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Collision course SN 2006gy is an extremely luminous super-nova explosion, perhaps a hundred times more energetic than a typical supernova arising from the collapse of the core of a massive star. Current theories suggest that its progenitor was a star more than 100 times the mass of the Sun. That conclusion is at odds with the supernova's spectrum, which indicates the presence of a hydrogen envelope that would have been lost by a massive star long before the explosion. Two groups now present evidence to support alternative explanations for this supernova, both involving collision. Simon Portegies Zwart and Edward van den Heuvel show that the collision frequency of massive stars in a dense young cluster is sufficient to cause an explosion of the scale of SN 2006gy. And Woosley et al . present a model that explains the brightest supernovae as products of collisions between shells of matter ejected by massive stars made unstable by the production of electron–positron pairs. This paper reports that the brightest supernovae arise from collisions between shells of matter ejected by massive stars. An electron-positron 'pair instability' leads to explosive burning that ejects many solar masses of material. When the next explosion occurs, several solar masses of material are again ejected, which collide with the earlier ejecta, radiating 10 50 erg of light. The extremely luminous supernova SN 2006gy (ref. 1 ) challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too luminous by more than a factor of ten. Here we report that the brightest supernovae in the modern Universe arise from collisions between shells of matter ejected by massive stars that undergo an interior instability arising from the production of electron–positron pairs 2 . This ‘pair instability’ leads to explosive burning that is insufficient to unbind the star, but ejects many solar masses of the envelope. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 10 50  erg of light, about a factor of ten more than an ordinary supernova. Our model is in good agreement with the observed light curve for SN 2006gy and also shows that some massive stars can produce more than one supernova-like outburst.

Proposed mechanisms for the production of calcium in the first stars (population III stars)—primordial stars that formed out of the matter of the Big Bang—are at odds with observations 1 . Advanced nuclear burning and supernovae were thought to be the dominant source of the calcium production seen in all stars 2 . Here we suggest a qualitatively different path to calcium production through breakout from the ‘warm’ carbon–nitrogen–oxygen (CNO) cycle through a direct experimental measurement of the 19 F( p ,  γ ) 20 Ne breakout reaction down to a very low energy point of 186 kiloelectronvolts, reporting a key resonance at 225 kiloelectronvolts. In the domain of astrophysical interest 2 , at around 0.1 gigakelvin, this thermonuclear 19 F( p ,  γ ) 20 Ne rate is up to a factor of 7.4 larger than the previous recommended rate 3 . Our stellar models show a stronger breakout during stellar hydrogen burning than previously thought 1 , 4 , 5 , and may reveal the nature of calcium production in population III stars imprinted on the oldest known ultra-iron-poor star, SMSS0313-6708 6 . Our experimental result was obtained in the China JinPing Underground Laboratory 7 , which offers an environment with an extremely low cosmic-ray-induced background 8 . Our rate showcases the effect that faint population III star supernovae can have on the nucleosynthesis observed in the oldest known stars and first galaxies, which are key mission targets of the James Webb Space Telescope 9 . Observation of a new resonance in the 19-fluorine to 20-neon thermonuclear reaction at the China JinPing Underground Laboratory (over 2 km below ground) may provide clues to observed discrepancies in calcium production in the evolution of the first stars.

Up to now, more than 62 of the 115 X-ray sources of low-mass-X-ray binaries have been identified as photospheric radius expansion (PRE) bursters [1]. Galloway and collaborators expect more PRE bursters in their near future analysis [2]. Although more than half of the discovered X-ray sources are PRE bursters, the bursting mechanism of PRE burster is still not adequately understood. This is because of the complicated hydrodynamics and variable accretion rates. An example is the accretion-powered millisecond pulsar SAX J1808.4–3658 [3, 4] that powered up the brightest Type-I X-ray burst (XRB) recorded by NICER in recent history [5]. The first 1D multi-zone model of SAX J1808.4–3658 was recently constructed [6, 7]. The pioneering model offers a first concurrent and direct comparison with the observed light curves, fluences, and recurrence times. With the three observables, a comparison between theory and observations could be more sensitive than the previous studies of the clocked burster and post-processing models. We perform a sensitivity study on ( α ,p), ( α , γ ), (p, α ), and (p, γ ) reactions with a total up to ~1,500 reactions. Our current result indicates that the observables are more sensitive to the competition between the reactions involving alpha-capture, e.g., the 22 Mg( α , p) and 22 Mg(p, γ ) reactions competing at the 22 Mg branch point [8].

About 4.6 billion years ago, some event disturbed a cloud of gas and dust, triggering the gravitational collapse that led to the formation of the solar system. A core-collapse supernova, whose shock wave is capable of compressing such a cloud, is an obvious candidate for the initiating event. This hypothesis can be tested because supernovae also produce telltale patterns of short-lived radionuclides, which would be preserved today as isotopic anomalies. Previous studies of the forensic evidence have been inconclusive, finding a pattern of isotopes differing from that produced in conventional supernova models. Here we argue that these difficulties either do not arise or are mitigated if the initiating supernova was a special type, low in mass and explosion energy. Key to our conclusion is the demonstration that short-lived 10 Be can be readily synthesized in such supernovae by neutrino interactions, while anomalies in stable isotopes are suppressed. One hypothesis for solar system formation is gas compression by a nearby supernova, whose traces should be found in isotopic anomalies. Here the authors show that this mechanism is viable only if the triggering event was a low-mass supernova, looking at short-lived 10Be and lack of anomalies in stable isotopes.

We summarize our studies on neutrino-driven nucleosynthesis in He shells of early core-collapse supernovae with metallicities of Z ≲ 10−3 Z⊙. We find that for progenitors of ∼ 11–15 M⊙, the neutrons released by 4He(e, e+n)3H in He shells can be captured to produce nuclei with mass numbers up to A ∼ 200. This mechanism is sensitive to neutrino emission spectra and flavor oscillations. In addition, we find two new primary mechanisms for neutrino-induced production of 9Be in He shells. The first mechanism produces 9Be via 7Li(n,γ)8Li(n,γ)9Li(e− e)9Be and relies on a low explosion energy for its survival. The second mechanism operates in progenitors of ∼ 8 M⊙, where 9Be can be produced directly via 7Li(3H, n0)9Be during the rapid expansion of the shocked Heshell material. The light nuclei 7Li and 3H involved in these mechanisms are produced by neutrino interactions with 4He. We discuss the implications of neutrino-induced nucleosynthesis in He shells for interpreting the elemental abundances in metal-poor stars.

In Type-I X-ray bursts (XRBs), the rapid-proton capture (rp-) process passes through the NiCu and ZnGa cycles before reaching the region above Ge and Se isotopes that hydrogen burning actively powers the XRBs. The sensitivity study performed by Cyburt et al. [1] shows that the 57Cu(p,γ)58Zn reaction in the NiCu cycles is the fifth most important rp-reaction influencing the burst light curves. Langer et al. [2] precisely measured some low-lying energy levels of 58Zn to deduce the 57Cu(p,γ)58Zn reaction rate. Nevertheless, the order of the 1+1 and 2+3 resonance states that dominate at 0:2 ≲ T(GK) ≲ 0:8 is not confirmed. The 1+2 resonance state, which dominates at the XRB sensitive temperature regime 0:8 ≲ T(GK) ≲ 2 was not detected. Using isobaric-multipletmass equation (IMME), we estimate the order of the 1+1 and 2+3 resonance states and estimate the lower limit of the 1+2 resonance energy. We then determine the 57Cu(p,γ)58Zn reaction rate using the full pf -model space shell model calculations. The new rate is up to a factor of four lower than the Forstner et al. [3] rate recommended by JINA REACLIBv2.2. Using the present 57Cu(p,γ)58Zn, the latest 56Ni(p,γ)57Cu and 55Ni(p,γ)56Cu reaction rates, and 1D implicit hydrodynamic Kepler code, we model the thermonuclear XRBs of the clocked burster GS 1826–24. We find that the new rates regulate the reaction flow in the NiCu cycles and strongly influence the burst-ash composition. The 59Cu(p,γ)56Ni and 59Cu(p,α)60Zn reactions suppress the influence of the 57Cu(p,γ)58Zn reaction. They strongly diminish the impact of the nuclear reaction flow that bypasses the 56Ni waiting point induced by the 55Ni(p,γ)56Cu reaction on burst light curve.

When massive stars die as supernovae, these explosions can be seen out to the 'edge of the Universe'. But the stars' nature is often unclear. New observations provide insight into the life of one such star before it exploded. See Letter p.65 Energetic mass loss precedes supernova explosion Various lines of evidence suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae. This paper reports the observation of one such event: 40 days before the explosion of the type IIn supernova SN 2010mc its progenitor underwent an energetic outburst that released 0.01 solar masses of material at velocities of around 2,000 km per second.The luminosity and velocity of the outburst are consistent with the predictions of the wave-driven pulsation model of supernova explosions.

The most massive and shortest-lived stars dominate the chemical evolution of the pre-galactic era. On the basis of numerical simulations, it has long been speculated that the mass of such first-generation stars was up to several hundred solar masses 1 – 4 . The very massive first-generation stars with a mass range from 140 to 260 solar masses are predicted to enrich the early interstellar medium through pair-instability supernovae (PISNe) 5 . Decades of observational efforts, however, have not been able to uniquely identify the imprints of such very massive stars on the most metal-poor stars in the Milky Way 6 , 7 . Here we report the chemical composition of a very metal-poor (VMP) star with extremely low sodium and cobalt abundances. The sodium with respect to iron in this star is more than two orders of magnitude lower than that of the Sun. This star exhibits very large abundance variance between the odd- and even-charge-number elements, such as sodium/magnesium and cobalt/nickel. Such peculiar odd–even effect, along with deficiencies of sodium and α elements, are consistent with the prediction of primordial pair-instability supernova (PISN) from stars more massive than 140 solar masses. This provides a clear chemical signature indicating the existence of very massive stars in the early universe. The chemical composition of the Galactic halo star J1010+2358 shows extremely low sodium and cobalt abundances, different from most other halo stars, indicative of a very metal-poor star being seeded with elements from a pair-instability supernova.

All stellar-mass black holes have hitherto been identified by X-rays emitted from gas that is accreting onto the black hole from a companion star. These systems are all binaries with a black-hole mass that is less than 30 times that of the Sun 1 – 4 . Theory predicts, however, that X-ray-emitting systems form a minority of the total population of star–black-hole binaries 5 , 6 . When the black hole is not accreting gas, it can be found through radial-velocity measurements of the motion of the companion star. Here we report radial-velocity measurements taken over two years of the Galactic B-type star, LB-1. We find that the motion of the B star and an accompanying Hα emission line require the presence of a dark companion with a mass of 68 − 13 + 11 solar masses, which can only be a black hole. The long orbital period of 78.9 days shows that this is a wide binary system. Gravitational-wave experiments have detected black holes of similar mass, but the formation of such massive ones in a high-metallicity environment would be extremely challenging within current stellar evolution theories. Radial-velocity measurements of a Galactic B-type star show a dark companion that seems to be a black hole of about 68 solar masses, in a widely spaced binary system.