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Some of the typical supergiants that have been observed

A supergiant star is a star with a large luminosity and volume, and the brightness is the largest in the universe. We can see them with the naked eye in the night sky of the Earth, but we don't know that they are supergiants.

The luminosity of a supergiant is significant, indicating that its surface area is significantly larger than that of a non-supergiant of the same spectral type. Supergiants are generally 25-500 times larger than the Sun, and some red supergiants can be more than 1,500 times larger than the Sun. But they are generally only 10 to 50 times the mass of the Sun, so they are much less dense than the Sun. The average density of a giant star can be compared to the density of gas on the ground, while the density of a supergiant is only one thousandth the density of water, which is an interesting phenomenon. It turns out that the giants of the stellar world are actually behemoths with nothing on the surface.

The most typical and brightest blue (hot) supergiants seen with the naked eye on Earth are Betelgeuse and Tianjin IV; The brightest red (cold) supergiants are Betelgeuse (see the yellow star on the upper left in the image on the right) and Antares. The mass of a supergiant star is thought to be greater than 5 solar masses. Since stars of the same spectral type have the same surface temperature, they must have the same radiant energy rate per unit surface area.

What are the typical blue supergiants?

Blue supergiants (BSGs) are the first level of the spectral classification of stars, and they are of type O or B, which is one of the supergiants. They are very hot and bright, with a surface temperature of 10,000-50,000°C and a mass of more than 10 times that of the Sun. The most representative blue supergiant is Betelgeuse VII in the constellation Orion, along with SN1987A, Supernova 1987A and Tianjin IV.

blue supergiant

Betelgeuse is the most typical blue supergiant, he is the β of Orion, whose English name is Rigel, with a luminosity of 40,000 times that of the Sun, and is the seventh brightest of the twenty brightest stars in the day, and the brightest blue supergiant. The apparent magnitude is 0.18, the absolute magnitude is -6.93, and it is about 863 light-years from Earth. Its spectral type belongs to B8, and in terms of the stellar stage, Betelgeuse is a supergiant star. In terms of star size, Betelgeuse is a blue supergiant with 55,000 times the luminosity of the Sun, making it the brightest star in the constellation Orion.

Deneb (Swan α, αCyg) is the main star of the constellation Cygnus, the 19th brightest star of the day, with an apparent magnitude of 1.21-1.29 and an absolute magnitude of -8.37, at a distance of 2640 light-years. It is blue-white in color and is a white supergiant of type A2Ia. The luminosity is 180,000 times that of the Sun, the surface temperature is 8500 K, the radius is 187 to 220 times that of the Sun, and the mass is 19.6-23.0 times that of the Sun.

What are the typical red supergiants?

Red supergiants, like other stars, combine hydrogen to form helium during the main-sequence period, but stars have shorter lifespans. The core of a star 15 times the mass of the Sun will run out of hydrogen in 10 million years. Due to its massive mass, the temperature and density at its core are high enough that helium combines into carbon and forms a hydrogen combustion shell at the same time. The helium core burns steadily because the star's gravitational pull is large enough to control it. Because the heat is generated by the core, the outer part of the star expands larger than the red giant, forming the red supergiant. The most typical red supergiants are Betelgeuse, Antares, and Eclipse Binary.

Red supergiant

Betelgeuse is a red supergiant in the constellation Orion, with a radius between 700 and 1,000 times that of the Sun, and if placed in our Sun, it would surpass Jupiter on the periphery. The change in radius causes its luminosity to change with it, with brightness varying from 0.4 to 1.3. It's about 500 light-years away, and because it's so close and big, it's the first time humans have been able to resolve a star the size of a surface other than the Sun. Betelgeuse is nearing the end of its life and is speculated to be a supernova in the next few million years.

Antares, the star α Scorpio (the main star of Scorpio), is the loneliest first magnitude star of the whole day, but there are many bright second-magnitude stars in its vicinity. In ancient China, it was also known as the Great Fire, which belonged to the Antares of the Seven Nights of the Eastern Canglong and was used to determine the seasons. "July Flowing Fire" means that Mars is heading westward, and the weather will be cold. Antares, the fifteenth brightest star of the day, is a visual binary star with an apparent magnitude of 1.2 for the main star, a red supergiant of type M1I with a luminosity of 10,900 times that of the Sun, and a companion star with a blue dwarf star of magnitude 5.4 and an angular distance of 3". The composite magnitude is 0.96, and the absolute magnitude is -5.28. The star belongs to the Scorpio-Centaur constellation, so the known distance is 430 light-years. Modern astronomy is known as the "Scorpio α Stars". It is a red supergiant.

What are the typical yellow supergiants?

Yellow supergiant

Yellow supergiants (YSG) are supergiants with a spectral type of F or G. This type of star has a mass between 15 and 20 solar masses, and like other supergiants, depending on the chemical elements consumed in their core, making them change color in stages between blue and red as they age. To date, only a handful of supergiants have spent long enough in the yellow phase. There may be only a few rare supernovae associated with the system of yellow supergiants, and only two such supernovae have been detected, and most supergiants become supernovae in the blue (high-heat) phase or the red (low-temperature) phase.

There are many supergiant stars of various colors in the vast universe, so let's continue to look forward to further exploration by astronomers to give us more shocks.