The universe is vast and full of mysteries to modern humanity. Where is the biggest star in this universe?
First, an example close to a gigantic perfect score is Jupiter, the largest planet in the solar system. Jupiter is 11 times the size of Earth and 317 times the weight. Larger than Jupiter is a brown dwarf. A brown dwarf is 13 to 90 times more massive than Jupiter.
The second largest stars following brown dwarfs are main sequence stars. When gases such as hydrogen and helium gather over a certain mass, the center reaches a high enough temperature to cause combustion. The result is a proton-proton chain reaction, a type of fusion reaction in which hydrogen is converted to helium at the core, releasing a huge amount of energy. Main-sequence stars emit strong light due to higher temperatures and shorter lifespans as their mass increases.
When the hydrogen in the core is depleted by the proton-proton chain reaction, the main sequence star grows to a size of hundreds of thousands of times at once and then dies. At the same time, it is important to keep in mind that even if you compare the size of a star, you can compare the size of an adult to a child because the size of the star changes throughout its lifetime. The smallest of the main sequence stars, a red dwarf is 100 times more massive than Jupiter. Because red dwarfs have a small mass, large fusion reactions do not occur. Therefore, the light it emits is very weak and does not become gigantic until death.
Red dwarf stars have a lifespan of 10 trillion years, making them the most abundant star in the universe. Since the universe was created by the Big Bang 13.8 billion years ago, 10 trillion years is 1,000 times the age of the universe.
The second largest main sequence star following a red dwarf is a sun-like star. The surface temperature of the sun is 6,000 degrees Celsius, and the light it emits is strong, but its lifespan is only regarding 10 billion years.
Speaking of stars larger than the sun, Sirius A is the brightest star visible on Earth except for the sun. Sirius A has twice the mass of the Sun, 1.7 times the radius of the Sun, and 25 times brighter than the Sun. On the other hand, the series A lifespan has dropped significantly to around 2.5 billion years.
Hadar is 10 times the mass of the Sun, 13 times the size, and has a surface temperature of 25,000 degrees Celsius, and emits 20,000 times more light than the Sun. On the other hand, life expectancy is only regarding 20 million years.
The most massive star ever discovered is R136a1. R136a1 has a mass of 315 times that of the Sun and its brightness is 9 million times that of the Sun. However, the size difference is small compared to the mass and brightness, and R136a1 is regarding 30 times larger than the sun. Lifespan is in the order of millions of years. R136a1 is expected to lose mass at a rate of 32.1 tons per second, due to the massive loss of mass by the stellar winds. R136a1 is believed to have been formed by the coalescence of a massive planet.
So far, stars are consistently proportional to mass and size. But for larger stars, dilation becomes an important factor. In main-sequence stars, when hydrogen is scarce in the nucleus, the fusion efficiency in the nucleus decreases, the nucleus is compressed, and the temperature and pressure rise. As a result, the outer layer of a star expands over time because of the increased external energy.
Gacrux, for example, has regarding 1.3 times the mass of the Sun, but a radius of 84 times that of the Sun. Meanwhile, just before the sun dies, its radius is expected to expand 200 times. If it expands to a radius of 200 times, it is expected to swallow Mercury and Venus.
The largest star in the universe, the Hypergiant, boasts an incomparable size of this expanded sun. A hypergiant is said to be very bright and is said to be exuding a large amount of mass from a surface with weak surface gravity.
A pistol star has 25 times the mass of the Sun but 300 times the radius. Its lifetime is difficult to predict, but it can be seen in the millions of years and is classified as a bright blue variable star because it emits blue light.
Yellow hypergiants are larger than bright blue variable stars such as Pistol. The yellow hypergiant under study is the constellation Cassiopeia, which is bright enough to be detected with the naked eye even though it is 1,000 light-years away from Earth. In the constellation Cassiopeia, it has 40 times the mass of the Sun, 500 times the radius, and 500,000 times the brightness. If moved from Cassiopeia to the same position as the sun, mankind would burn to death. Yellow hypergiants are rare and only 15 have been discovered so far. This means that yellow hypergiants have short lifetimes.
Red hypergiants are larger than yellow hypergiants. As long as red hypergiants are observed, there may be no more large stars. After all, if you ask what the largest star in the universe is, the exact answer is that you don’t know. A star classified as a red hypergiant is bright but far away from Earth, so even a small measurement error can lead to a large measurement error. In addition, red hypergiants are difficult to measure because they are comparable in size to the solar system and emit a large amount of mass. Therefore, as science and technology advance and measuring instruments themselves improve, the answer to the question of being the largest star in the universe is expected to change.
The largest ever discovered is Stephenson 2-18. Stevenson 2-18 was thought to have had several times the mass of the Sun at birth, but lost half of its mass. While the average red hypergiant is considered to have a radius of 1,500 times that of the mass Sun, Stevenson 2-18 appears to have a radius of 2,150 times that of the Sun and 500,000 times the brightness of the Sun.
It takes 8.7 hours at the speed of light to circumnavigate Stevenson 2-18. The SR-71, the fastest aircraft in human history, nicknamed the Blackbird, takes nearly 500 years to circumnavigate. If Stevenson 2-18 is present at the position of the sun, the surface will reach Saturn.
As Stevenson 2-18 continues to emit mass, its temperature continues to rise, causing heavy metals to accumulate in its core. Stevenson 2-18 will eventually cause a supernova explosion, spreading heavy metal-laden gas into space. The cycle begins anew, such as stars being born or killed by the scattered gas.
