Ore Gottlieb

The understanding of the mechanism(s) by which massive stars collapse and possibly explode is rapidly maturing. Uncertainties in the structure of the stellar core at the onset of collapse are often dominant in numerical simulations, and a limited number of progenitor grids are available. This is especially true for explosions where rotation and magnetic fields play a significant or primary role. We present a grid of 113 single-star models with initial masses M _ZAMS = 30–90 M _⊙ and initial rigid rotation ω _ZAMS = 0.5–0.99 ω _crit computed at Z = 0.001 with the open-source stellar evolution code MESA . We adopt a 128-isotope nuclear reaction network capable of following the weak reactions deleptonizing the core during and after silicon core burning. By construction, these models experience rotationally induced chemically homogeneous evolution, and reach the onset of collapse ( v _infall ≲ −300 km s ⁻¹ ) with large and structured amounts of angular momentum, possibly sufficient to form accretion disks on a protocompact object. Therefore, these progenitor structures provide a homogeneous set of models with updated input physics and improved algorithmic accuracy to understand stellar explosions of (some types of) stripped-envelope supernovae, possibly jetted and/or broad-lined, collapsars or magnetar-powered, and/or long gamma-ray bursts.

Kilohertz quasi-periodic oscillations (QPOs) have been observed in a few rare gamma-ray bursts (GRBs), but their physical origin remains uncertain. We reanalyze the two short GRBs with reported kilohertz QPOs, GRB 910711 and GRB 200415A, and find evidence for possible harmonic-like organization around a characteristic frequency scale near 360 hertz. The similar harmonic-like pattern in GRB 910711 and in the confirmed magnetar giant flare (MGF) event GRB 200415A, including features extending above 4 kilohertz, points to timing phenomenology on frequency scales relevant to magnetar oscillation modes. The temporal and spectral similarities between the two events and the difficulty of explaining these features in merger-driven scenarios favor an MGF-like interpretation of GRB 910711. This timing phenomenology may therefore provide an additional observational handle, complementary to spectral, temporal, and localization information, for distinguishing rare MGF-like transients from merger-driven GRBs.

We study spherical accretion onto primordial black holes (PBHs) embedded in the core of a solar-type star. We compute the radiative efficiency self-consistently for the first time across more than 6 decades in black hole mass (10 ^−16.5 –10 ⁻¹⁰ M _⊙ ) with time-dependent simulations, and follow the growth up to 10 ⁻² M _⊙ using an analytical photon-trapping prescription above 5 × 10 ⁻¹³ M _⊙ . Near the Schwarzschild radius ( r _S ∼ 10 ⁻¹¹ cm for a 10 ⁻¹⁶ M _⊙ PBH), gas compressed to T ∼ 10 ¹¹ K radiates through microphysical processes that fundamentally alter the classical adiabatic Bondi solution. We solve the time-dependent spherical Euler equations with an implicit cooling source term, determining M ̇ , the Bondi-normalized radiative efficiency η = L / ( M ̇ B c 2 ) , and the flow structure self-consistently. We identify three regimes for spherical accretion: a hot Bondi regime ( M _BH ≲ 10 ⁻¹⁴ M _⊙ ) in which bremsstrahlung cooling is dynamically negligible; a bremsstrahlung-cooling regime (10 ⁻¹⁴ –5 × 10 ⁻¹³ M _⊙ ) driving the flow toward isothermal with η ≈ 10 ⁻² ; and a photon-trapping regime above 5 × 10 ⁻¹³ M _⊙ , in which the Bondi sphere is optically thick and the accretion rate remains close to the Bondi value. Cooling enhances M ̇ by a factor of ∼1.5–7, keeping growth superexponential throughout the spherical regime. The radiative efficiency is an order of magnitude lower than previously assumed, and the critical initial PBH mass required to consume a solar-mass star within a Hubble time is M _0,crit ∼ 10 ⁻¹⁶ M _⊙ .

Recent discoveries of long gamma-ray bursts accompanied by kilonova emission have prompted interest in understanding their progenitors. If these long-duration bursts arise from neutron star mergers, similar to short gamma-ray bursts, it raises the question of which physical properties govern burst duration. The mass of the merger stands out as a key factor, strongly influencing the lifetime of the merger remnant, which in turn determines the burst duration: lighter mergers that form long-lived remnants produce short bursts, whereas more massive mergers result in short-lived remnants that collapse into black holes, powering longer bursts. In this paper, we compare merger rates from gravitational-wave observations of LIGO–Virgo–KAGRA with the rates of kilonova-associated long and short gamma-ray bursts to identify a characteristic total neutron star mass that separates the two burst classes at 1.3 6 − 0.09 + 0.08 times of the neutron star Tolman–Oppenheimer–Volkoff (TOV) mass (median and 68% confidence interval). This result suggests that massive neutron stars could survive an extended period after merger. Our findings are robust against substantial observational uncertainties and model assumptions. Moreover, we identify a correlation between the characteristic mass and the neutron star TOV mass, allowing constraints on the characteristic mass to be directly mapped to upper limits on the TOV mass. This establishes a novel, independent method for constraining the neutron star TOV mass and their equation of state using gravitational-wave and gamma-ray burst observations.

The origin of the large-scale poloidal magnetic field required to power relativistic jets in collapsars remains uncertain. While such a field may be inherited during proto-neutron-star collapse, the efficiency of this process is unclear, motivating an in situ mechanism to generate poloidal fields out of the predominantly toroidal fields produced by stellar differential rotation. We present the first 3D general-relativistic magnetohydrodynamics collapsar simulations initialized with toroidal magnetic field profiles that closely follow those of precollapse stellar models. As the toroidal field in the disk becomes dynamically important, it seeds the dynamo, producing coherent poloidal magnetic loops that appear at ∼ O ( 100 ) gravitational radii and are then advected inward along paths that may deviate from the disk midplane. The resulting poloidal fields thread the black hole (BH) and launch highly variable, wobbling relativistic jets on timescales of order seconds, with the onset depending on the initial magnetic field and the plasma circularization radius. Although the jets are highly variable and misaligned with the BH spin axis, they sustain ≳10 ⁵⁰ erg s ⁻¹ , comparable to that inferred for long gamma-ray bursts (LGRBs). We identify magnetic-flux inversions driven by the stochastic dynamo, leading to the formation of striped jets that could be imprinted in LGRB light curves. These results demonstrate that accretion-disk dynamos provide a robust pathway for jet production in collapsars across a broad range of progenitors.

We present the discovery of EP250827b/SN 2025wkm, an X-ray flash (XRF) discovered by the Einstein Probe (EP), accompanied by a broad-line Type Ic supernova (SN Ic-BL) at z = 0.1194. EP250827b possesses a prompt X-ray luminosity of ∼10 ⁴⁵ erg s ⁻¹ , lasts over 1000 s, and has a peak energy E _p < 1.5 keV at 90% confidence. SN 2025wkm possesses a double-peaked optical light curve (LC), though its bolometric luminosity plateaus after its initial peak for ∼20 days, consistent with a central engine injecting additional energy into the explosion. Its spectrum transitions from a blue to red continuum with clear blueshifted broad absorption features consistent with a SN Ic-BL classification. We do not detect any transient radio emission and rule out the existence of an on-axis, energetic jet ≳10 ⁵⁰ erg assuming a typical LGRB circumburst constant density ( n ≈ 10 ⁻³ –10 ⁻¹ cm ⁻³ ) and microphysical parameters ( ϵ _e = 0.1 and ϵ _B = 0.01). In the model we invoke, the collapse gives rise to a long-lived magnetar, potentially surrounded by an accretion disk. Magnetically driven winds from the magnetar and the disk mix together and break out with a velocity ∼0.35 c and interact with an extended circumstellar medium with radius ∼10 ¹³ cm, generating X-ray breakout emission through nonthermal free–free processes. The disk outflows and magnetar winds power blackbody photospheric emission as they cool adiabatically and thermalize, producing the first SN peak. The spin-down luminosity of the magnetar and radioactive decay of ⁵⁶ Ni power the late-time emission. We end by discussing the landscape of XRF-SNe within the context of EP’s recent discoveries.

GW231123, the most massive binary black hole (BH) merger observed to date, involves component BHs with masses inside the pair-instability mass gap and unusually high spins. This challenges standard formation channels such as classical stellar evolution and hierarchical mergers. However, stellar rotation and magnetic fields, which have not been systematically incorporated in prior models, can strongly influence the BH properties. We present the first self-consistent simulations tracking a massive, low-metallicity helium star from helium core burning through collapse, BH formation, and post-BH formation accretion using 3D general-relativistic magnetohydrodynamic simulations. Starting from a 250 M _⊙ helium core, we show that collapse above the pair-instability mass gap, aided by rotation and magnetic fields, drives mass loss through disk winds and jet launching. This enables the formation of highly spinning BHs within the mass gap and reveals a BH spin–mass correlation. Strong magnetic fields extract angular momentum from the BH through magnetically driven outflows, which in turn suppress accretion, resulting in slowly spinning BHs within the mass gap. In contrast, stars with weak fields permit nearly complete collapse and spin-up of the BH to a ≈ 1. We show that massive low-metallicity stars with moderate magnetic fields naturally produce BHs whose masses and spins match those inferred for GW231123, and are also consistent with those of GW190521. The outflows launched during collapse may impart a BH kick, which can induce spin–orbit misalignment and widen the postcollapse orbit, delaying the merger. These outflows could further drive short-lived, high-luminosity jets comparable to the most energetic γ -ray bursts, offering a potential observational signature of such events in the early Universe.

The Einstein Probe is revolutionizing time-domain astrophysics through the discovery of new classes of X-ray transients associated with broad-line Type Ic supernovae. These events commonly exhibit bright early-time optical counterparts and sudden afterglow rebrightening within the first week—features that existing models fail to explain. In particular, structured jet and cocoon scenarios are inconsistent with the observed sharp rebrightening and multiday optical emission, while the refreshed shock model is ruled out owing to its inconsistency with collapsar hydrodynamics. Drawing on 3D general relativistic magnetohydrodynamic simulations, we present the multiscale angular and radial structure characterizing collapsar outflows. The resulting morphology features episodic, wobbling jets with a “top-hat” geometry, embedded within a smoother global cocoon and disk ejecta angular structure. The wobbling jets give rise to variations in radiative efficiency that can account for the observed alternation between X-ray-dominated and γ-ray-dominated jet emission. The top-hat structure of individual wobbling jet episodes naturally explains the sudden rebrightening observed when the emission from the top-hat jet cores enters the observer’s line of sight. The radial structure is consistent with that inferred from observations of stripped-envelope supernovae. It comprises a mildly relativistic cocoon (0.3 ≲ βΓ ≲ 3) that may power an early (∼1 day) rapidly decaying emission, followed by slower, black-hole-accretion-disk-driven outflows (β ≲ 0.3), which dominate the slowly evolving optical emission at t ≳ 1 day. This novel multicomponent outflow structure provides a unified explanation for the multiband light curves observed in Einstein Probe transients and is likely a common feature of broad-line Type Ic supernovae more broadly.

Collapsars—rapidly rotating stellar cores that form black holes—can power gamma-ray bursts and are proposed to be key contributors to the production of heavy elements in the Universe via the rapid neutron capture process (r-process). Previous neutrino-transport collapsar simulations have been unable to unbind neutron-rich material from the disk. However, these simulations have not included sufficiently strong magnetic fields and the black hole (BH), both of which are essential for launching mass outflows. We present ν h-amr, a novel neutrino-transport general relativistic magnetohydrodynamic (νGRMHD) code, which we use to perform the first 3D global νGRMHD collapsar simulations. We find a self-consistent formation of a weakly magnetized dense accretion disk, which has sufficient time to neutronize. Eventually, substantial magnetic flux accumulates near the BH, becomes dynamically important, leads to a magnetically arrested disk (MAD), and unbinds some of the neutron-rich material. However, the strong flux also hinders accretion, lowers density, and increases neutrino-cooling timescale, which prevents further disk neutronization. Typical collapsar progenitors with mass accretion rates, M ̇ ∼ 0.1 − 1 M ⊙ s - 1 , do not produce significant neutron-rich (Y _e < 0.25) ejecta. However, we find that MADs at higher mass accretion rates, M ̇ ≳ few M ⊙ s - 1 (e.g., for more centrally concentrated progenitors), can unbind M _ej ≲ M _⊙ of neutron-rich ejecta. The outflows inflate a shocked cocoon that mixes with the infalling neutron-poor stellar gas and raises the final outflow Y _e; however, the final r-process yield may be determined earlier at the point of neutron capture freeze-out. Future work will explore under what conditions more typical collapsar engines become r-process factories.