being a result of supernova explosions, the kick velocity distribution must be explained in the framework of the supernova mechanism. The kick magnitudes and directions influence many topics related to binary systems, including the rate of compact object coalescences observable through gravitational waves. Moreover, knowledge of the kick velocity distribution is significant in predicting future observational results and their interpretation. For example, it is expected that the Roman space telescope will discover many microlensing events related to neutron stars and black holes; accurate estimates of the number of observable microlensing events require precise kinematic properties of these compact objects.

astro-ph.HE↗

arXiv2025

Synthetic Light Curves and Spectra for the Photospheric Phase of a 3D Stripped-Envelope Supernova Explosion Model

We present synthetic light curves and spectra from three-dimensional (3D) Monte Carlo radiative transfer simulations based on a 3D core-collapse supernova explosion model of an ultra-stripped $3.5\,\mathrm{M}_{\odot}$ progenitor. Our calculations predict a fast and faint transient with $Δm_{15} \sim 1\texttt{-} 2\,\mathrm{mag}$ and peak bolometric luminosity between $-15.3\,\mathrm{mag}$ and $-16.4\,\mathrm{mag}$. Due to a large-scale unipolar asymmetry in the distribution of $^{56}\mathrm{Ni}$, there is a pronounced viewing-angle dependence with about $1\,\mathrm{mag}$ difference between the directions of highest and lowest luminosity. The predicted spectra for this rare class of explosions do not yet match any observed counterpart. They are dominated by prominent Mg~II lines, but features from O, C, Si, and Ca are also found. In particular, the O~I line at \wl{7}{774} appears as a blended feature together with Mg~II emission. Our model is not only faster and fainter than the observed Ib/c supernova population, but also shows a correlation between higher peak luminosity and larger $Δm_{15}$ that is not present in observational samples. A possible explanation is that the unusually small ejecta mass of our model accentuates the viewing-angle dependence of the photometry. We suggest that the viewing-angle dependence of the photometry may be used to constrain asymmetries in explosion models of more typical stripped-envelope supernova progenitors in future.

astro-ph.HE↗

arXiv2025

Gravitational waves from core-collapse supernovae with no electromagnetic counterparts

Core-collapse supernovae (CCSNe) are regularly observed electromagnetically, prompting targetted searches for their gravitational-wave emission. However, there are scenarios where these powerful explosions may not have any observable electromagnetic signal, but would still have strong detectable emission in gravitational waves and neutrinos. A regular CCSN explosion may be obscured by matter in the Galaxy. A star may undergo a failed CCSN explosion, where the stalled shockwave is not revived, and would eventually form a black hole. Higher mass progenitor stars may revive the shock, but form a black hole too quickly for the shockwave to reach the surface of the star and produce an electromagnetic signal. Previous work has shown that we can determine if a black hole forms from the CCSN neutrino emission if there are long duration sinusoidal modulations in the neutrino signal caused by the standing accretion shock instability (SASI). The SASI also produces an observable signature in the gravitational-wave emission. In this paper, we investigate if we can distinguish between different scenarios for electromagnetically dark CCSNe using the gravitational-wave emission alone. We find, using a reconstruction of the SASI mode, abrupt end times of the gravitational-wave emission, and the rate of change of frequency of the dominant mode, that we are able to accurately distinguish between an obscured CCSN, a failed CCSN, and an explosion with fast black hole formation.

astro-ph.HE↗

arXiv2025

Effects of multidimensional treatment of gravity in simulations on supernova gravitational waves

Supernova explosions are expected as one of the promising candidates for gravitational wave sources. In this study, we examine the supernova gravitational waves, focusing on the multidimensional treatment of gravity in the simulation. For this purpose, we newly performed two-dimensional relativistic simulations with a nonmonopole (two-dimensional) potential and compared the resultant gravitational wave signals in the simulations with the frequencies of the proto-neutron stars with and without the Cowling approximation. Then, we find that the proto-neutron star frequencies with the Cowling approximation overestimate the gravitational wave frequencies. On the other hand, the frequencies of the proto-neutron star oscillations with metric perturbations agree well with the gravitational wave signals in the simulations. Employing the new data, we derive a new fitting formula for the supernova gravitational wave frequencies with the two-dimensional gravitational potential, independently of the progenitor mass. Combining this new formula with the previous one derived from the Cowling approximation, we also derive the formula to predict the gravitational wave frequencies with a two-dimensional potential, using those with a monopole potential.

gr-qc↗

arXiv2025

The birth mass function of neutron stars

The birth mass function of neutron stars encodes rich information about supernova explosions, double star evolution, and properties of matter under extreme conditions. To date, it has remained poorly constrained by observations, however. Applying probabilistic corrections to account for mass accreted by recycled pulsars in binary systems to mass measurements of 90 neutron stars, we find that the birth masses of neutron stars can be described by a unimodal distribution that smoothly turns on at $1.1 M_{\odot}$, peaks at $1.27 M_{\odot}$, before declining as a steep power law. Such a ``turn-on" power-law distribution is strongly favoured against the widely-adopted empirical double-Gaussian model at the $3 σ$ level. The power-law shape may be inherited from the initial mass function of massive stars, but the relative dearth of massive neutron stars implies that single stars with initial masses greater than $\approx 18 M_{\odot}$ do not form neutron stars, in agreement with the absence of massive red supergiant progenitors to supernovae.

astro-ph.HE↗

arXiv2025

Core-collapse supernovae

Core-collapse supernovae (CCSNe) are the explosive end-points of stellar evolution for $M_{ZAMS} \gtrsim 8$ $M_\odot$ stars. The cores of these stars collapse to neutron stars, a process in which high neutrino luminosity drives off the overlying stellar layers, which get ejected with thousands of kilometers per second. These supernovae enrich their host galaxies with elements made both during the star's life and in the explosion, providing the main cosmic source of elements such as oxygen, neon and silicon. Their high luminosities ($\sim$ $10^{42}$ erg s$^{-1}$ at peak) make SNe beacons to large distances, and their light curves and spectra provide rich information on single and binary stellar evolution, nucleosynthesis, and a diverse set of high-energy physical processes. As the SN ejecta sweep up circumstellar and interstellar matter, it eventually enters a supernova remnant phase, exemplified by nearby, spatially resolved remnants such as Cas A and the Crab Nebula. In this phase, shocks and pulsar winds continue to light up the interior of the exploded stars, giving detailed information about their 3D structure. We review the central concepts of CCSNe, from the late stages of evolution of massive stars, through collapse, explosion, and electromagnetic display, to the final remnant phase. We briefly discuss still open questions, and current and future research avenues.

astro-ph.HE↗

arXiv2025

The minimum neutron star mass in neutrino-driven supernova explosions

Supernova theory has struggled to explain the lightest known neutron star candidate with an accurate mass determination, the $1.174\mathrm{M}_\odot$ companion in the eccentric compact binary system J0453+1559. To improve the theoretical lower limit for neutron star birth masses, we perform 3D supernova simulations for five stellar models close to the minimum mass for iron core collapse. We obtain a record-low neutron star mass of $1.192\mathrm{M}_\odot$ and a substantial kick of $\mathord{\sim} 100\,\mathrm{km}\,\mathrm{s}^{-1}$. Given residual uncertainties in stellar evolution, a neutron star origin for the $1.174\mathrm{M}_\odot$ object remains plausible.

astro-ph.HE↗

arXiv2024

Long-time 3D supernova simulations of non-rotating progenitors with magnetic fields

We perform five 3D magnetohydrodynamic (MHD) core-collapse supernova simulations for non-rotating progenitors between 9.5 $M_\odot$ and 24 $M_\odot$. Four of the five models produce explosions while one fails. The exploding models are extended to between 0.9 s and 1.6 s post-bounce to study a possible impact of magnetic fields on explosion and remnant properties. Diagnostic explosion energies grow at a similar pace as in previous non-magnetic models. They reach between 0.11 foe and 0.61 foe, but are still growing by the end of the simulations. Neutron star kicks reach no more than 300 km s$^{-1}$, and although these are also still growing, they are unlikely to be in conflict with observed pulsar velocities. Extrapolated neutron star spin periods are between 45 ms and 1.8 s, consistent with observed birth spin rates. Magnetic torques only contribute about 10% to the spin-up of the neutron star. The inclusion of magnetic fields does not provide a mechanism for spin-kick alignment in our simulations. Surface dipole fields are in the range of $10^{12}-10^{13}$ G, much smaller than the root-mean-square field strength. Different from previous simulations, magnetic fields in the gain region only reach at most O(1%) of kinetic equipartition, likely because relatively early shock revival cuts off accretion as a power source for field amplification, which appears to be driven primarily by shear flows at the bottom of the gain region.

astro-ph.HE↗

arXiv2024

Long-Time 2D Simulations of Fallback Supernovae: A Systematic Investigation of Explosions Dynamics and Mass Ejections

We present a set of eight fallback simulations of zero-metallicity progenitors with masses between $60 M_\odot$ and $95 M_\odot$. The simulations are computed in 2D with the general relativistic CoCoNuT-FMT code for the first few seconds after black hole formation, and then mapped to the Newtonian code Prometheus for long-duration simulations beyond shock breakout. All simulations produce successful explosions with final energies ranging from $0.41 \times 10^{51}$ erg to $2.5 \times 10^{51}$ erg and black hole masses from $20.7 M_\odot$ to $34.4 M_\odot$. Explosion energies and remnant masses do not vary monotonically with progenitor mass, but the mass cuts cluster near the outer edge of the helium core. A supplementary model with decreased neutrino heating provides a tentative indication that successful explosions require the shock to reach the sonic point in the infall profile by the time of black hole formation. The propagation of the shock to the surface is only approximately captured by proposed shock invariants, but these may still be sufficient to extrapolate the final black hole mass from the first seconds of evolution. We also discuss potential multi-messenger signatures of the predicted fallback explosions. The enrichment of the ejecta in intermediate mass and iron-group elements varies considerably and is non-neligible for the more powerful explosions. Low-level neutrino emission after black hole formation from these very massive progenitors may be detectable in the case of a Galactic event.

astro-ph.HE↗

arXiv2024

The gravitational-wave emission from the explosion of a 15 solar mass star with rotation and magnetic fields

Gravitational waveform predictions from 3D simulations of explosions of non-rotating massive stars with no magnetic fields have been extensively studied. However, the impact of magnetic fields and rotation on the core-collapse supernova gravitational-wave signal is not well understood beyond the core-bounce phase. Therefore, we perform four magnetohydrodynamical simulations of the explosion of a $15\,M_{\odot}$ star with the SFHx and SFHo equations of state. All of the models start with a weak magnetic field strength of $10^{8}$\,G, and two of the models are rapidly rotating. We discuss the impact of the rotation and magnetic fields on the gravitational-wave signals. We find that the weak pre-collapse fields do not have a significant impact on the gravitational-wave signal amplitude. With rapid rotation, the f/g-mode trajectory can change in shape, and the dominant emission band becomes broader. We include the low-frequency memory component of the gravitational-wave signal from both matter motions and neutrino emission anisotropy. We show that including the gravitational waves from anisotropic neutrino emission increases the supernova detection distances for the Einstein Telescope, and would also be detectable out to Mpc distances by a moon-based gravitational-wave detector.

astro-ph.HE↗

arXiv2024

Universality in supernova gravitational waves with proto-neutron star properties

Gravitational wave signals from core-collapse supernovae are one of the important observables for extracting the information of dense matter. To extract the properties of proto-neutron stars produced via core-collapse supernovae by asteroseismology, we perform a linear perturbation analysis using data obtained from two-dimensional numerical simulations. We employ 12 and 20 solar-mass progenitors and compare two different treatments of gravity. One is a general relativistic one with a conformal flatness condition and the other is an effective gravitational potential mimicking the Tolman-Oppenheimer-Volkoff solution. We discuss how the frequencies of the proto-neutron star oscillations corresponding to the gravitational wave signals in the simulations depend on the proto-neutron star properties. In our models, we find that the gravitational wave frequencies of the proto-neutron stars determined with the Cowling approximation can be expressed to very good approximation as a function of the proto-neutron star average density almost independently of the progenitor mass, treatment of gravity in the simulations, and the interpolations in the simulations. On the other hand, if one considers the gravitational wave frequencies as a function of the surface gravity of proto-neutron stars, such a relation appears sensitive to the treatment of gravity and other numerical details in the simulations. Thus, the average density of proto-neutron stars seems more suitable for universally expressing the supernova gravitational wave frequencies, instead of the surface gravity.

astro-ph.HE↗