[이광식의 천문학+] How big is the largest star in the universe? Supergiant ‘Stevenson 2-18’ : ZUM News



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Comparison of the size of the sun and Stevenson 2-18

It would be interesting and meaningful to refine our cosmic sense of ‘size’. First, if we have to pick up the biggest object around us, it is definitely the sun. It is 109 times larger in diameter than Earth, where 8 billion people live, and 1.3 million times its volume. The sun is an absolute existence in the solar system to the extent that it is awkward to say that the sun rules the solar system. It accounts for 99.86% of the mass of all celestial bodies in the solar system.

Even such a sun is nothing more than a dwarf if taken out into the galaxy and into space. That is why there are so many huge stars in the universe. Stars of such enormous size are called supergiants, and even the familiar supergiant Betelgeuse in the constellation Orion is well over 1000 times the diameter of the Sun. If this star were dragged into the Sun, it would be nearly the size of Jupiter’s orbit.

However, it is not uncommon for stars to treat Betelgeuse as petty. VY Canis Majoris (VY Canis Majoris), discovered in the constellation Canis Major, was confirmed to be 2069 times that of the Sun as a result of observations in 2020. It is larger than Saturn’s orbit. Although it was once known as the largest star in the history of observation, more sophisticated observations show that the radius is much smaller than that of previous measurements. It is about 3900 light-years from Earth.

A hypergiant has emerged that has clearly overtaken VY Canis Major to become the largest star, a star called Stevenson 2-18 discovered in 1990 by American astronomer Charles Bruce Stevenson.

Seoul Newspaper

The brightest and reddest star in the center is Stevenson 2-18. The bright stars above are the Stevenson 2 star cluster.

One of 40 red supergiants in the open cluster Stevenson 2, it is located in the constellation Shields, about 20,000 light-years from Earth. It does not belong to the arm of Orion, the spiral arm to which the Earth belongs, but to a completely different arm, the Shield-Crucius Arm.

So how big is this star? It has a diameter of about 2.9 billion km, which is 2150 times that of the Sun. It would take more than 8 hours to revolve around this star at the speed of light, and it would take 1,100 years to travel around the star at a speed of 900 km/h. It far exceeds the period of the Goryeo Dynasty and the Joseon Dynasty combined. If this star were dragged into the Sun’s place, it would swallow up Saturn’s rings and moons. Can you imagine that one thing could be that big? Of course, this star belongs to the Milky Way, but astronomers generally firmly believe in the isotropy and uniformity of the universe, meaning that it is not too much to consider as the largest star in the universe.

The largest star in the universe, Stevenson 2-18, is about 14-20 million years old, similar to other stars in the cluster, making it very young compared to other stars. As stars grow, their lifespan decreases exponentially. This is because the larger the star, the faster nuclear fusion proceeds, which consumes an enormous amount of nuclear fuel.

Stevenson 2-18 is predicted to die out in a supernova explosion in millions of years, and then become a black hole.

Kwangsik Lee Science Columnist joand999@naver.com

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