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Register a new userProbing the progenitors of spinning binary black-hole mergers with long gamma-ray bursts
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Long gamma-ray bursts are associated with the core-collapse of massive, rapidly spinning stars. However, the believed efficient angular momentum transport in stellar interiors leads to predominantly slowly-spinning stellar cores. Here, we report on binary stellar evolution and population synthesis calculations, showing that tidal interactions in close binaries not only can explain the observed sub-population of spinning, merging binary black holes, but also lead to long gamma-ray bursts at the time of black-hole formation, with rates matching the empirical ones. We find that $approx$10% of the GWTC-2 reported binary black holes had a long gamma-ray burst associated with their formation, with GW190517 and GW190719 having a probability of $approx$85% and $approx$60%, respectively, being among them.
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We review the main physical processes that lead to the formation of stellar binary black holes (BBHs) and to their merger. BBHs can form from the isolated evolution of massive binary stars. The physics of core-collapse supernovae and the process of common envelope are two of the main sources of uncertainty about this formation channel. Alternatively, two black holes can form a binary by dynamical encounters in a dense star cluster. The dynamical formation channel leaves several imprints on the mass, spin and orbital properties of BBHs.
We consider a scenario for the longest duration gamma ray bursts, resulting from the collapse of a massive star in a close binary system with a companion black hole. The primary black hole born during the core collapse is spun up and increases its mass during the fallback of the stellar envelope. The companion black hole provides an additional angular momentum to the envelope, which ultimately makes the core BH spinning with a high Kerr parameter. After the infall and spiral-in, the two black holes merge inside the circumbinary disk. The second episode of mass accretion and final, even larger spin of the post-merger black hole prolongs the gamma ray burst central engine activity. The observed events should have two distinct peaks in the electromagnetic signal, separated by the gravitational wave emission. The gravitational recoil of the burst engine is also possible.
We aim to study the progenitor properties and expected rates of the two lowest-mass binary black hole (BH) mergers, GW 151226 and GW 170608, detected within the first two Advanced LIGO-Virgo runs, in the context of the isolated binary-evolution scenario. We use the public MESA code, which we adapted to include BH formation and unstable mass transfer developed during a common-envelope (CE) phase. Using more than 60000 binary simulations, we explore a wide parameter space for initial stellar masses, separations, metallicities, and mass-transfer efficiencies. We obtain the expected distributions for the chirp mass, mass ratio, and merger time delay by accounting for the initial stellar binary distributions. Our simulations show that, while the progenitors we obtain are compatible over the entire range of explored metallicities, they show a strong dependence on the initial masses of the stars, according to stellar winds. All the progenitors follow a similar evolutionary path, starting from binaries with initial separations in the $30-200~R_odot$ range, experiencing a stable mass transfer interaction before the formation of the first BH, and a second unstable mass-transfer episode leading to a CE ejection that occurs either when the secondary star crosses the Hertzsprung gap or when it is burning He in its core. The CE phase plays a fundamental role in the considered low-mass range: only progenitors experiencing such an unstable mass-transfer phase are able to merge in less than a Hubble time. We find integrated merger-rate densities in the range $0.2-5.0~{rm yr}^{-1}~{rm Gpc}^{-3}$ in the local Universe for the highest mass-transfer efficiencies explored. The highest rate densities lead to detection rates of $1.2-3.3~{rm yr}^{-1}$, being compatible with the observed rates. A high CE-efficiency scenario with $alpha_{rm CE}=2.0$ is favored when comparing with observations. ABRIDGED.
We consider some general implications of bright gamma-ray counterparts to fast radio bursts (FRBs). We show that even if these manifest in only a fraction of FRBs, gamma-ray detections with current satellites (including Swift) can provide stringent constraints on cosmological FRB models. If the energy is drawn from the magnetic energy of a compact object such as a magnetized neutron star, the sources should be nearby and be very rare. If the intergalactic medium is responsible for the observed dispersion measure, the required gamma-ray energy is comparable to that of the early afterglow or extended emission of short gamma-ray bursts. While this can be reconciled with the rotation energy of compact objects, as expected in many merger scenarios, the prompt outflow that yields the gamma-rays is too dense for radio waves to escape. Highly relativistic winds launched in a precursor phase, and forming a wind bubble, may avoid the scattering and absorption limits and could yield FRB emission. Largely independent of source models, we show that detectable radio afterglow emission from gamma-ray bright FRBs can reasonably be anticipated. Gravitational wave searches can also be expected to provide useful tests.
Binary black hole mergers are of great interest to the astrophysics community, not least because of their promise to test general relativity in the highly dynamic, strong field regime. Detections of gravitational waves from these sources by LIGO and Virgo have garnered widespread media and public attention. Among these sources, precessing systems (with misaligned black-hole spin/orbital angular momentum) are of particular interest because of the rich dynamics they offer. However, these systems are, in turn, more complex compared to nonprecessing systems, making them harder to model or develop intuition about. Visualizations of numerical simulations of precessing systems provide a means to understand and gain insights about these systems. However, since these simulations are very expensive, they can only be performed at a small number of points in parameter space. We present binaryBHexp, a tool that makes use of surrogate models of numerical simulations to generate on-the-fly interactive visualizations of precessing binary black holes. These visualizations can be generated in a few seconds, and at any point in the 7-dimensional parameter space of the underlying surrogate models. With illustrative examples, we demonstrate how this tool can be used to learn about precessing binary black hole systems.
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