Scientists at the Weizmann Institute have identified a new type of supernova in a galaxy a billion light-years away
In the not-too-distant past, locating a supernova – an exploding star – was considered a rare sight. When Prof. Avishai Gal-Yam, for example, studied for a doctorate, he found seven supernovae in four years. Today, improvements in the means of measurement and analysis make it possible to predict about fifty such explosions every day. Astrophysicists’ improved ability to predict supernovae may make the celestial event less exciting, but the increase in frequency raises the likelihood of predicting rarer types of explosions – hitherto considered purely theoretical. Prof. Gal-Yam and his research partners have recently identified a supernova of a type not previously observed. Their findings are published today in the scientific journal Nature.
At the core of every star, at any given moment, a process of nuclear fusion takes place: light elements merge and become, little by little, heavier elements. The fusion of hydrogen nuclei turns into helium, which turns into carbon and oxygen, and so on. At the end of the process, iron is formed – from which nuclear energy cannot be extracted. Under normal circumstances, the energy generated in the star’s core creates heat that seeks to cause the star to propagate, allowing it to maintain balance with gravity – which pushes the star’s mass into the core. As soon as a star stops producing energy – the balance is disturbed, and can lead to one of two results: either a black hole opens in the star’s core – causing it to collapse into itself, or it explodes – and disperses the matter from which it is made into space.
This is, of course, a very long process. The lifespan of massive stars, which is being researched by Prof. Gal-Yam – Dean of the Faculty of Physics at the Weizmann Institute of Science – is considered relatively short: a few million years at most. The sun, by comparison, is expected to live about 10 billion years. In massive stars, nuclear fusion in the core creates a situation where the star is composed of layers – the heavy elements are at its core, and lighter and lighter elements surround them. Wolf-vision stars are extremely massive stars that lack one or more of the upper layers of the light elements, so that instead of hydrogen – the lightest element – the surface will be characterized by helium, carbon or even a heavier element. A possible explanation for this phenomenon is that a strong wind blowing from the star’s shell out disperses into space the outermost layer, and so these stars lose another layer every few hundred thousand years. When stars without light elements are observed in their outer layer – this is a still image that documents a moment in a long process. But despite their relatively short lifespan, and the very fact that they are in the process of advanced decomposition, so far no supernova originating from the planet Wolf-Vision has been observed.
Analysis of the spectral signature of the radiation emitted from the star’s explosion revealed the presence of a neon – an element not previously observed in any supernova
The rapid growth rate of supernova observations has reinforced the hypothesis that for unknown reasons, wolf-sighted stars do not explode – for, if they had exploded, we would have already predicted such an explosion. But recently, members of Prof. Gal-Yam’s research group have been able to refute the hypothesis and identify, for the first time, a supernova that originated in this type of star. Analysis of the spectral signature of the explosion – from which one can learn about the wavelengths of light emission, and belong to one element or another – showed that the explosion contained carbon, oxygen and neon – an element not previously observed in any supernova. Beyond that, the scientists recognized that the material from which the cosmic radiation was emitted did not itself participate in the explosion, but came from the star’s shell – something that strengthens the strong spirit belief.
“Because this is a first observation, Prof. Gal-Yam says it is too early to state unequivocally that this is the end of every star:” We do not know at this point whether all Wolf-vision stars are exploding. Some may be collapsing into a black hole, “he says. “We estimate that the mass dissipated from the explosion was similar to or smaller than the mass of the sun, while the star was originally much more massive – at least 10 times the mass of the sun. So where did most of the mass go?” To explain this he proposes an intermediate scenario, in which the two possibilities exist, simultaneously: after nuclear energy ceases to form in the star core, an explosion takes place that throws some of the mass into space, and at the same time the rest of the mass collapses into the star core. “What is certain,” says Prof. Gal-Yam, “is not the quiet collapse they were talking about. It is worth noting that since this first discovery, another explosion of a Wolf-Star has been observed – that is, it is not a one-time event. The measurement and detection, to predict such explosions – which are now considered exotic and rare – will become a matter of routine. “
Supernova explosions can be perceived as distant and vast events, which have no direct impact on our lives, but the truth is that they are at the base of life itself. The explosions allow elements formed in the core of the star to disperse throughout the galaxy, forming new stars. The earth and everything in it – including us – were also created as a result of this process. “We are researching the source of substances in nature, and are looking for explanations for the phenomena we take for granted,” concludes Prof. Gal-Yam. “That’s what interests me – where did everything around us come from – and I want to understand this process as best I can.”
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