Glossary term: Supergéante rouge

Description: Une supergéante rouge est une étoile dont la surface est relativement froide, mais dont le rayon est plusieurs centaines, voire plusieurs milliers de fois supérieur à celui d'une étoile de la séquence principale comme notre Soleil. La faible température donne à la surface un aspect rougeâtre, tandis que le grand diamètre rend l'étoile beaucoup plus brillante que notre Soleil.

Les supergéantes rouges se forment de la même manière que les géantes rouges, mais à partir d'étoiles beaucoup plus massives. Les deux types d'étoiles étaient à l'origine des étoiles de la séquence principale, c'est-à-dire des étoiles comme notre Soleil qui transforment l'hydrogène en hélium dans leur cœur par fusion nucléaire (bien que leur masse soit beaucoup plus élevée que celle du Soleil dans le cas des supergéantes rouges). Lorsqu'une telle étoile n'a plus d'hydrogène, elle commence à brûler de l'hélium en éléments plus lourds. À ce moment-là, l'étoile se dilate, sa surface se refroidissant au passage, et sa taille augmentant, elle devient plus lumineuse. La durée de vie des supergéantes rouges n'est que de quelques dizaines de milliers d'années.

Par exemple, Bételgeuse, dans Orion, ou Antarès, dans le Scorpion sont des supergéantes rouges. Comme les géantes rouges, elles sont sujettes à des pulsations et à une perte de masse. La plupart des supergéantes rouges, voire toutes, se terminent par l'explosion d'une supernova, éjectant une grande partie de leur gaz, leur cœur s'effondrant pour former des étoiles à neutrons ou des trous noirs.

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

Over a watery field, Orion is shaped like a bow-tie turned 45 degrees. The bright star Sirius is in the image's left half

Watchtower and Paddy Fields Under the Starry Sky

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.   This image, taken in April 2022, shows the sky over a plantation field around a century-old watchtower guarding a village in the province of Guangdong, China. Throughout the ages, the sky has been used as a tool for navigation and also as a calendar. By watching the apparent movement of the stars, it is possible to follow the passing of time, thereby understanding the change of the seasons which in turn helps to plan out the best timings of agricultural work. The most prominent constellations in this image are Orion and Canis Major, the Great Dog. Commonly associated with a giant hunter in Greek mythology, Orion is followed by his hound in the shape of the constellation Canis Major. In China, the seven bright stars of the constellation Orion are paradoxically called Three Stars (Shen) and this is one of the 28 Lunar Mansions. The Babylonian pre-zodiac, the so-called “Path of the Moon”, had 17 constellations and included Orion (therein named “True Shepherd of the Heavens”). This is not really surprising because, even in the system of the 88 modern constellations, the Moon sometimes stands in the constellation Orion. The modern constellation boundaries were defined in the 1920s in such a way that the area of Orion ends a half degree south of the ecliptic, in order to avoid the Sun entering it. Still, the Moon and the planets do occasionally. Therefore, Orion is part of the Zodiac (a stripe 5 to 10 degrees around the ecliptic), part of the path of the Moon and, of course, also used by many cultural calendars all over the world. Sirius, the bright star in the left half of the photograph, is the brightest star in the night sky, and has been used by many indigenous cultures to determine their calendars; the Egyptians awaited the Nile flood with Sirius’s heliacal rise, while the Romans connected its reappearance after its invisibility in daylight with the hottest summer time. In Old China, Sirius was considered a single-star asterism called The Wolf. The adjacent area was called The Market for Soldiers and the area in the southern part of Canis Major was imagined as the Bow with an Arrow. The reddish bright star in the top right corner is Betelgeuse, a red supergiant and one of the largest stars that can be seen with the naked eye. Orion’s Great Nebula below Orion’s Belt should be mentioned, but also the fainter huge red arc that is called Barnard’s Loop is clearly shown in this photograph. This galactic nebula and the circular red nebula around Orion’s not-so-bright head are both parts of star-forming regions, while the red nebula to the upper left of Orion is the Rosette Nebula in the unrecognisable constellation of Monoceros.
Credit: Likai Lin/IAU OAE

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

The bright stars in Orion trace a shape similar to a bow tie, here tilted by 45 degrees in-front is a ruined building

The Kingdom of Orion

Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns. This image, taken in January 2022, pictures a landscape from Navarra, a province in the north of Spain with ruins from old civilizations in the foreground. Above that, we see a partially cloudy and starry sky with the most prominent stars belonging to the star pattern Orion. Composed of many bright stars with several interesting deep sky objects within its boundaries, Orion is one of the 88 officially recognised IAU constellations. It originates from Greek mythology where the hero Orion is the son of the sea god Poseidon. Orion is characterised as a giant hunter lurking just before he attacks an animal (it is unclear which animal he attacks, but, in the original Babylonian version of the Gilgamesh saga, it is the Bull of Heaven depicted as the constellation Taurus). The modern planetarium interpretation depicts him as a Roman warrior raising up his shield, but the two accompanying dogs, represented by the constellations of Canis Major and Canis Minor, are reminiscent of the Greek hunter. Located at the celestial equator, the star pattern is visible all over the world and is interpreted differently in various mythologies, for example as three fishermen at a campfire in parts of Australia, as a butterfly in some parts of Africa, and as a stairway for the souls of ancestors in parts of South America. As Spain belonged to the Roman empire, the original constellations from earlier times are not known. There are some cave paintings on the Iberian peninsula that could possibly have astronomical references. However, there is uncertainty as to whether these painted figures on rocks depict star patterns. Orion is best visible from November to January. Its most recognisable feature is the “belt”, an asterism composed of three bright, aligned stars (Alnitak, Alnilam and Mintaka), also recognised by different cultures. Just below this belt is the Orion Nebula, a famous and widely studied star-forming region located about 1500 light-years from Earth. The constellation's brightest stars are Rigel — a blue supergiant which is one of the brightest stars in the sky — and Betelgeuse — a massive red supergiant. The former serves as the left foot, and the latter as the right shoulder of the hunter. While Rigel is in the middle of its life, Betelgeuse is expected to explode within the next few tens of thousands of years. The Orionids, a meteor shower with typical rates of dozens of meteors per hour, whose parent body is Halley’s Comet, can be seen every year in the area of Orion, next to the border with the constellation of Gemini during the month of October.
Credit: Carlos Zudaire/IAU OAE

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons