How big are the known stars in the universe?

Humankind’s journey of exploring the universe is endless, and every scientific discovery refreshes people’s cognition.

Today, the throne of the largest star in the universe has been replaced again. Its diameter is 3 billion kilometers, equivalent to 0.3 thousandths of a light year.

However, even such a huge object does not reach the diameter of 1 light year. What celestial bodies in the universe have a diameter exceeding 1 light year?

The largest star in the universe

Previously, the astronomical community has always believed that UY Scuti is the largest star currently observed by humans. It is about 9,500 light-years away from the Earth and has a diameter of more than 2.37 times 10^9 kilometers.

What is this diameter? If UY Scuti were placed in the solar system, its surface would directly engulf the orbit of Jupiter, and the Earth would also be swallowed by it.

However, UY Scuti is dwarfed by Stevenson 2-18.

In 1990, scientist Stevenson accidentally discovered the photosphere of Stevenson 2-18 while observing the universe using infrared rays.

The star was gradually recognized and named after its discoverer.

Stevenson 2-18 is about 20,000 light-years away from Earth and is 10 billion times the size of Earth.

Its diameter reaches a terrifying 3 billion kilometers.

Stevenson 2-18 is located in an open star cluster, a group of stars consisting of hundreds or thousands of stars.

It is a medium-sized celestial body in the universe, with a diameter of up to 100,000 light years, equivalent to the size of a galaxy. It is also one of the celestial bodies we are looking for with a diameter of more than one light year.

For example, the luminous spiral arms of the Milky Way are composed of multiple open star clusters, which are one of the direct sources of light and heat of the Milky Way.

Since all the stars in the cluster are below the visible light level, they are difficult to observe with the naked eye, and Stevenson 2-18 can only be seen through infrared light.

Why can't we see it with the naked eye when it is under visible light?

In layman's terms, the open cluster where Stevenson 2-18 is located has too many stars and is too bright, causing the light within it to be deceptive. It looks like a ball of light, making it difficult to detect.

It has to be said that humans discovered Stevenson 2-18 purely by luck. After all, there are countless stars in the vast universe, and the current level of human technology is unable to observe all of them.

Since Stevenson 2-18 is so huge, is it the largest star in the universe?

No one can say for sure, but as the saying goes, there are always people better than you, and there are always stars better than you. I believe that there must be stars in the universe that are thousands of times larger than ours.

Although the 3 billion kilometers diameter of Stevenson 2-18 looks terrifying, when converted into light years, it is only 0.3‰ light years!

The speed of light is 300,000 kilometers per second, and a light-year is the distance that light travels in one year. Therefore, the total distance of a light-year is approximately 946 trillion kilometers.

So, even though the number 1 light year itself is very small, when converted into the units we are familiar with, it is completely beyond everyone's imagination.

You should know that the total length of the Beijing-Shanghai Railway is only 1,463 kilometers, and it takes more than four hours for people to travel by high-speed rail at a speed of 300 kilometers per hour.

If people take high-speed rail to travel a distance of one light year, it is likely that our descendants will not be able to reach it for dozens of generations.

At this time, curious friends may ask, is there any celestial body in the universe with a diameter exceeding one light year?

Yes! Of course there is! A light year may be out of reach for humans, but for the entire observable universe, it is just a millimeter, and one of the celestial bodies is right next to us.

Oort Cloud

There has always been a debate in the scientific community about what it means to leave the solar system.

Some scientists believe that as long as humans leave the Kuiper Belt (outside the orbits of the eight planets), they will have left the solar system.

Because the Kuiper Belt is the farthest place that the sun's high-energy particles can reach, and it is also the effective range of influence of the sun's gravity.

So at the beginning of the 21st century, when the American Voyager 2 passed through the Kuiper Belt, many people happily believed that mankind had left the solar system.

Another group of scientists believes that the Oort Cloud is the boundary of the solar system.

This group of scientists proposed that the Oort Cloud is the residual matter in interstellar space when the sun was initially formed.

The Oort Cloud is affected by the cosmic redshift and is constantly expanding outward. It has now evolved into a huge celestial body.

Overall, the Oort Cloud is a huge cloud that surrounds the solar system, with its longest radius exceeding 1 light year.

The nebula is filled with comets from outer space, and it is like a protective film that protects the entire solar system.

The Oort Cloud is expanding every year, and scientists speculate that the Oort Cloud will dissipate under the gravitational influence of other stars after the end of the Sun's life.

The terrifying structure of the Antarctic wall

If the Oort Cloud's radius of more than 1 light year is shocking enough, then the next one will definitely refresh everyone's cognition again.

It is the South Pole Wall, a special celestial structure in the universe, spanning about 1.4 billion light-years and containing trillions of stars.

Compared with other celestial structures, the South Pole Wall is very close to us, only 1 billion light-years away, but humans have never been able to discover it.

It was not until the end of the 20th century that a scientific team used the principle of redshift to finally dig out this cosmic giant.

The ancients once said, "I cannot see the true appearance of Mount Lu because I am inside the mountain." There are two types of objects that are difficult for humans to observe with the naked eye.

One type is an object that is so small that it cannot be any smaller and can only be observed with the help of instruments such as microscopes.

The other type is an object that is so large that people cannot see its entirety or recognize its existence.

The South Pole Wall naturally belongs to the latter. For a long time, scientists have ignored its existence in astronomical measurements.

Why is the South Pole Wall a special structure? Because the galaxy clusters contained in it are connected by hydrogen chains, like a network of nervous systems, forming a huge whole.

This is what scientists call the cosmic web. Even scientists are unsure of what kind of substance it is.

However, the cosmic web is of vital importance in cosmology. It is the original material for studying the structure, formation and itself of the universe. Studying the evolution of the cosmic web can help scientists explore the evolution of the universe.

Scientists have also found the largest celestial structure to date through the cosmic web - the Hercules-Corona Borealis Great Wall!

The structural length of the Hercules-Corona Borealis Great Wall reaches a terrifying 10 billion light-years. It should be noted that the radius of the observable universe is only more than 40 billion light-years, and the Hercules-Corona Borealis Great Wall accounts for one-eighth of the length of the observable universe.

Astronomers estimate that the Hercules-Corona Borealis Wall covers an area of ​​approximately 10.7% of the entire observable universe.

The discovery of the Hercules-Corona Borealis Wall is related to a powerful gamma-ray burst.

The huge amount of light and energy that can be released after a star dies is called a gamma-ray burst, which is one of the most powerful celestial events known.

Previously, a gamma-ray burst illuminated a corner of the Hercules-Corona Borealis Wall, and scientists were surprised to find that such a shocking and huge structure was buried deep in the universe.

Based on this, we can boldly speculate that at the edge of the endless universe, there is a larger cosmic structure.

Perhaps our observable universe itself is part of a larger celestial structure, but we are "in it" and cannot perceive it.

With the advancement of human technology, one day we will uncover the mystery of the universe and move towards the more distant starry sky.

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