Minutes-duration optical flares with supernova luminosities

In recent years, certain luminous extragalactic optical transients have been observed to last only a few days1. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks2. Some short-duration transients, most notably AT2018cow (ref. 3), show blue optical colours and bright radio and X-ray emission4. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source5, such as X-ray variability6,7, prolonged ultraviolet emission8, a tentative X-ray quasiperiodic oscillation9,10 and large energies coupled to fast (but subrelativistic) radio-emitting ejecta11,12. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the ‘Tasmanian Devil’). The flares occur over a period of months, are highly energetic and are probably nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that, in some AT2018cow-like transients, the embedded energy source is a compact object, either a magnetar or an accreting black hole

Intraspecific variation in testis asymmetry in birds: evidence for naturally occurring compensation

In many taxa, the left and right testes often differ in size. The compensation hypothesis states that one testis of the pair serves as a ‘back-up’ for any reduced function in the other and provides a mechanism to explain intraspecific variation in degree and direction of gonad asymmetry. Although testis asymmetry is common in birds, evidence for natural testis compensation is unknown. Using a novel quantitative approach that can be applied to any bilateral organ or structure, we show that testis compensation occurs naturally in birds and can be complete when one testis fails to develop. Owing to a recurrent risk of testis impairment and an evolutionary trade-off between natural and sexual selections acting on the arrangement of internal organs in species with abdominal and/or seasonal testes, compensation adds an important, but neglected, dimension to measures of male reproductive investment