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Aging leads to a gradual decline in physical activity and disrupted energy homeostasis. The NAD + -dependent SIRT6 deacylase regulates aging and metabolism through mechanisms that largely remain unknown. Here, we show that SIRT6 overexpression leads to a reduction in frailty and lifespan extension in both male and female B6 mice. A combination of physiological assays, in vivo multi-omics analyses and 13 C lactate tracing identified an age-dependent decline in glucose homeostasis and hepatic glucose output in wild type mice. In contrast, aged SIRT6-transgenic mice preserve hepatic glucose output and glucose homeostasis through an improvement in the utilization of two major gluconeogenic precursors, lactate and glycerol. To mediate these changes, mechanistically, SIRT6 increases hepatic gluconeogenic gene expression, de novo NAD + synthesis, and systemically enhances glycerol release from adipose tissue. These findings show that SIRT6 optimizes energy homeostasis in old age to delay frailty and preserve healthy aging. Aging is associated with increased frailty and disrupted energy homeostasis. Here, the authors show that SIRT6 overexpression extends the lifespan of male and female mice and demonstrate that SIRT6 optimizes energy homeostasis in old age, which delays frailty and preserves healthy aging.

The final fate of massive stars, and the nature of the compact remnants they leave behind (black holes and neutron stars), are open questions in astrophysics. Many massive stars are stripped of their outer hydrogen envelopes as they evolve. Such Wolf–Rayet stars 1 emit strong and rapidly expanding winds with speeds greater than 1,000 kilometres per second. A fraction of this population is also helium-depleted, with spectra dominated by highly ionized emission lines of carbon and oxygen (types WC/WO). Evidence indicates that the most commonly observed supernova explosions that lack hydrogen and helium (types Ib/Ic) cannot result from massive WC/WO stars 2 , 3 , leading some to suggest that most such stars collapse directly into black holes without a visible supernova explosion 4 . Here we report observations of SN 2019hgp, beginning about a day after the explosion. Its short rise time and rapid decline place it among an emerging population of rapidly evolving transients 5 – 8 . Spectroscopy reveals a rich set of emission lines indicating that the explosion occurred within a nebula composed of carbon, oxygen and neon. Narrow absorption features show that this material is expanding at high velocities (greater than 1,500 kilometres per second), requiring a compact progenitor. Our observations are consistent with an explosion of a massive WC/WO star, and suggest that massive Wolf–Rayet stars may be the progenitors of some rapidly evolving transients. Observations of the supernova SN 2019hgp, identified about a day after its explosion, show that it occurred within a nebula of carbon, oxygen and neon, and was probably the explosion of a massive WC/WO star.

A mass-loss event 40 days before the explosion of the type IIn supernova SN 2010mc has been detected; the outburst indicates that there is a causal relation between explosive mass-loss events seen in some massive stars before their explosion and the onset of the supernova explosion. 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. Some observations suggest that very massive stars experience extreme mass-loss episodes shortly before they explode as supernovae 1 , 2 , 3 , 4 , as do several models 5 , 6 , 7 . Establishing a causal connection between these mass-loss episodes and the final explosion would provide a novel way to study pre-supernova massive-star evolution. Here we report observations of a mass-loss event detected 40 days before the explosion of the type IIn supernova SN 2010mc (also known as PTF 10tel). Our photometric and spectroscopic data suggest that this event is a result of an energetic outburst, radiating at least 6 × 10 47  erg of energy and releasing about 10 −2 solar masses of material at typical velocities of 2,000 km s −1 . The temporal proximity of the mass-loss outburst and the supernova explosion implies a causal connection between them. Moreover, we find that the outburst luminosity and velocity are consistent with the predictions of the wave-driven pulsation model 6 , and disfavour alternative suggestions 7 .

With the advent of new wide-field, high-cadence optical transient surveys, our understanding of the diversity of core-collapse supernovae has grown tremendously in the last decade. However, the pre-supernova evolution of massive stars, which sets the physical backdrop to these violent events, is theoretically not well understood and difficult to probe observationally. Here we report the discovery of the supernova iPTF 13dqy = SN 2013fs a mere ∼3 h after explosion. Our rapid follow-up observations, which include multiwavelength photometry and extremely early (beginning at ∼6 h post-explosion) spectra, map the distribution of material in the immediate environment (≲10 15  cm) of the exploding star and establish that it was surrounded by circumstellar material (CSM) that was ejected during the final ∼1 yr prior to explosion at a high rate, around 10 −3 solar masses per year. The complete disappearance of flash-ionized emission lines within the first several days requires that the dense CSM be confined to within ≲10 15  cm, consistent with radio non-detections at 70–100 days. The observations indicate that iPTF 13dqy was a regular type II supernova; thus, the finding that the probable red supergiant progenitor of this common explosion ejected material at a highly elevated rate just prior to its demise suggests that pre-supernova instabilities may be common among exploding massive stars. Type II supernova explosions are common, but our understanding of such events is not complete. Such an event was observed just three hours after the explosion started, providing important information about the early stages.

We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova, iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because the light from the stellar explosion was magnified more than 50 times by the curvature of space around matter in an intervening galaxy. We used high-spatial-resolution observations to resolve four images of the lensed supernova, approximately 0.3 arc seconds from the center of the foreground galaxy. The observations probe a physical scale of ~1 kiloparsec, smaller than is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration imply close alignment between the lines of sight to the supernova and to the lens. The relative magnifications of the four images provide evidence for substructures in the lensing galaxy.

The detection of strong emission lines in an early-time spectrum of type IIb supernova SN 2013cu reveals Wolf–Rayet-like wind signatures, suggesting that the supernova’s progenitor may have been a Wolf–Rayet star with a wind dominated by helium and nitrogen, with traces of hydrogen. Progression from Wolf-Rayet star to type IIb supernova Wolf–Rayet stars, massive objects stripped of their outer hydrogen-rich envelope, are one of a number of candidates as supernova progenitors for type IIb, Ib and Ic explosions. This paper reports the detection of strong emission lines in early spectra — just 15 hours after the blast — from the type IIb supernova SN 2013cu that are consistent with a Wolf–Rayet star as progenitor. The extent of this dense supernova wind implies possible increased mass loss from the progenitor shortly before the explosion, consistent with recent theoretical predictions. An accompanying News & Views article suggests that the new findings are the most direct evidence yet that these massive stars do end their lives as supernovae. The explosive fate of massive Wolf–Rayet stars 1 (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen-deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic (ref. 2 ). A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib (ref. 3 ), but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections 4 . Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 10 12  centimetres, as expected for some WRSs 5 . The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by ‘flash spectroscopy’, which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star). We identify Wolf–Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions 6 .

The early evolution of a supernova (SN) can reveal information about the environment and the progenitor star. When a star explodes in vacuum, the first photons to escape from its surface appear as a brief, hours-long shock-breakout flare 1 , 2 , followed by a cooling phase of emission. However, for stars exploding within a distribution of dense, optically thick circumstellar material (CSM), the first photons escape from the material beyond the stellar edge and the duration of the initial flare can extend to several days, during which the escaping emission indicates photospheric heating 3 . Early serendipitous observations 2 , 4 that lacked ultraviolet (UV) data were unable to determine whether the early emission is heating or cooling and hence the nature of the early explosion event. Here we report UV spectra of the nearby SN 2023ixf in the galaxy Messier 101 (M101). Using the UV data as well as a comprehensive set of further multiwavelength observations, we temporally resolve the emergence of the explosion shock from a thick medium heated by the SN emission. We derive a reliable bolometric light curve that indicates that the shock breaks out from a dense layer with a radius substantially larger than typical supergiants. Using ultraviolet data as well as a comprehensive set of further multiwavelength observations of the supernova 2023ixf, a reliable bolometric light curve is derived that indicates the heating nature of the early emission.

When a star passes within the tidal radius of a supermassive black hole, it will be torn apart 1 . For a star with the mass of the Sun ( M ⊙ ) and a non-spinning black hole with a mass <10 8 M ⊙ , the tidal radius lies outside the black hole event horizon 2 and the disruption results in a luminous flare 3–6 . Here we report observations over a period of ten months of a transient, hitherto interpreted 7 as a superluminous supernova 8 . Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution 6 , the presence of highly ionized CNO gas in the line of sight 9 and our improved localization of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely 10,11 . While the supermassive black hole has a mass >10 8 M ⊙ 12,13 , a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly 14 . The rapid spin and high black hole mass can explain the high luminosity of this event. Transient object ASASSN-15lh was previously cast as the most luminous supernova ever discovered. Now, however, there is convincing evidence that its flare was a tidal disruption event: a rapidly-spinning black hole tearing apart a neighbouring star.