Luminous blue variable

Some stars are very big and bright.

These stars are called blue variables. They do not shine the same way every day. They can have big bursts of light.

During a burst, the star gets much brighter. It also loses a lot of its weight. These stars live for a very short time. They will eventually explode in a huge flash.

It is amazing to watch these giant stars.

Some stars are massive and very bright. We call these luminous blue variables, or LBVs.

These stars do not shine steadily. Instead, they change in brightness and color. This happens in a way that is hard to predict.

LBVs are much bigger than our Sun. Some are over a million times brighter. They also lose a lot of their mass. This mass loss can happen in big bursts. These are called giant eruptions.

Some eruptions are so large that they look like a supernova. A supernova is a massive star explosion. Because of these bursts, LBVs often have clouds of gas around them. We call these clouds nebulae.

These stars live very fast lives. They only live for a few million years. The LBV stage is just one part of their life. Most models show that all LBVs will eventually explode. They end their lives as supernovae.

One famous example is the star Eta Carinae. It is a very bright and well-studied LBV.

Luminous blue variables, or LBVs, are rare and massive stars.

These stars are very bright and show unpredictable changes. Their brightness and color change in ways that are hard to predict. They are often called S Doradus variables after a very bright star. These stars are much larger and brighter than our Sun. Some LBVs are over a million times more luminous than the Sun. They are some of the most luminous stars in the universe.

An LBV goes through different stages of brightness. In a quiet state, they are typically B-type stars. During a normal outburst, the star's temperature drops to about 8,500 K. This change makes the star look brighter to our eyes. Some stars have short cycles that last less than 10 years. Other stars have longer cycles that take more than 20 years. These outbursts might happen because of changes in helium opacity.

Scientists have studied these strange stars for a long time. People knew about stars like P Cygni and Eta Carinae in the 17th century. In 1922, John Charles Duncan found the first variable stars in another galaxy. Edwin Hubble found more of these stars in 1926 and 1929. Hubble and Allan Sandage studied them again in 1953. In 1978, Roberta M. Humphreys linked them to the S Doradus class. Finally, Peter Conti used the name "luminous blue variable" in 1984.

These stars are very massive and live very short lives. An LBV stage lasts much less than a million years. Some LBVs are extremely huge and heavy. For example, Eta Carinae can reach 4.6 million times the Sun's luminosity. Other stars might have masses that approach or even exceed 100 solar masses. The least luminous ones have masses as low as 10 solar masses. These stars lose a lot of their mass through stellar winds.

Most scientists believe that all LBVs will eventually explode. They are likely a final stage before a star becomes a supernova. A supernova is a massive star explosion. Some LBVs undergo giant eruptions that look like supernovae. These are sometimes called supernova imposters. These big bursts can create large clouds of gas called nebulae.

You can see these beautiful clouds around stars like Eta Carinae.

Luminous blue variables, often called LBVs, are rare and massive stars.

These stars are highly evolved and show unpredictable changes in their brightness and spectra. They are also known as S Doradus variables. This name comes from S Doradus, a very bright star in the Large Magellanic Cloud. LBVs are among the most luminous objects in the universe. They are unstable supergiants or hypergiants. Their extreme brightness and mass make them critical to understanding how the largest stars live and die.

An LBV undergoes specific physical changes during its life. In a quiescent state, which means a quiet or stable period, these stars are typically B-type stars. During this phase, they can be quite hot. When an LBV enters a normal outburst, its temperature actually decreases to around 8,500 K. This temperature is slightly hotter than yellow hypergiants. Even though the temperature drops, the bolometric luminosity, or total energy output, usually remains constant. However, because the temperature changes, the visual brightness can increase by one or two magnitudes.

Some 3-D simulations suggest these outbursts might be caused by variations in helium opacity. Opacity refers to how much a material blocks light.

There are different types of cycles that these stars exhibit. Some LBVs show strong-active cycles. These are periodic outbursts that can last longer than 20 years or less than 10 years. Other stars show weak-active cycles. These variations are much smaller, often less than half a magnitude. Weak-active cycles always occur on shorter timescales of less than 10 years. Additionally, some LBVs undergo giant eruptions. These eruptions involve much larger increases in luminosity and mass loss. These events can be so violent that they were once mistaken for supernovae.

Astronomers have been studying these unusual stars for centuries. People noticed stars like P Cygni and Eta Carinae in the 17th century. In 1922, John Charles Duncan published the first detection of variable stars in an external galaxy. Edwin Hubble found more in the Triangulum Galaxy in 1926 and 1929. In 1953, Hubble and Allan Sandage conducted a detailed study of several of these stars. They were originally called Hubble–Sandage variables. In 1978, Roberta M. Humphreys linked these stars to the S Doradus class. Finally, in 1984, Peter Conti formally grouped these stars under the term "luminous blue variable."

The scale of an LBV is truly massive. The most luminous LBVs can be over a million times brighter than the Sun. For instance, Eta Carinae reaches 4.6 million times the Sun's luminosity. Their masses are also extreme. Some may approach or even exceed 100 solar masses. The least luminous LBVs have luminosities around 250,000 times that of the Sun. These smaller LBVs have masses as low as 10 solar masses. However, they were likely much more massive when they were on the main sequence. This is because they lose mass very quickly through stellar winds and outbursts.

LBVs are in a very rapid stage of stellar evolution. Their total lifetime is only a few million years. The LBV phase itself lasts much less than a million years.

Models suggest the LBV stage is a way for massive stars to shed excess mass. This might happen during core hydrogen burning or hydrogen shell burning. Some models suggest LBVs are the final stage before a star becomes a Wolf–Rayet star. This is a stage where the star has lost much of its hydrogen. The LBV phase is analogous to the red giant phase seen in smaller stars.

Most scientists believe that nearly all LBVs will eventually explode as supernovae. Some LBVs undergo giant eruptions that create nebulae, which are large clouds of gas. Eta Carinae is a famous example that produced the Homunculus Nebula.

Some of these eruptions are called supernova impostors. This is because they look like a star exploding, but the star actually survives. However, some stars may explode directly as a supernova while in the LBV stage. For example, the progenitor of SN 2005gl was an LBV in outburst just years before it exploded. These stars are a vital link in the life cycle of the universe's most massive objects.