BOOM! A New Kind of Supernova Has Been Discovered

This artist’s impression exhibits the brilliant core of a Wolf–Rayet star surrounded by a nebula of fabric that has been expelled by the star itself. Credit score: ESO/L. Calçada

We regularly consider supernova explosions as inevitable for big stars. Massive star runs out of gasoline, gravity collapses its core, and BOOM! However astronomers have lengthy thought a minimum of one kind of huge star didn’t finish with a supernova. Often known as Wolf-Rayet stars, they had been thought to finish with a quiet collapse of their core right into a black gap. However a brand new discovery finds they may change into supernovae in any case.

Wolf-Rayet stars are among the many most large stars recognized. They're on the finish of their quick lives, however relatively than merely working out of gasoline and exploding, they push out their outer layers with an especially highly effective stellar wind. This produces a surrounding nebula wealthy in ionized helium, carbon, and nitrogen, however nearly no hydrogen. The floor temperature of the remaining star might be over 200,000 Ok, making them essentially the most luminous stars recognized. However as a result of most of that mild is within the ultraviolet vary, they don't seem to be significantly shiny to the bare eye.

Wolf-Rayet star. Credit score: Hubble Legacy Archive, NASA, ESA – Processing & Licence: Judy Schmidt

Even with the outer layers of a Wolf-Rayet star solid off, the central star remains to be rather more large than the Solar. So that you’d determine it’s solely a matter of time earlier than it turns into a supernova. Regardless of how far up the periodic desk fusion happens, it would ultimately run out of gasoline, resulting in a core-collapse supernova. However we will see the spectra of parts inside a supernova, and we’d by no means seen a spectrum that matched a Wolf-Rayet star. As our discovery of supernovae grew to become commonplace, some astronomers started to surprise if Wolf-Rayet stars had a quiet dying as a substitute. The concept was that they'd solid off sufficient outer layers that the remaining core would ultimately simply collapse straight right into a black gap. No large explosion wanted. A silent dying to an enormous star.

In a big star, totally different parts are in layers earlier than the star explodes. Credit score: Itai Raveh

This newest research exhibits that a minimum of some Wolf-Rayet stars do change into supernovae. The staff seemed on the spectrum of a supernova referred to as SN 2019hgp, which was found by the Zwicky Transient Facility (ZTF). The supernova’s spectrum had shiny emission mild indicating the presence of carbon, oxygen, and neon, however not hydrogen or helium. When the staff seemed on the information extra intently, they discovered these explicit emission traces weren’t attributable to parts of the supernova straight. As a substitute, they had been a part of a nebula increasing away from the star at greater than 1,500 km/s.

A spectra from SN 2019hgp. Credit score: Itai Raveh

In different phrases, earlier than the supernova occurred, the progenitor star was surrounded by a nebula wealthy in carbon, nitrogen, and neon, whereas missing the lighter parts of hydrogen and helium. The growth of the nebula will need to have been pushed by robust stellar winds. This matches the construction of a Wolf-Rayet star extraordinarily effectively. So it appears like SN 2019hgp is the primary instance of a Wolf-Rayet supernova. Since then, related supernovae have additionally been detected.

As a result of this supernova was recognized by spectra of the encircling nebula, it isn’t clear whether or not the explosion was a easy supernova, or whether or not it was a extra advanced hybrid course of the place the higher layer of the star exploded whereas the core collapsed on to a black gap. It would take extra observations to find out the small print. What’s clear is that a minimum of some Wolf-Rayet stars don't go silently into the evening.

Initially revealed on Universe At this time.

Reference: “A WC/WO star exploding inside an increasing carbon–oxygen–neon nebula” by A. Gal-Yam, R. Bruch, S. Schulze, Y. Yang, D. A. Perley, I. Irani, J. Sollerman, E. C. Kool, M. T. Soumagnac, O. Yaron, N. L. Strotjohann, E. Zimmerman, C. Barbarino, S. R. Kulkarni, M. M. Kasliwal, Ok. De, Y. Yao, C. Fremling, L. Yan, E. O. Ofek, C. Fransson, A. V. Filippenko, W. Zheng, T. G. Brink, C. M. Copperwheat, R. J. Foley, J. Brown, M. Siebert, G. Leloudas, A. L. Cabrera-Lavers, D. Garcia-Alvarez, A. Marante-Barreto, S. Frederick, T. Hung, J. C. Wheeler, J. Vinkó, B. P. Thomas, M. J. Graham, D. A. Duev, A. J. Drake, R. Dekany, E. C. Bellm, B. Rusholme, D. L. Shupe, I. Andreoni, Y. Sharma, R. Riddle, J. van Roestel and N. Knezevic, 12 January 2022, Nature.
DOI: 10.1038/s41586-021-04155-1