Luminous blue variable
Rare, massive stars with dramatic, unpredictable brightness variations.
Luminous blue variables are a rare type of massive, evolved star whose spectra and brightness shift unpredictably, sometimes dramatically. They are also called S Doradus variables, named after S Doradus, a very bright star in the Large Magellanic Cloud.
The stars P Cygni and η Carinae were known as unusual variables as far back as the 17th century, but their true nature was not clarified until the late 1900s. In 1922, John Charles Duncan published the first three variable stars ever found in another galaxy—variables 1, 2, and 3 in M33. Edwin Hubble followed up in 1926 with three more in M33 (A, B, and C), and in 1929 he added a list of variables in M31. Later, in 1953, Hubble and Allan Sandage conducted a detailed study of Var A, Var B, Var C, and Var 2 in M33, along with Var 19 in M31. Var 1 was excluded because it was too faint, and Var 3 had already been classified as a Cepheid. At the time, these were simply called irregular variables, though they stood out as the brightest stars in their galaxies. The original Hubble–Sandage paper included a footnote suggesting S Doradus might be the same type, but with strong reservations, so the connection took decades to confirm.
These five stars later became known as Hubble–Sandage variables. In the 1970s, Var 83 in M33, plus AE Andromedae, AF Andromedae (Var 19), Var 15, and Var A-1 in M31 were added to the list. Several authors described them as "luminous blue variables," though this was not yet a formal name. Their spectra showed P Cygni profiles and were compared to η Carinae. In 1978, Roberta M. Humphreys studied eight variables in M31 and M33 (excluding Var A), calling them luminous blue variables and linking them to the S Doradus class. In 1984, at an IAU symposium, Peter Conti formally grouped S Doradus variables, Hubble–Sandage variables, η Carinae, P Cygni, and similar stars under the term "luminous blue variables," shortened to LBV. He also distinguished them clearly from Wolf–Rayet stars.
Variable star types are usually named after the first discovered member, like δ Sct variables. The first LBV identified as a variable was P Cygni, so these stars were sometimes called P Cygni type variables. However, the General Catalogue of Variable Stars worried about confusion with P Cygni profiles (which appear in other star types) and chose the acronym SDOR for "variables of the S Doradus type." The term "S Dora
- type
- Variable star class
- first_identified_as_variable
- P Cygni (17th century)
- formal_name_coined
- Luminous blue variable (1984, by Peter Conti)
- acronym_in_GCVS
- SDOR
- typical_luminosity_range
- 250,000 to over 1,000,000 L☉
- typical_temperature_range
- 8,500 K to 25,000 K
- known_for
- Unpredictable outbursts and giant eruptions, some mistaken for supernovae
Lore & Background
Later papers referred to these five stars as Hubble–Sandage variables. In the 1970s, Var 83 in M33 and AE Andromedae, AF Andromedae (=Var 19), Var 15, and Var A-1 in M31 were added to the list and described by several authors as 'luminous blue variables', although it was not considered a formal name at the time. In 1978, Roberta M. Humphreys published a study of eight variables in M31 and M33 (excluding Var A) and referred to them as luminous blue variables, as well as making the link to the S Doradus class of variable stars. In 1984 in a presentation at the IAU symposium, Peter Conti formally grouped the S Doradus variables, Hubble–Sandage variables, η Carinae, P Cygni, and other similar stars together under the term 'luminous blue variables' and shortened it to LBV. He also clearly separated them from those other luminous blue stars, the Wolf–Rayet stars.
Reader's Guide
Luminous blue variables are significant because they represent a brief, unstable phase in the lives of the most massive stars, during which they shed large amounts of mass before exploding as supernovae. Their unpredictable outbursts and giant eruptions—some so violent they were initially catalogued as supernovae—provide critical insights into stellar evolution and mass loss. The class unifies historically known objects like η Carinae and P Cygni with extragalactic variables discovered by Hubble and Sandage. The term 'luminous blue variable' was formalized in 1984, but the stars themselves have been observed for centuries. Their study helps constrain models of how stars with initial masses above 20 solar masses end their lives. The two observed groups—one with luminosities above 630,000 L☉ and another below 400,000 L☉—may represent different evolutionary paths, though this is disputed. Their rapid evolution on observable timescales makes them unique laboratories for testing stellar physics.
Did You Know?
- The first luminous blue variable identified as a variable star was P Cygni, known since the 17th century.
- The General Catalogue of Variable Stars uses the acronym SDOR for 'variables of the S Doradus type' to avoid confusion with P Cygni profiles.
- Some LBV giant eruptions were initially catalogued as supernovae, such as SN 2009ip, which later evolved into a true supernova.
- The most luminous LBV, η Carinae, reaches a luminosity of 4.6 million times that of the Sun.
More in Stars And Stellar Phenomena 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record