Facts About Blue Supergiant Stars

These stars can transform into red supergiant stars before eventually exploding during the supernova event. Here are few interesting facts about blue supergiant stars.

According to astronomers, a blue supergiant star can fluctuate between the blue supergiant and red supergiant phases. These stars eventually explode at the time of the supernova event.

Our universe is formed of stars, planets, nebulae, galaxies, etc. Stars are important constituents of the universe. In fact, they attain the central role and position in cosmic bodies, owing to the energy that they produce. If we talk about stars, there is great variety observed in their luminosity, surface temperature, size, etc.

A star is basically a luminous sphere of plasma. The plasma is held together by gravity. The Sun is the nearest star to the Earth. There are many bigger and more luminous stars than the Sun in the universe.

Blue supergiant stars are amongst the largest and brightest stars in the world. They are characterized by high temperatures ranging from 20,000 - 50,000 kelvin (35,540.3 - 89,540.3 °F). These bright and hot stars are roughly the size of 20 solar masses. However, their size can vary a lot. A blue supergiant star can be as big as 1,000 solar masses.

Blue supergiants are highly luminous stars formed as a result of stellar evolution. The process of stellar evolution continues for millions of years. The lifespan of a blue supergiant star can be up to 10 million years. Some more interesting facts are presented below.

Blue supergiant stars are known for the fast stellar winds which blow on their surfaces. However, these winds, although fast, occur sparsely.

These stars have short lifespans in comparison to most stars; which is why they are found in cosmic structures such as spiral galaxies and open clusters. These structures are younger in comparison to other cosmic structures.

Blue supergiant stars are of rare occurrence in comparison to other kinds of stars. However, the luminosity of these stars makes them easily visible.

Stars that rotate at a fast pace are known to contain high proportions of helium. These stars also exhibit a mixture of different kinds of elements.

Blue supergiant stars have heavy elements in their spectra. The quantities of heavy elements vary with the age of the star. Another factor which determines the quantity of heavy elements is the efficiency with which nucleosynthesis products are convected from the core of a star to its surface.

The process of their evolution is a bit complicated to understand. Even after years of research, the process is not completely understood, till date.

Recently, a blue supergiant star was discovered by astronomers Dr. Youichi Ohyama (Institute of Astronomy and Astrophysics, Academia Sinica or ASIAA, Taiwan) and Dr. Ananda Hota (UM-DAE Center for Excellence in the Basic Sciences or CBS, India). This star emerged 55 million years ago.

Information about some of the notable blue supergiants is given here. Here is a representative image of the Rigel star and the Sun.

The Rigel, also known as Beta Orionis, is a blue-white supergiant star. In the night sky, it is the 7th brightest star. Placed in the category of first magnitude stars, Rigel is the 3rd most inherently luminous star after Deneb and Betelgeuse. It is located at a distance of roughly 870 light years from the Sun.

• Constellation: Orion
• Luminosity (bolometric): 1.26 +0.37/-0.29 ×10^5 L☉ (Solar Luminosity).
• Radius: Estimated radius of Rigel is 74 R☉ (solar radius).
• Temperature: 12,130 K (Kelvin)

The 29 Canis Majoris is a binary star which belongs to the Beta Lyrae variable class. A binary star is formed of two stars which revolve around a common center of mass. As per parallax measurements, the star is located at a distance of 3,000 light years from the Earth.

29 Canis Majoris is a distant member of the NGC 2362 open cluster.

• Constellation: Canis Major
• Luminosity: 200,000 / 63,000 L☉
• Radius: 13 / 10 R☉
• Temperature: 33,750 / 29,000 K

The Zeta Puppis, also known as Naos, was earlier believed to be a part of the Vela star-forming region. However, as per parallax measurements taken in 2008, this star is not a part of the Vela region. Also, it is understood that the star is much closer to the Earth.

In terms of apparent magnitude from the Earth, Zeta Puppis is the 62nd most luminous star.

• Constellation: Puppis
• Luminosity: 550,000 L☉
• Radius: 14 L☉
• Temperature: 42,000 K

These stars are created from clouds of gases and dust. The clouds collapse into O class and early B class stars. The O class and B class stars evolve into blue supergiants in a few million years. The main sequence is the longest phase in the life of a star.

• In the main sequence phase, a star is characterized by the process of nuclear fusion. The process is also known as proton-proton chain. Apart from the nuclear fusion process, Carbon-Nitrogen-Oxygen (CNO) cycle can also take place in high mass stars.

• Once the hydrogen in these stars gets depleted, their core collapses. It causes heating up of the core. As the core begins to heat up, the outer layers of the star begin to expand. Stars with low or medium mass become red giants; those stars with a high mass get converted into red supergiants.

• The core of high mass stars serves as a platform for the fusion of helium into oxygen and carbon. The process takes place at a rapid pace. In this process, the surface of the star becomes red, because its temperature is lower than that of the core. At this stage, the surface temperature of the star is between 3,500 K and 4,000 K.

• Different elements get fused in the core of these stars. It causes the rate of fusion to vary greatly. When fusion takes place at a slower pace, the star undergoes contraction and turns into a blue supergiant. The blue supergiant stars which evolve from the main sequence phase are characterized by high mass loss rates, high luminosities, and instability.

Some of the main sequence stars, instead of transitioning into the blue supergiant phase, directly evolve into Wolf-Rayet stars - evolved and high mass stars. These stars are amongst the brightest, biggest, and also the most short-lived ones. Owing to their unique nature, studying blue supergiants is an interesting activity.