The modestly sized Corona Borealis constellation can be recognized by the characteristic semi-circle shape from which it takes its name – think of the laurel wreath awarded to winners of the ancient Olympic Games. It is quite easily spotted in the sky, somewhere between the two bright stars Vega and Arcturus.
Let’s face it, the Corona Borealis is not the best known of asterisms. However, one of its stars will be the subject of the attention of many amateur and professional astronomers, because, in the coming weeks or months, it will be the scene of a spectacular explosion. Currently invisible to the naked eye, T Coronae Borealis (this is its scientific name, the abbreviation of which is T CrB) will, for a few days, suddenly shine in the firmament, as if a new star had been born – the phenomenon is d elsewhere designated by the Latin term “nova”. T CrB will perhaps shine as bright as the North Star. The best part of the story is that this spectacular apparition has already been observed several times in the past. Indeed, unlike certain stars which only give off a single firework, T of the Boreal Crown is a repeating rifle.
The secret of this Winchester lies in its composition: as Florentin Millour, astrophysicist at the Côte d’Azur Observatory, explains, “it is a pair of stars which orbit each other, but which are not at the same stage of their evolution. One is a white dwarf, a dead star with only its heart remaining. The other is a red giant – this is the stage of evolution just before death – and it still has some fuel left.”.
A gigantic ball of fire
The duo turns out to be close enough for the white dwarf to tear off some of its neighbor’s flesh. This material, essentially hydrogen, ends up being deposited on its surface. “It accumulates, and, after a certain time, the quantity of hydrogen is sufficient for a thermonuclear explosion to begin, ejecting into space a gigantic fireball which creates the nova”concludes Florentin Millour.
The explosion does not destroy either the white dwarf or its neighbor, and the process can start again, hence the name “recurrent nova” given to systems such as T CrB. The latter lights up every eight decades. Modern science has observed two of the novae it produced, in 1866 and 1946. In an article published in 2023, American astronomer Bradley Schaefer found and analyzed two other occurrences in ancient documents: one in 1787 in a star catalog and the other in 1217 in a medieval chronicle.
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