On the outskirts of the Milky Way, there is a mysterious star. A star that surprised astronomers with its original composition. According to them, it can only be explained by the past explosion of a massive star in hypernova. An extremely violent phenomenon that played out in the childhood of the Universe. And who could help to understand how the heavy elements formed.
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[EN VIDÉO] Two neutron stars merge into a black hole In this animation (not an observation), NASA shows what is believed to be the collision of two neutron stars that formed a pair, one rotating around the other. Resulting from the collapse of a large star, these stars are extremely dense. When the two bodies get too close, the tidal forces begin to tear them apart. Red areas show regions of lower density. Fusion gives a body so dense that it becomes a black hole. This scenario was validated in October 2017 by the analysis of gravitational waves spotted by Ligo and Virgo in August 2017 from the source called GW170817. © NASA
It is called SMSS J200322.54-114203.3. Not easy to remember. Yet this star stands out. It is located at some 7,500 light years of our Sun, in the periphery of the Milky Way. It presents a composition of the strangest. Low in do, but high amounts ofazote, from zinc, d’uranium, d’europium and maybe even gold. In other words, more heavy elements than it should have.
To explain this composition, Australian National University astronomers (Astro 3D) argue today that there is only one possibility. SMSS J200322.54-114203.3 must have arisen from the ashes of an explosion predicted by theory, but never observed before: the explosion of a star in hypernova magnetorotational. Kind of like a explosion en supernova, but amplified by the rapid rotation of the star in the presence of magnetic fields intense.
Remember that in order to form heavier elements that iron, theUniverse must rely on intense forces. Of type fusion of neutron stars or explosion of massive stars in supernova. Heavy elements are in fact formed when lighter elements absorb many neutrons. Some disintegrate into protons and eventually land on a stable isotope of a heavy element. These elements are then dispersed in the interstellar medium by the force of the explosion or the collision. They end up in other stars or on planets like Earth.
A hypernova: the only possible explanation
First important observation regarding SMSS J200322.54-114203.3: it has an extremely low iron content compared to its iron content. hydrogen. Almost 3,000 times smaller than that of our Sun. As iron is produced by melting carbone in massive stars and then scattered to their death, only a star formed in the youth of a galaxy may also contain little iron. What makes say astronomers that the mysterious star must have formed while the Milky Way was still very young. Some 13 billion years ago. In the very childhood of our Universe.
Thus SMSS J200322.54-114203.3 appeared too early in the history of the Universe for a neutron star collision was able to produce all the elements measured by the researchers. And its high zinc abundance directs them towards a very energetic explosion. “It is even a sure marker of a hypernova explosion”, underlines Brian Schmidt, cosmologist co-author of the study and Nobel Prize for physics in 2011. An explosion about 10 times more energetic than an ordinary supernova.
The nitrogen concentration seems to confirm that the source star – a star probably 25 times more massive than the Sun and highly magnetized – of SMSS J200322.54-114203.3 must have been rotating very fast. This is indeed how the hydrogen and carbon of a star can come together to form the much rarer element.
Have astronomers also found traces of the black hole who must have resulted from this massive explosion? No. But the composition of SMSS J200322.54-114203.3 does not seem explainable other than by a hypernova explosion. And they explain that if other stars of the same type may have appeared in the Universe, they have probably already died out. Or found diluted in more ordinary supernova remains.