Hypergiant
A hypergiant ( luminosity class 0) is a star with enormous mass and luminosity .
properties
Hypergiants have a volume similar to supergiants , but are even more massive and are characterized by a very high luminosity. Some hypergiants have more than 100 solar masses, although at the beginning of their development they could have been as high as 200 to 250 solar masses. This brings them up to the Eddington limit , a theoretical maximum limit for star mass, above which a star generates so much radiation that its outer layers are no longer attracted by gravity, but repelled. The exact mechanisms of the formation and development of such massive stars as well as the numerical value of the Eddington limit are the subject of current research.
With a thousand to million times the luminosity of the sun, hypergiants are the brightest stars in the universe. However, their surface temperatures are very different. They range from 3,500 K to over 35,000 K. Almost all hypergiants show variations in their luminosity. The reasons lie in instabilities inside them at moderate temperatures and high pressures.
Due to the large internal energy turnover, the lifespan of the hypergiant is only a few million years. Then they explode as a supernova or as a (hypothetical) hypernova . It is believed that a hypergiant left behind a stellar black hole . However, it could also be completely destroyed by a special form of supernova, the pair instability supernova .
Well-known hypergiants
Hypergiants are difficult to observe and study due to their rarity. There seems to be an upper limit to their luminosity for the cooler, yellow or red glowing hypergiants. None of them is brighter than about −9.5 m absolute brightness . This corresponds to about 500,000 times the light intensity of the sun. The reasons for this are still unknown.
Luminous Blue Variables (LBV)
The most massive specimens of the bright blue variables belong to the group of hypergiants and to the brightest known stars:
- Deneb , the brightest star from Earth in the constellation of the Swan , which together with Altair and Vega , the Summer Triangle is. He is the most famous LBV.
- P Cygni also in the constellation of the swan, whose extremely fluctuating absolute brightness currently even exceedsthat of Deneb.
- S Doradus in the nearby galaxy Large Magellanic Cloud . This is located in the southern constellation Swordfish . The 1987A supernova also took place in this galaxy.
- Eta Carinae within the Carina Nebula ( NGC 3372 ). This star is located in the southern constellation Kiel of the ship . Eta Carinae is extremely massive, possibly up to 120 or 150 times the mass of the Sun and 4 or 5 million times brighter than the Sun.
- The pistol star in the quintuplet star cluster near the center of our galaxy in the constellation Sagittarius . It is possible that this star has 150 times the mass of the Sun and is 1.7 million times brighter than the Sun.
- Several stars in the star cluster 1806–20 . These are located on the opposite side of our galaxy from our solar system. One of these stars, LBV 1806-20 , is the brightest star known to date, about 2 to 40 million times as bright as the Sun. At the same time, it is one of the most massive stars anywhere.
Blue hypergiant
- Zeta-1 Scorpii, the brightest star of the OB agglomeration Scorpius OB1 and an LBV candidate.
- MWC 314 in the constellation Adler , another LBV star.
- HD 169454 in the constellation Shield .
- BD −14 ° 5037 near Cygnus OB2.
- Cygnus OB2 # 12 , which some authors consider LBV.
- QPM-241 in the quintuplet star cluster in the constellation Sagittarius
Yellow hypergiant
Yellow hypergiants are an extremely rare class of stars. There are likely very few large stars that do not have the required mass to become LBV. Shortly before they end, they transform into hypergiants with a yellow or white phase. Only seven specimens are known in our galaxy:
- Rho Cassiopeiae (7 Cas) in the northern constellation Cassiopeia is about 550,000 times brighter than the Sun and 10,000 light years away from us. Because of its current pulsations, it is a candidate for the next supernova in our galaxy.
- V509 Cassiopeiae (HR 8752)
- V382 Carinae (x Carinae)
- IRC + 10420 , in the constellation Eagle
- HR 5171 A, in the constellation Centaur
- some stars in the star cluster Westerlund 1
Red hypergiant
Specialty
One of the most massive stars known is R136a1 in the Tarantula Nebula of the Large Magellanic Cloud. It is around a million years old, has 265 times the mass of our sun (from previously around 320 solar masses ) and is ten million times brighter than our sun . Until now it was assumed that there were no stable stars beyond 150 solar masses. R136a1 is part of a whole cluster of young, massive giant stars; the star density there is 100,000 times higher than that in the vicinity of our sun.
See also
Notes and individual references
- ↑ a b Brightest giant star discovered. In: derStandard.at. Retrieved June 7, 2019 (Austrian German).
- ↑ About Stars: Intermediate Levels - Page in the Astronomy: Stars & Planets section at Jumk.de , accessed on March 18, 2014
- ↑ The Yellow Hyper Giant ( Memento from January 3, 2008 in the Internet Archive ) - from Welt der Naturwissenschaften , in 2003, accessed on March 18, 2014
- ↑ Star with 1,300 times the diameter of the sun - report at Science.ORF.at , from March 12, 2014. Accessed on March 16, 2014
- ↑ Rare giant star measured - a million times brighter than the sun ( Memento from March 13, 2014 in the Internet Archive ) - report at Tagesschau.de , March 12, 2014. Accessed on March 16, 2014
- ↑ Earth and Universe - Astronomy: Cosmic Giant - Message from Bild der Wissenschaft , from March 12, 2014. Accessed on March 18, 2014
- ↑ Hypergiant: ESO discovers gigantic yellow star - Reported by Heise online , March 13, 2014. Accessed March 16, 2014