Free Astronomy Magazine March-April 2022

35 MARCH-APRIL 2022 ASTRO PUBLISHING The life spans of massive stars are considered relatively short, a few million years at most. The Sun, in comparison, has a life expectancy of about 10 billion years. The subse- quent processes of nuclear fusion at the core of massive stars lead to their stratification, in which the heavy elements are concentrated at the core, and gradually lighter ele- ments compose the outer layers. Wolf-Rayet stars are particularly massive stars that are missing one or more of the external layers that are made up of lighter elements. In this way, instead of hydrogen – the lightest element – the star’s surface is characterized by the presence of helium, or even carbon and heavier elements. One possible explanation for this phenomenon is that strong winds blowing due to high pressure at the star’s envelope, disperse its outermost layer, thus causing the star to lose one layer after the other over several hundred thousand years. Despite their relatively short life spans and their state of progressive disintegration, analysis of the ever- growing number of supernova dis- coveries has led to the hypothesis that Wolf-Rayet stars simply don’t explode – they just quietly collapse into black holes – otherwise, we would have been able to observe one by now. This hypothesis, how- ever, has just been shattered owing to the recent discovery. Spectroscopic analysis of the light emitted from the explosion led to the discovery of spectral signatures that are associated with specific el- ements. In this way, the researchers were able to show that the explo- sion contained carbon, oxygen and neon atoms, the latter an element that has not yet been observed in this manner in any supernova to date. Moreover, the researchers identified that the matter spouting cosmic radiation did not in itself participate in the blast but rather originated from the space surround- ing the volatile star. This, in turn, strengthened their hypothesis in favor of strong winds that took part in stripping the star of its outer en- velope. Since this observation is the first of its kind, Gal-Yam states that it may be too early to unequivocally deter- mine the fate of all such stars. “We can’t say at this stage whether all Wolf-Rayet stars end their lives with a bang or not. It might be that some of them do collapse quietly into a black hole,” he says. Researchers estimate that the mass that dispersed during the explosion is probably equal to that of the Sun or a slightly smaller star; the star that exploded was significantly heavier – having a mass at least ten times greater than that of the Sun, so scientists wonder where the ma- jority of mass end up. Gal-Yam suggests a midway sce- nario, in which both possible fates are fulfilled at the same time: once nuclear fusion is exhausted at the star’s core, an explosion takes place that blasts some of the mass into space, while the remaining mass col- lapses in on itself, forming a black hole. “One thing’s certain,” says Gal-Yam, “This is not the ‘silent’ col- lapse often referred to in the past.” The study has used observations made with different telescopes, in- cluding the Gran Telescopio Ca- narias (GTC or Grantecan) located at the Roque de los Muchachos Obser- vatory (Garafía, La Palma). For Antonio Cabrera Lavers, head of scientific operations at Grantecan and affiliated researcher at the IAC who participated in the study, “It is worth mentioning that since this discovery was first made, another similar explosion of a Wolf-Rayet star has been observed, implying that this phenomenon is indeed not a single occurrence.” A Wolf-Rayet star and the nebula surrounding it captured by the Hubble Space Telescope. Gal-Yam and colleagues are the first to discover a rare-type su- pernova originating from this star. [NASA/ESA Hubble Space Telescope] !