The universe is vast and full of mysteries for modern humans. "Which is the largest star in the universe?" There are always children asking this question to their parents. This article will chat about this frequently asked question.
The giant star we are most familiar with in the solar system is Jupiter , the largest planet in the solar system. Jupiter is 11 times larger than Earth and 317 times heavier.
Even larger than Jupiter is the brown dwarf . Brown dwarfs are approximately 13 to 90 times more massive than Jupiter.
Brown dwarfs have a mass between the giant planets like Jupiter and Saturn and the smallest stars. The next largest star category after brown dwarfs is main sequence stars .
When gases such as hydrogen or helium accumulate beyond a certain mass, the central part reaches high temperatures, causing combustion.
As a result, a proton-proton chain reaction, a fusion reaction that converts hydrogen into helium, occurs in the core. It generates a lot of energy. The heavier the main sequence star, the higher the temperature, the stronger the light, but the shorter its lifespan.
When the core hydrogen is exhausted by the proton-proton chain reaction, the main sequence star suddenly expands to hundreds of thousands of times larger and then dies.
Even if you say "compare the sizes of stars" in this way, you should remember that the sizes of stars change throughout their lifetimes, so think of it as "adults and children".
The smallest red dwarf in the main sequence, , has a mass approximately 100 times that of Jupiter.
Because the mass of red dwarf stars is very small, large fusion reactions will not occur. Therefore, the light emitted is very weak and never becomes massive upon death.
Red dwarfs have a lifespan of 10 trillion years, making them the most numerous stars in the universe. According to calculations, the universe was born with the Big Bang about 13.8 billion years ago, so 10 trillion years is about 1,000 times the age of the universe.
The second largest stars in the main sequence after red dwarfs are sun-like stars. The surface temperature of the sun is as high as about 6,000 degrees Celsius. Although the light it emits is very strong, its lifespan is only about 10 billion years.
Let's move on to stars larger than the sun. Sirius A, it is the brightest star seen from the earth except the sun. The mass of Sirius is twice that of the sun, and its radius is 1.7 times that of the sun. It is 25 times brighter than the sun.
However, Sirius A's lifespan, on the other hand, has dropped dramatically to about 2.5 billion years.
Beta Centauri is 10 times as massive and 13 times as massive as the Sun. The surface temperature reaches 25,000 degrees and the light emitted is 20,000 times stronger than the sun. Its lifespan is only about 20 million years.
As you can see from the examples so far, the greater the mass, the greater the size.
The heaviest star ever discovered is R136a1. R136a1 is 315 times more massive than the Sun and 9 million times more luminous.
However, the size difference is small compared to mass and brightness, with R136a1 being around 30 times larger than the Sun. Lifespan is approximately several million years.
A large amount of mass is escaping from R136a1, and it is expected to be losing mass at a rate of 32.1 kilowatts per second due to the stellar wind .
R136a1 is thought to have formed from the coalescence of supermassive planets, and the hydrogen in nuclei is expected to be exhausted within millions of years.
The above stars are always proportional in mass and size. However, when considering stars larger than this, "bloat" is an important factor.
When a main sequence star uses up hydrogen in its nucleus, the nucleus becomes compressed and the temperature and pressure increase as the efficiency of fusion in the nucleus decreases. As a result, the star's outer layers expand over time due to the increase in outward energy.
For example, the mass of Gamma Australis is about 1.5 times that of the Sun, but its radius is 84 times that of the Sun.
On the other hand, the Sun's radius is thought to have expanded by a factor of 200 before its death.
If it expanded to 200 times its radius, Mercury and Venus are expected to be swallowed up.
And it is supergiant , the largest star in the universe. Such an expanding sun is extremely large.
Supergiants are very bright, but have weak surface gravity, and it is thought that a large amount of mass flows from the surface.
Pistol star has a mass 25 times that of the Sun, but its radius is about 300 times greater. Although its lifetime is difficult to predict, it is estimated to be around millions of years, and it is classified as a high-luminosity blue variable star because it emits blue light.
Yellow supergiants are larger than high-luminosity blue variable stars such as the Pistol Star.
The most studied yellow supergiant star, Rho Cassiopeia is bright enough to be seen with the naked eye, even though it is 1,000 light-years away from Earth.
Rho Cassiopeia has a mass 40 times that of the Sun and a radius 500 times that of the Sun. Approximately 50,0000 times brighter.
If Rho Cassiopeia were in the same position as the sun, humanity would burn up.
Yellow supergiants are rare, with only 15 discovered so far. This means that yellow supergiants have a short lifespan.
Even larger than this yellow supergiant is the red giant . Yellow supergiants are the largest stars that can be observed, and there may be no larger stars.
So, which star will be the "largest star in the universe"...
The exact answer is "no one knows". This is because stars classified as yellow supergiants are so bright and so far away from Earth that even small measurement errors can lead to large errors in the measurement results.
In addition, the red supergiant is about the size of the solar system and emits a large amount of mass, making it difficult to measure. Therefore, as science and technology advance and the measuring instruments themselves improve, the answer to the question "the largest star in the universe" will change.
Stephenson 2-18 (St2-18, Stevenson 2-18) is the largest ever discovered.
Stephenson 2-18 was several times the mass of the Sun at birth, but is believed to have lost half of its total mass.
Yellow supergiants are thought to have an average radius of about 1,500 times that of the Sun, while Stephenson 2-18 has a radius of 2,150 times that of the Sun and is expected to be 50,0000 times brighter.
The sun is about the same size as chile compared to Stephenson 2-18. For humans, the size of the Stephenson 2-18 is unimaginable.
It would take about 8.7 hours to get around Stephenson 2-18 at the speed of light. The SR-71 is the fastest aircraft in human history, taking nearly 500 years to make the leap.
If Stephenson 2-18 appeared at the position of the Sun, its surface would reach Saturn.
As Stephenson 2-18 continues to release mass, its temperature continues to rise and heavy metals continue to accumulate in its core. Stephenson 2-18 is thought to eventually cause a supernova explosion, spewing gas containing heavy metals into the universe.
The scattered gas begins a new cycle in which new stars are born and die.
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