Scientists from Russia, the United State and Germany told the world in their paper in Nature that supernovas can explode several times.

When “life” of a supernova comes to an end, the star collapses and explodes, illuminating its surroundings. This event is a rare bird, but observing several consecutive “deaths” of a star happens once in a lifetime. This is what a SN 2006gy supernova had to get through. This star exploded in a galaxy named NGC 1260, which is 240 million light years far from our planet. Observations of the last years revealed a supernova, which was a hundred times more bright that usual supernova and led scientists to think about reasons for such an event.

Stan Woosley from California University of Santa Cruz, Sergey Blinnikov from Russian Institute of Theoretical and Experimental Physics and German researcher Alexander Heger, currently employed in Los Alamos National Laboratory suggest a theory, explaining abovementioned phenomenon. The scientists have developed a model, which agrees with observation data of the supernova.

According to Mr. Woosley this supernova was extremely bright, and researchers claim their model is the best way to describe new mechanisms of supernova outbursts, which repeat in the same star. We got used to an opinion that supernova outburst is star’s death, however, sometimes one star explodes half a dozen times. A supernova usually explodes when a massive star “consumes” all fuel resources and collapses. In this particular case the supernova explodes several times. First explosion is not very powerful and throws out star’s outer shell – upper layers. Second explosion that may happen several years later, casts off star’s second cover, which rapidly extends and collides with the first one, causing bright outburst. “Two shells collide at such a distance, which transforms all kinetic energy to light, making the explosion a hundred times brighter than ordinary supernova does”, the scientists explain. Usually supernova allows only one per cent of its kinetic energy to become light.

Such a scenario requires an extremely massive star – weighing from 90 to 130 Suns. When such a massive star comes to an end of its life cycle, temperature in its core reaches extremely high values, causing part of gamma radiation turning into electron and positron pairs. These transformations result in “pair instability” effect, when radiation turning into electron-positron pairs causes abrupt drop in pressure, and the start starts shrinking quickly.

Since the star core shrinks, it becomes more and more unstable, until it collapses and explodes. Then the star expands again, but not enough for it to be totally destroyed. During the next stage the star expands, emits energy again and shrinks, and then it heats one more time and everything repeats once again”, comment the scientists. Processes of expanding and shrinking continue, until the star loses enough weight to become stable again.

Such massive stars occur quite rarely, especially in our galaxy, however, they could have been frequent guests during “childhood” of the Universe.

Source:
    Science News

Kizilova Anna