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Superluminous supernovae radiate up to 100 times more energy than normal supernovae. The origin of this energy and the nature of the stellar progenitors of these transients are poorly understood. We identify neutral iron lines in the spectrum of one such supernova, SN 2006gy, and show that they require a large mass of iron (≳0.3 solar masses) expanding at 1500 kilometers per second. By modeling a standard type Ia supernova hitting a shell of circumstellar material, we produce a light curve and late-time iron-dominated spectrum that match the observations of SN 2006gy. In such a scenario, common envelope evolution of a progenitor binary system can synchronize envelope ejection and supernova explosion and may explain these bright transients.

To be observed and analyzed by the network of current gravitational-wave detectors (LIGO, Virgo, KAGRA), and in anticipation of future third generation ground-based (Einstein Telescope, Cosmic Explorer) and space-borne (LISA) detectors, inspiralling compact binaries—binary star systems composed of neutron stars and/or black holes in their late stage of evolution prior the final coalescence—require high-accuracy predictions from general relativity. The orbital dynamics and emitted gravitational waves of these very relativistic systems can be accurately modelled using state-of-the-art post-Newtonian theory. In this article we review the multipolar-post-Minkowskian approximation scheme, merged to the standard post-Newtonian expansion into a single formalism valid for general isolated matter system. This cocktail of approximation methods (called MPM-PN) has been successfully applied to compact binary systems, producing equations of motion up to the fourth-post-Newtonian (4PN) level, and gravitational waveform and flux to 4.5PN order beyond the Einstein quadrupole formula. We describe the dimensional regularization at work in such high post-Newtonian calculations, for curing both ultra-violet and infra-red divergences. Several landmark results are detailed: the definition of multipole moments, the gravitational radiation reaction, the conservative dynamics of circular orbits, the first law of compact binary mechanics, and the non-linear effects in the gravitational-wave propagation (tails, iterated tails and non-linear memory). We also discuss the case of compact binaries moving on eccentric orbits, and the effects of spins (both spin-orbit and spin–spin) on the equations of motion and gravitational-wave energy flux and waveform.

In this context, the recent report1 of an approximately 70-solar-mass (M®) black hole in the galactic binary system LB-1 challenges conventional theories of massive-star evolution, stellar winds and core-collapse supernovae, thus requiring a more exotic scenario to explain the existence and properties of this system2,3. [...]we used a barycentre method as well as a bisector method using an identical mask as that in Liu et al.1, to estimate the apparent radial-velocity shift resulting from the combined Ha profile, obtaining similar results using both methods. [...]there is no evidence for a large mass ratio, and hence also no evidence for a large absolute mass of a black hole. Data availability The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request. https://doi.org/10.1038/s41586-020-2216-x Received: 6 December 2019 Accepted: 27 February 2020 Published online: 29 April 2020 Acknowledgements We acknowledge support from the Fonds Wetenschappelijk Onderzoek (FWO, Research Foundation Flanders) under project IDs G0F8H6N, G0B3818N, 12ZY520N, G0H5416N and GST-D6267-I002519N, and from the Onderzoeksraad (Research Council), KU Leuven under project IDs C16/17/007, C16/18/005 and C14/17/082.

Some types of core-collapse supernovae are known to produce a neutron star (NS). A binary NS merger was recently detected from its gravitational wave emission, but it is unclear how such a tight binary system can be formed. De et al. discovered a core-collapse supernova with unusual properties, including the removal of the outer layers of the star before the explosion. They interpret this as the second supernova in an interacting binary system that already contains one NS. Because the explosion probably produced a second NS (rather than a black hole) in a tight orbit, it could be an example of how binary NS systems form. Science , this issue p. 201 An unusual core-collapse supernova appears to have formed a binary neutron star in a tight orbit. Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (≈0.2 solar masses) and low kinetic energy (≈2 × 10 50 ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

Radio pulsars in short-period eccentric binary orbits can be used to study both gravitational dynamics and binary evolution. The binary system containing PSR J1141–6545 includes a massive white dwarf (WD) companion that formed before the gravitationally bound young radio pulsar. We observed a temporal evolution of the orbital inclination of this pulsar that we infer is caused by a combination of a Newtonian quadrupole moment and Lense–Thirring (LT) precession of the orbit resulting from rapid rotation of the WD. LT precession, an effect of relativistic frame dragging, is a prediction of general relativity. This detection is consistent with an evolutionary scenario in which the WD accreted matter from the pulsar progenitor, spinning up the WD to a period of <200 seconds.

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Mergings of compact-star binaries are expected to be the most important sources for forthcoming gravitational-wave (GW) astronomy. In the first part of the review, we discuss observational manifestations of close binaries with NS and/or BH components and their merger rate, crucial points in the formation and evolution of compact stars in binary systems, including the treatment of the natal kicks, which NSs and BHs acquire during the core collapse of massive stars and the common envelope phase of binary evolution, which are most relevant to the merging rates of NS-NS, NS-BH and BH-BH binaries. The second part of the review is devoted mainly to the formation and evolution of binary WDs and their observational manifestations, including their role as progenitors of cosmologically-important thermonuclear SN Ia. We also consider AM CVn-stars, which are thought to be the best verification binary GW sources for future low-frequency GW space interferometers.

A black hole X-ray binary produces hard X-ray radiation from its corona and disk when the accreting matter heats up. During an outburst, the disk and corona co-evolves with each other. However, such an evolution is still unclear in both its geometry and dynamics. Here we report the unusual decrease of the reflection fraction in MAXI J1820+070, which is the ratio of the coronal intensity illuminating the disk to the coronal intensity reaching the observer, as the corona is observed to contrast during the decay phase. We postulate a jet-like corona model, in which the corona can be understood as a standing shock where the material flowing through. In this dynamical scenario, the decrease of the reflection fraction is a signature of the corona’s bulk velocity. Our findings suggest that as the corona is observed to get closer to the black hole, the coronal material might be outflowing faster. Evolution of accretion disk and corona during outbursts in black hole binary systems is still unclear. Here, the authors show spectral analysis of MAXI J1820+070 and propose a scenario of a dynamical corona to explain the evolution of the reflection fraction observed by Insight-HXMT.

Common-envelope events (CEEs), during which two stars temporarily orbit within a shared envelope, are believed to be vital for the formation of a wide range of close binaries. For decades, the only evidence that CEEs actually occur has been indirect, based on the existence of systems that could not be otherwise explained. Here we propose a direct observational signature of CEEs arising from a physical model where emission from matter ejected in a CEE is controlled by a recombination front as the matter cools. The natural range of time scales and energies from this model, as well as the expected colors, light-curve shapes, ejection velocities, and event rate, match those of a recently recognized class of red transient outbursts.

Stellar mergers are a brief but common phase in the evolution of binary star systems 1 , 2 . These events have many astrophysical implications; for example, they may lead to the creation of atypical stars (such as magnetic stars 3 , blue stragglers 4 and rapid rotators 5 ), they play an important part in our interpretation of stellar populations 6 and they represent formation channels of compact-object mergers 7 . Although a handful of stellar mergers have been observed directly 8 , 9 , the central remnants of these events were shrouded by an opaque shell of dust and molecules 10 , making it impossible to observe their final state (for example, as a single merged star or a tighter, surviving binary 11 ). Here we report observations of an unusual, ring-shaped ultraviolet (‘blue’) nebula and the star at its centre, TYC 2597-735-1. The nebula has two opposing fronts, suggesting a bipolar outflow of material from TYC 2597-735-1. The spectrum of TYC 2597-735-1 and its proximity to the Galactic plane suggest that it is an old star, yet it has abnormally low surface gravity and a detectable long-term luminosity decay, which is uncharacteristic for its evolutionary stage. TYC 2597-735-1 also exhibits Hα emission, radial-velocity variations, enhanced ultraviolet radiation and excess infrared emission—signatures of dusty circumstellar disks 12 , stellar activity 13 and accretion 14 . Combined with stellar evolution models, the observations suggest that TYC 2597-735-1 merged with a lower-mass companion several thousand years ago. TYC 2597-735-1 provides a look at an unobstructed stellar merger at an evolutionary stage between its dynamic onset and the theorized final equilibrium state, enabling the direct study of the merging process. Observations and stellar evolution models of a blue ring nebula and its central star (TYC 2597-735-1) suggest that the remnant star merged with a lower-mass companion several thousand years ago.

Images collected during NASA’s Double Asteroid Redirection Test (DART) mission provide the first resolved views of the Didymos binary asteroid system. These images reveal that the primary asteroid, Didymos, is flattened and has plausible undulations along its equatorial perimeter. At high elevations, its surface is rough and contains large boulders and craters; at low elevations its surface is smooth and possesses fewer large boulders and craters. Didymos’ moon, Dimorphos, possesses an intimate mixture of boulders, several asteroid-wide lineaments, and a handful of craters. The surfaces of both asteroids include boulders that are large relative to their host body, suggesting that both asteroids are rubble piles. Based on these observations, our models indicate that Didymos has a surface cohesion ≤ 1 Pa and an interior cohesion of ∼10 Pa, while Dimorphos has a surface cohesion of <0.9 Pa. Crater size-frequency analyzes indicate the surface age of Didymos is 40–130 times older than Dimorphos, with likely absolute ages of ~ 12.5 Myr and <0.3 Myr, respectively. Solar radiation could have increased Didymos’ spin rate leading to internal deformation and surface mass shedding, which likely created Dimorphos. Images collected during NASA’s DART mission of the asteroid Didymos and its moon, Dimorphos, are used to explore the origin and evolution of the binary system. Authors analysis indicate that both asteroids are weak rubble piles and that Didymos’ surface should be about 40 to 130 times older than Dimorphos.