Luminous blue variable
Encyclopedia
Hypergiant
A hypergiant is a star with a tremendous mass and luminosity, showing signs of a very high rate of mass loss.-Characteristics:...
variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s named after S Doradus
S Doradus
S Doradus is the brightest star in the Large Magellanic Cloud, a satellite of the Milky Way. A hypergiant, it is one of the most luminous stars known , but so far away that it is invisible to the naked eye.This star belongs to its own eponymous S Doradus class of variable stars S Doradus is the...
, the brightest star of the Large Magellanic Cloud
Large Magellanic Cloud
The Large Magellanic Cloud is a nearby irregular galaxy, and is a satellite of the Milky Way. At a distance of slightly less than 50 kiloparsecs , the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal and Canis Major Dwarf Galaxy lying closer to the center...
. They exhibit long, slow changes in brightness, punctuated by occasional outbursts in brightness during substantial mass loss events (e.g. Eta Carinae, P Cygni
P Cygni
P Cygni is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in Uranometria as a nova....
). They are extraordinarily rare. The General Catalogue of Variable Stars
General Catalogue of Variable Stars
The General Catalogue of Variable Stars is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and third editions were published in 1958 and 1968; the fourth...
only lists 20 objects as SDor.
LBVs can shine millions of times brighter than the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
and, with masses up to 150 times that of the Sun, approach the theoretical upper limit for stellar mass, making them among the most luminous, hottest and most energy-releasing star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s in the universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
. If they were any larger, their gravity would be insufficient to balance their radiation pressure and they would blow away the excess mass through stellar wind. As they are, they barely maintain hydrostatic equilibrium
Hydrostatic equilibrium
Hydrostatic equilibrium or hydrostatic balance is the condition in fluid mechanics where a volume of a fluid is at rest or at constant velocity. This occurs when compression due to gravity is balanced by a pressure gradient force...
because their stellar wind
Stellar wind
A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.Different types of stars have...
constantly ejects matter, decreasing the mass of the star. For this reason, there are usually nebula
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...
e around such stars, created by these outbursts; Eta Carinae is the nearest and best-studied example. Because of their large mass and high luminosity, their lifetime
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
is very short — only a few million years.
Current theory holds that LBVs are a stage in the evolution of very massive stars required for them to shed excess mass. They may evolve to Wolf-Rayet Star
Wolf-Rayet star
Wolf–Rayet stars are evolved, massive stars , which are losing mass rapidly by means of a very strong stellar wind, with speeds up to 2000 km/s...
s before exploding into supernovae. If the star does not lose enough mass, it may undergo a particularly powerful supernova created by pair-instability
Pair-instability supernova
A pair-instability supernova occurs when pair production, the production of free electrons and positrons in the collision between atomic nuclei and energetic gamma rays, reduces thermal pressure inside a supermassive star's core...
.
Some models suggest that LBV 1806-20 or the Pistol Star
Pistol Star
The Pistol Star is a blue hypergiant and is one of the most luminous known stars in the Milky Way Galaxy.It is one of many massive young stars in the Quintuplet cluster in the Galactic Center region....
may be the most luminous stars known. Outburst by LBVs can produce Supernova impostors.
List of LBVs
- Eta Carinae
- Pistol StarPistol StarThe Pistol Star is a blue hypergiant and is one of the most luminous known stars in the Milky Way Galaxy.It is one of many massive young stars in the Quintuplet cluster in the Galactic Center region....
- LBV 1806-20
- P CygniP CygniP Cygni is a variable star in the constellation Cygnus. The designation "P" was originally assigned by Johann Bayer in Uranometria as a nova....
- S DoradusS DoradusS Doradus is the brightest star in the Large Magellanic Cloud, a satellite of the Milky Way. A hypergiant, it is one of the most luminous stars known , but so far away that it is invisible to the naked eye.This star belongs to its own eponymous S Doradus class of variable stars S Doradus is the...
- HD 269858 (= R127)
- HD 269006 (= R71)
- AG CarinaeAG CarinaeAG Carinae is a star in the constellation Carina. It is classified as a luminous blue variable and is one of the most luminous stars in the Milky Way. The large distance and intervening dust mean that the star is not visible to the naked eye; its apparent brightness varies irregularly between...
- Wray 17-96Wray 17-96Wray 17-96 is a very luminous star in the Scorpius constellation, about away. Likely a luminous blue variable , it has an absolute bolometric magnitude of −10.9 , making it one of the most luminous stars known. Wray 17-96 is also notable for its gas hull, once thought to be a planetary nebula....
- AF Andromedae
- AE Andromedae
- HD 5980HD 5980HD 5980 is a binary star in NGC 346 nebula. It is one of the brightest stars in the Small Magellanic Cloud, and one of the most luminous stars known. HD 5980 A is probably a luminous blue variable of about 40–60 solar masses, while HD 5980 B is an evolved Wolf–Rayet star of about 30 solar masses....
- Sanduleak -69° 202; no longer exists: the star exploded as SN 1987ASN 1987ASN 1987A was a supernova in the outskirts of the Tarantula Nebula in the Large Magellanic Cloud, a nearby dwarf galaxy. It occurred approximately 51.4 kiloparsecs from Earth, approximately 168,000 light-years, close enough that it was visible to the naked eye. It could be seen from the Southern...