Three-dimensional GRMHD simulations of jet formation and propagation in self-gravitating collapsing stars

TL;DR

This study advances collapsar modeling by performing 3D GRMHD simulations with evolving spacetime that includes self-gravity as a perturbative Kerr–Schild correction. By comparing self-gravitating and non-self-gravitating runs under identical initial conditions, it demonstrates that self-gravity can cause temporary jet quenching, reduce jet opening angles, accelerate black-hole mass and spin evolution, and disrupt the MAD state, potentially yielding quiescent intervals or failed GRBs. The results indicate that self-gravity narrows the range of initial conditions that produce successful, energetic jets and offers a mechanism to explain certain features of GRB prompt emission variability. Overall, the work highlights the importance of dynamical gravity in central-engine physics and jet phenomenology for long-duration GRBs.

Abstract

We investigate collapsar models with and without self-gravity under identical initial conditions to directly compare the effects of self-gravity on jet properties, such as opening angle, jet power, terminal Lorentz factor, and its variability. We compute a suite of time-dependent, three-dimensional GRMHD simulations of collapsars in evolving spacetime. We update the Kerr metric components due to the growth of the black hole mass and changes its angular momentum. The self-gravity is considered via perturbative terms. We present for the first time the process of jet formation in self-gravitating collapsars. We find that self-gravity leads to temporary jet quenching, which can explain some features in the gamma-ray burst prompt emission. We find no substantial difference in jet launching times between models with and without self-gravity. We observe that in the absence of self-gravity, the jet can extract more rotational energy from the black hole, while self-gravitating models produce narrower jet opening angles. We show that under certain conditions, self-gravity can interrupt the jet formation process, resulting in a failed burst. Our computations show that self-gravity significantly modifies the process of jet propagation, resulting in notably different jet properties. We show that the timescales, variability, and opening angle of jet depend on whether self-gravity is included or not. We argue that self-gravity can potentially explain certain prompt emission properties due to the jet quenching.

Figures (6)

• Figure 1: Evolution of the terminal Lorentz factor ($\Gamma_{\infty}$) for Model-1 (left) and Model-2 (right).
• Figure 2: Jet opening angle for Model-1 (top), and for Model-1-NSG and Model-2-NSG (bottom), obtained using two methods.
• Figure 3: Evolution of the black hole spin, mass and accretion rate for Model-1 (top) and Model-2 (bottom).
• Figure 4: Dimensionless magnetic flux ($\phi_{\rm MAD}$) and emission efficiency ($\eta$) for Model-1 and Model-2.
• Figure 5: Two-dimensional maps of magnetization ($\sigma$) and terminal Lorentz factor ($\Gamma_{\infty}$), and equatorial-plane map of rest-mass density ($\rho$) with overlaid magnetic field lines for Model-1-SG. Columns show $t = 0.074$, $0.111$, and $0.140\,\mathrm{s}$.