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Il est possible de prédire la vie d’une étoile à partir de sa taille. Ainsi, 3 grandes catégories ont été identifiées :
1- les étoiles les plus petites vont se consumer régulièrement jusqu’à s’éteindre en s’effondrant
2- Notre Soleil est une étoile de taille moyenne, juste au milieu de sa vie. Il va continuer à se dilater pour devenir une géante rouge, puis s’effondrer pour finir en naine blanche ; ce sera un astre gros comme la terre mais avec la masse du soleil, mais sans activité.
3- les plus grosses étoiles sont plus impressionnantes ; elles finiront en supernova, puis pourront évoluer en étoile à neutrons ou en trou noir

Ce n’est pas parce qu’une étoile est grosse qu’elle vivra plus longtemps, tout au contraire.

L’étoile se meurt. Elle a déjà fabriqué beaucoup d’éléments, et elle finira en apothéose.
L’énergie libéré lors de l’explosion d’une supernovæ est immense.
L’énergie de fusion de l’hydrogène n’est plus là pour inverser le sens de la force gravitationnelle, puisque le réservoir est épuisé.
La force gravitationnelle est à l’origine de l’explosion finale. C’est là que les autres éléments que nous connaissons sont synthétisés par fusion nucléaire.

Ça y est! Nous voyons enfin tous les éléments qui nous sont familiers sur notre Terre!

Si la masse de l’étoile est trop importante, alors il n’y aura pas de supernova … mais un trou noir…
Nous sommes des poussières d’étoiles
Parce ce que la matière qui forme notre chaire a été formée par l’étoile qui a donné naissance à notre système solaire

Mais nous avons aussi besoin de la poussière de supernova pour donner la diversité des atomes formant notre Terre !
Nous sommes des poussières de supernovæ.

Une étoile, ça peut mourir ?

Et oui, les étoiles naissent, grandissent, puis meurent

Continuons notre route avec Henry pour comprendre la vie des étoiles

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This image tracks the life of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant star on the right. On the left the star is seen as a protostar, embedded within a dusty disc of material as it forms. It later becomes a star like our Sun. After spending the majority of its life in this stage, the star’s core begins to gradually heat up, the star expands and becomes redder until it transforms into a red giant. Following this stage, the star will push its outer layers into the surrounding space to form an object known as a planetary nebula, while the core of the star itself will cool into a small, dense remnant called a white dwarf star. Marked on the lower timeline are where our Sun and solar twins 18 Sco and HIP 102152 are in this life cycle. The Sun is 4.6 billion years old and 18 Sco is 2.9 billion years old, while the oldest solar twin is some 8.2 billion years old —  the oldest solar twin ever identified. By studying HIP 102152, we can get a glimpse of what the future holds for our Sun. This image is illustrative; the ages, sizes, and colours are approximate (not to scale). The protostar stage, on the far left of this image, can be some 2000 times larger than our Sun. The red giant stage, on the far right of this image, can be some 100 times larger than the Sun.
A dying star’s final moments are captured in this image from the NASA/ESA Hubble Space Telescope. The death throes of this star may only last mere moments on a cosmological timescale, but this star’s demise is still quite lengthy by our standards, lasting tens of thousands of years! The star’s agony has culminated in a wonderful planetary nebula known as NGC 6565, a cloud of gas that was ejected from the star after strong stellar winds pushed the star’s outer layers away into space. Once enough material was ejected, the star’s luminous core was exposed and it began to produce ultraviolet radiation, exciting the surrounding gas to varying degrees and causing it to radiate in an attractive array of colours. These same colours can be seen in the famous and impressive Ring Nebula (heic1310), a prominent example of a nebula like this one. Planetary nebulae are illuminated for around 10 000 years before the central star begins to cool and shrink to become a white dwarf. When this happens, the star’s light drastically diminishes and ceases to excite the surrounding gas, so the nebula fades from view. A version of this image was entered into the Hubble’s Hidden Treasures basic image competition by contestant Matej Novak.
The Calabash Nebula, pictured here — which has the technical name OH 231.8+04.2 — is a spectacular example of the death of a low-mass star like the Sun. This image taken by the NASA/ESA Hubble Space Telescope shows the star going through a rapid transformation from a red giant to a planetary nebula, during which it blows its outer layers of gas and dust out into the surrounding space. The recently ejected material is spat out in opposite directions with immense speed — the gas shown in yellow is moving close to a million kilometres an hour. Astronomers rarely capture a star in this phase of its evolution because it occurs within the blink of an eye — in astronomical terms. Over the next thousand years the nebula is expected to evolve into a fully fledged planetary nebula. The nebula is also known as the Rotten Egg Nebula because it contains a lot of sulphur, an element that, when combined with other elements, smells like a rotten egg — but luckily, it resides over 5000 light-years away in the constellation of Puppis (The Poop deck).