The diameter of the largest star in the universe is 3 billion kilometers, and its volume is about 10 billion times that of the sun. It is a real "behemoth". But when we change its unit to light years, we can find that it is only 
.3‰ light years.
So, who is this largest known star? Are there any celestial bodies in the universe with a diameter of more than 1 light year?
There are many celestial bodies in the universe
Who is the largest star?
For a long time, although humans can't fly much, they can see very far.
In addition to looking for alien signals and habitable planets, scientists also paid special attention to the situation of some massive stars in the universe. After all, stars do not exist forever, and observing the changes of other stars will help us predict future situations.
The largest known star in humans is Stevenson 2-18 (Stephenson 2-18) , which was discovered by an American astronomer in the 1990s.
The largest known star Stevenson 2-18
At that time, the astronomer first discovered an open cluster , and then found the red supergiant star in the cluster.
According to estimates, the diameter of Stevenson 2-18 is 3005015000 kilometers, which is generally recorded as 3 billion kilometers. This number doesn't seem to be very big, but if this guy was stuffed directly into the solar system to replace the sun, the earth would have long become its "object".
Because, the orbit of Stephenson2-18 can easily extend to Saturn near .
Stevenson 2-18 and the volume of the sun
Of course, as a red superstar, Stevenson is not only very expanding, but also has a dazzling brightness, about 3700 sun luminosity , and the spectral type is M6.
Scientists were surprised after finding this speculative value because Stevenson confirmed to people 2-18 that the red superstar model we built in the past was still "insufficient imagination." In the real universe, there are stars larger and brighter than the model.
Red superstar model established by scientists
However, it should be noted that although Stevenson 2-18 looks very outstanding in all aspects, especially in terms of body shape, he threw stars such as Shield UY, Cygnus NML behind his butt, but when we change the unit defined by its diameter to light years, we will find that this guy seems to have become smaller again, because its diameter is only 0.3‰ light years .
light-year as a unit of length is the distance after light travels for a year at a speed of about 300,000 kilometers per second. Therefore, if converted in kilometers, one light year can be obtained, which is equal to 9460730472580 kilometers, which is about 0 trillion kilometers .
1 The length of light-year is actually very amazing
Compared with 10 trillion kilometers, Stevenson's diameter of 3 billion kilometers is really nothing. Through this comparison, you may also realize how terrifying the distance of 1 light year is.
So, is there any celestial bodies in the universe with a diameter of 1 light year?
Are there celestial bodies with a diameter of more than 1 light year in the universe?
First of all, we need to clarify what the definition of "celestial body" is.
celestial bodies refer to all the naturally formed material entities in observable universe . Simply put, they are all individuals in the universe. This broad definition makes the celestial bodies contain a lot of things, such as stars, galaxies, dwarf planets, comets, , galaxies, star clusters, , nebula and interstellar matter , etc., all belong to celestial bodies.
celestial bodies include not only stars and planets
and even said that radio power supply, infrared source , etc. discovered by people through radio detection, are also considered one of celestial bodies.
If we want to subdivide it in detail, celestial bodies can also be divided into solar system celestial bodies and extra-solar system celestial bodies .Among them, the celestial bodies outside the solar system can be divided into simple subject, conforming object, and diffusing object . Like Stevenson 2-18, the largest star in the universe we mentioned above, it belongs to the simple subject.
celestial object subdivision type diagram
Next If simple subjects are used as the main search object, then there is no celestial object with a diameter of more than 1 light year in the universe. Because the development of stars will be limited by many factors, the first is that when the stars enter the red giant stage, it means that life has entered the countdown.
Although it has a long time to expand and grow further at this time, it will eventually usher in its own death moment. When the time is right, the supernova will explode , and the expanding red giant will eventually become the extremely dense neutron star or black hole .
Spectacular supernova explosion
The second point is that there is a established boundary for the mass of stars, which people call it Eddington extreme , which was discovered by British astrophysicist Arthur Stanley Eddington , and is calculated from the equilibrium of gravity and radiation pressure.
The theory holds that when the mass of a star exceeds the Eddington limit, it will no longer continue to absorb matter.
However, in later detections, scientists discovered that many stars exceeded Eddington's limit. But we cannot judge it as an incorrect theory because judging by humans' current observation methods, it is actually not clear and accurate enough.
Eddington's limit points out that the mass of stars has an upper limit
Take shield UY, which once sat firmly on the largest star in the universe as an example. Many scientists think that this guy's real body is not that big, but just "fat". In other words, when humans were estimating its diameter, they also calculated the thick layer of gas cloud around them.
It can be seen from this that a simple subject in the universe cannot reach a light-year diameter. Even , the largest black hole SDSS J073739.96+384413.2, has a mass of more than 100 billion times that of the sun, and its diameter does not reach a light-year .
Because based on the formula of Schwarzsie radius , it will be found that the diameter of the black hole is about 1.1 trillion kilometers, which is still far behind compared to the approximate number of about 10 trillion kilometers per light year.
Schematic diagram of the structural diagram of a black hole, the diameter is within the horizon
Does this mean that there are no celestial bodies with a diameter of more than 1 light year in the universe?
If we open the pattern and combine it with the broad definition of celestial bodies, we will find that there are actually many behemoths in the universe. For example, the complex objects of celestial bodies include galaxy, star cluster, galaxy cluster , etc., and the extended objects also include various nebula .
The diameters of these guys are larger than the other. Take Milky Way as an example, its diameter is about .1 to 160,000 light-years . In addition, the diameter of the nebula like the Hubble Telescope and the Weber Telescope have been photographed one after another.
Of course, many people still think that "celestial bodies" should be independent individuals. Celestial bodies such as nebula and galaxy that are both complex and cohesive and relatively weak cannot be considered in it.
The ship base big nebula photographed by Weber telescope
So, if you rank the cosmic celestial bodies alone by simply individuals, what other red superstars are similar to Stevenson 2-18? Where are they all located?
What other huge stars are there in the universe?
is the first thing that failed with Stevenson in the 2-18 ring war, which is also located in shield .
is also a red super giant, and its brightness is also amazing. is about 340,000 times that of the sun and 10 million times that of the earth.
However, this is the result of further research and observation. Before that, the "measurement value" estimated by people was significantly greater than the current value.
Comparison between Stevenson 2-18 and UY of the Shield
followed by Cygnus NML, which is located in Cygnus , and the radius of is about 1650 times that of the sun, and is separated from the earth by 5500 light years. Around it, there are also a large number of interstellar gas clouds, which may hinder people's accurate measurement of their true size.
Finally, there are Cygnus RW, Sagittarius VX, Cygnus KY, etc. The distance between these behemoths in the universe and the earth is relatively far.
Size comparison diagram of star giants
However, being close is not a good thing. After all, the larger the volume and mass in the universe, the greater the gravity. In this way, the relatively safe solar system may be affected by gravity pull.
