Discovery of the Fastest Early Optical Emission from Overluminous SN Ia 2020hvf: A Thermonuclear Explosion within a Dense Circumstellar Environment

In this Letter we report a discovery of a prominent flash of a peculiar overluminous Type Ia supernova, SN 2020hvf, in about 5 hr of the supernova explosion by the first wide-field mosaic CMOS sensor imager, the Tomo-e Gozen Camera. The fast evolution of the early flash was captured by intensive intranight observations via the Tomo-e Gozen high-cadence survey. Numerical simulations show that such a prominent and fast early emission is most likely generated from an interaction between 0.01 M ⊙ circumstellar material (CSM) extending to a distance of ∼1013 cm and supernova ejecta soon after the explosion, indicating a confined dense CSM formation at the final evolution stage of the progenitor of SN 2020hvf. Based on the CSM–ejecta interaction-induced early flash, the overluminous light curve, and the high ejecta velocity of SN 2020hvf, we suggest that the SN 2020hvf may originate from a thermonuclear explosion of a super-Chandrasekhar-mass white dwarf (“super-M Ch WD”). Systematical investigations on explosion mechanisms and hydrodynamic simulations of the super-M Ch WD explosion are required to further test the suggested scenario and understand the progenitor of this peculiar supernova.

Thermonuclear explosion of a massive hybrid HeCO white-dwarf triggered by a He-detonation on a companion

Normal type Ia supernovae (SNe) are thought to arise from the thermonuclear explosion of massive (>0.8 M⊙) carbon-oxygen white dwarfs (WDs), although the exact mechanism is debated. In some models helium accretion on to a carbon-oxygen (CO) WD from a companion was suggested to dynamically trigger a detonation of the accreted helium shell. The helium detonation then produces a shock that after converging on itself close to the core of the CO-WD, triggers a secondary carbon detonation and gives rise to an energetic explosion. However, most studies of such scenarios have been done in one or two dimensions, and/or did not consider self-consistent models for the accretion and the He-donor. Here we make use of detailed 3D simulation to study the interaction of a He-rich hybrid 0.69 M⊙ HeCO WD with a more massive 0.8 M⊙ CO WD. We find that accretion from the hybrid WD on to the CO WD gives rise to a helium detonation. However, the helium detonation does not trigger a carbon detonation in the CO WD. Instead, the helium detonation burns through the accretion stream to also burn the helium shell of the donor hybrid HeCO-WD. The detonation of its massive helium shell then compresses its CO core, and triggers its detonation and full destruction. The explosion gives rise to a faint, likely highly reddened transient, potentially observable by the Vera Rubin survey, and the high-velocity (∼1000 kms−1) ejection of the heated surviving CO WD companion. Pending on uncertainties in stellar evolution we estimate the rate of such transient to be up to $\sim 10{{\ \rm per\ cent}}$ of the rate of type Ia SNe.

A closer look at non-interacting He stars as a channel for producing the old population of type Ia supernovae

The nature of the progenitors of type Ia supernovae (SNe Ia) remains a mystery. Binary systems consisting of a white dwarf (WD) and a main-sequence (MS) donor are potential progenitors of SNe Ia, in which a thermonuclear explosion of the WD may occur when its mass reaches the Chandrasekhar limit during accretion of material from a companion star. In the present work, we address theoretical rates and delay times of a specific MS donor channel to SNe Ia, in which a helium (He) star + MS binary produced from a common envelope event subsequently forms a WD + MS system without the He star undergoing mass transfer by Roche lobe overflow. By combining the results of self-consistent binary evolution calculations with population synthesis models, we find that the contribution of SNe Ia in this channel is around 2.0 × 10−4 yr−1. In addition, we find that delay times of SNe Ia in this channel cover a range of about 1.0–2.6 Gyr, and almost all SNe Ia produced in this way (about 97%) have a delay time of ≳1 Gyr. While the rate of SN Ia in this work is about 10% of the overall SN Ia rate, the channel represents a possible contribution to the old population (1–3 Gyr) of observed SNe Ia.

Strategic surprise, nuclear proliferation and US foreign policy

What are the effects of strategic surprise on foreign policy? We apply mechanisms from cognitive psychology and foreign policy analysis — the hindsight bias and policy engagement — to theorize about how political leaders attribute blame for strategic surprises and the consequences for their foreign policies. We argue that leaders who are hardly engaged with policy matters related to a surprise will tend to believe that it should have been foreseen, attribute blame to domestic culprits and favour significant changes in foreign policy. Conversely, those more involved with policy planning will blame an adversary’s deception and resist policy change. We illustrate these hypotheses empirically by examining the cases of the Truman administration’s reaction to the 1949 Soviet nuclear test and the Johnson administration’s reaction to the 1967 Chinese thermonuclear explosion. Despite their similar international and domestic political environments, the two presidents reacted quite differently to the two surprises. Truman, who was weakly engaged with nuclear matters prior to 1949, authorized major policy changes and reorganized the Central Intelligence Agency. Conversely, Johnson’s deeper involvement in nuclear matters led him to attribute blame for the surprise to Chinese deception. He sought to use the 1967 test to advance his ongoing efforts to secure the nuclear non-proliferation treaty. The findings suggest that the variables of policy engagement and the hindsight bias can predict how leaders’ foreign policies will respond to surprises regarding nuclear weapons proliferation and potentially other shifts in the balance of power.

Sensitivity of Type Ia supernovae to electron capture rates

The thermonuclear explosion of massive white dwarfs is believed to explain at least a fraction of Type Ia supernovae (SNIa). After thermal runaway, electron captures on the ashes left behind by the burning front determine a loss of pressure, which impacts the dynamics of the explosion and the neutron excess of matter. Indeed, overproduction of neutron-rich species such as 54Cr has been deemed a problem of Chandrasekhar-mass models of SNIa for a long time. I present the results of a sensitivity study of SNIa models to the rates of weak interactions, which have been incorporated directly into the hydrodynamic explosion code. The weak rates have been scaled up or down by a factor ten, either globally for a common bibliographical source, or individually for selected isotopes. In line with previous works, the impact of weak rates uncertainties on sub-Chandrasekhar models of SNIa is almost negligible. The impact on the dynamics of Chandrasekhar-mass models and on the yield of 56Ni is also scarce. The strongest effect is found on the nucleosynthesis of neutron-rich nuclei, such as 48Ca, 54Cr, 58Fe, and 64Ni. The species with the highest influence on nucleosynthesis do not coincide with the isotopes that contribute most to the neutronization of matter. Among the latter, there are protons, 54, 55Fe, 55Co, and 56Ni, while the main influencers are 54, 55Mn and 55 − 57Fe, in disagreement with Parikh et al (2013, A&A, 557, A3), who found that SNIa nucleosynthesis is most sensitive to the β+-decay rates of 28Si, 32S, and 36Ar. An increase in all weak rates on pf-shell nuclei would affect the dynamical evolution of burning bubbles at the beginning of the explosion and the yields of SNIa.

Theory of The Three Fields of Space

This article is a logical and rational analysis of the physical phenomena produced by the three fields that are generated in space: gravity field; field of terrestrial nuclear magnetism; and orbital field. Eduardo Guimarães, through the studies of the three nuclear masses of the Sun's nucleus, the three nuclear masses of the moon's nucleus, and the three nuclear masses of the Earth's nucleus. We discover the three spatial fields that are generated in the solar system and in the planets. Then, from the general theory of the three fields of space, we can understand all the mechanics that generate the dynamics and kinematics of celestial bodies. So now we can understand why the smaller celestial bodies orbit the orbital field of the largest celestial bodies. So now we can understand why the planets produce orbits of elliptical motions, around the orbital field of the Sun. Then we understand the orbital mechanics of the little planet Mercury, and its abnormal orbit around the orbiting field of the Sun. Then Mercury has a perihelion precession of 2 degrees per century, due to an approximation of the perihelion of Mercury which is attracted by the micro-gravity of the Sun, generating an orbital deviation of 2 degrees per century. In the future the planet Mercury will lose energy from its nucleus and will not be able to make the orbital curve of the perihelion because it will have been attracted by the gravitational field of the Sun's nucleus. The fall of Mercury on the Sun will generate two thermonuclear explosions of SUPERNOVA. The first thermonuclear explosion of SUPERNOVA will be generated by the thermonuclear collision of the gravity mass attraction of Mercury debris with the Sun's nucleus. The second thermonuclear explosion of SUPERNOVA will be generated by the thermonuclear collision of attraction of the mass of orbital attraction of Mercury debris with the nucleus of the Sun. These two thermonuclear explosions of SUPERNOVA will generate two immense thermonuclear shockwaves that will devastate the entire fragile geo-biome of the solar system.

Thermonuclear burst oscillations and the dense matter equation of state

Matter in neutron star cores reaches extremely high densities, forming states of matter that cannot be generated in the laboratory. The Equation of State (EOS) of the matter links to macroscopic observables, such as mass M and radius R, via the stellar structure equations. A promising technique for measuring M and R exploits hotspots (burst oscillations) that form on the stellar surface when material accreted from a companion star undergoes a thermonuclear explosion. As the star rotates, the hotspot gives rise to a pulsation, and relativistic effects encode information about M and R into the pulse profile. However the burst oscillation mechanism remains unknown, introducing uncertainty when inferring the EOS. I review the progress that we are making towards cracking this long-standing problem, and establishing burst oscillations as a robust tool for measuring M and R. This is a major goal for future large area X-ray telescopes.