In our galaxy. This is associated with huge distances in space and the complexity of observations with subsequent analysis of the data obtained. To date, scientists have managed to detect and register about 50 billion luminaries. A more advanced technique allows us to explore the distant corners of space and obtain new information about objects.
Estimation and search for supergiants in space
Modern astrophysics in the process of space exploration is constantly faced with a large number of questions. The reason for this is the gigantic size of the visible universe, about fourteen billion light years. Sometimes, when observing a star, it is quite difficult to estimate the distance to it. Therefore, before setting out on a journey in search of determining which is the largest star in our galaxy, it is necessary to understand the level of difficulty in observing space objects.
Previously, until the beginning of the twentieth century, it was believed that our galaxy is one. Visible other galaxies were classified as nebulae. But Edwin Hubble dealt a crushing blow to the ideas of the scientific world. He argued that there are a large number of galaxies, and ours is not the largest.
Space is incredibly huge
The distances to the nearest galaxies are enormous. reach hundreds of millions of years. It is quite problematic for astrophysicists to determine which is the largest star in our galaxy.
Therefore, it is even more difficult to talk about other galaxies with trillions of stars, at a distance of a hundred or more million light years. In the process of research, new objects are opened. The discovered stars are compared and the most unique and largest are determined.
Supergiant in the constellation Scutum
The name of the largest star in our galaxy is UY Scuti, a red supergiant. This is a variable which varies from 1700 to 2000 solar diameters.
Our brain is not capable of representing such quantities. Therefore, for a complete idea of what size is the largest star in the galaxy, it is necessary to compare with the values \u200b\u200bthat are understandable to us. Our solar system is suitable for comparison. The size of the star is so large that if it is placed in the place of our Sun, then the boundary of the supergiant will be in the orbit of Saturn.
And our planet and Mars will be inside the star. The distance to this "monster" of space is about 9600 light years.
The largest star in the galaxy - UY Shield - can only be conditionally considered a "king". The reasons are obvious. One of them is the huge cosmic distances and cosmic dust, which make it difficult to obtain accurate data. Another problem is directly related to the physical properties of supergiants. With a diameter 1700 times larger than our celestial body, the largest star in our galaxy is only 7-10 times as massive as it is. It turns out that the density of the supergiant is millions of times less than the air around us. Its density is comparable to the Earth's atmosphere at an altitude of about a hundred kilometers above sea level. Therefore, it is rather problematic to determine exactly where the boundaries of a star end and its “wind” begins.
At the moment, the largest star in our galaxy is at the end of its development cycle. It expanded (the same process will happen with our Sun at the end of evolution) and began to actively burn helium and a number of other elements heavier than hydrogen. After a few million years, the largest star in the galaxy - UY Scuti - will turn into a yellow supergiant. And in the future - into a bright blue variable, and possibly into a Wolf-Rayet star.
Along with the "king" - the supergiant UY Scuti - about ten stars with similar sizes can be noted. These include VY Canis Major, Cepheus A, NML Cygnus, WOH G64 VV and a number of others.
It is known that all the largest stars are short-lived and very unstable. Such stars can exist both for millions of years and for several millennia, ending their life cycle in the form of a supernova or a black hole.
The largest star in the galaxy: the search continues
Observing serious changes over the past twenty years, it is worth assuming that over time our understanding of the possible parameters of supergiants will differ from previously known ones. And it is quite possible that in the coming years another supergiant will be discovered, with a larger mass or size. And new discoveries will prompt scientists to revise previously accepted dogmas and definitions.
Today you will learn about the most unusual stars. It is estimated that there are about 100 billion galaxies in the universe and about 100 billion stars in each galaxy. Given so many stars, there must be strange ones among them. Many of the sparkling, burning balls of gas are quite similar to each other, but some stand out for their odd size, weight, and behavior. Using modern telescopes, scientists continue to study these stars to better understand them and the universe, but mysteries still remain. Curious about the strangest stars? Here are 25 of the most unusual stars in the universe.
25. UY Scuti
Considered a supergiant star, UY Scuti is large enough to swallow up our star, half of our neighboring planets, and virtually our entire solar system. Its radius is about 1700 times the radius of the Sun.
24. Star of Methuselah
Photo: commons.wikimedia.org
The star of Methuselah, also called HD 140283, really lives up to its name. Some believe it is 16 billion years old, which is a problem since the Big Bang only happened 13.8 billion years ago. Astronomers have tried to use better methods of age determination to better date the star, but still believe it to be at least 14 billion years old.
23. Thorn-Zhitkov object
Photo: Wikipedia Commons.com
Initially, the existence of this object was proposed theoretically by Kip Thorne (Kip Thorne) and Anna Zhitkova (Anna Zytkow), it represents two stars, a neutron and a red supergiant, combined into one star. A potential candidate for the role of this object has been named HV 2112.
22. R136a1 
Photo: flickr
Although UY Scuti is the largest star known to man, R136a1 is definitely one of the heaviest in the universe. Its mass is 265 times greater than the mass of our Sun. What makes her weird is that we don't know exactly how she was formed. The main theory is that it was formed by the merger of several stars.
21.PSR B1257+12
Photo: en.wikipedia.org
Most of the exoplanets in the solar system PSR B1257+12 are dead and bathed in deadly radiation from their old star. A surprising fact about their star is that the zombie star or pulsar has died, but the core still remains. The radiation emanating from it makes this solar system a no man's land.
20. SAO 206462
Photo: flickr
Consisting of two spiral arms spanning 14 million miles across, SAO 206462 is certainly the strangest and most unique star in the universe. While some galaxies are known to have arms, stars usually don't. Scientists believe that this star is in the process of creating planets.
19. 2MASS J0523-1403
Photo: Wikipedia Commons.com
2MASS J0523-1403 is arguably the smallest known star in the universe and is only 40 light years away. Due to its small size and mass, scientists believe that its age may be 12 trillion years.
18. Heavy metal subdwarfs
Photo: ommons.wikimedia.org
Astronomers recently discovered a pair of stars with a lot of lead in their atmospheres, which creates thick and heavy clouds around the star. They are called HE 2359-2844 and HE 1256-2738 and are located 800 and 1000 light years away respectively, but you can just call them heavy metal subdwarfs. Scientists are still not sure how they form.
17. RX J1856.5-3754
Photo: Wikipedia Commons.com
From the moment of their birth, neutron stars begin to ceaselessly lose energy and cool down. Thus, it is unusual that a 100,000-year-old neutron star such as RX J1856.5-3754 could be so hot and not show any signs of activity. Scientists believe that interstellar material is held together by the strong gravitational field of the star, resulting in enough energy to heat the star.
16. KIC 8462852
Photo: Wikipedia Commons.com
The star system KIC 8462852 has received a lot of attention and interest from SETI and astronomers for its unusual behavior of late. Sometimes it dims by 20 percent, which may mean that something is orbiting around it. Of course, this prompted some to conclude that these were aliens, but another explanation is the debris of a comet that entered the same orbit with a star.
15. Vega
Photo: Wikipedia Commons.com
Vega is the fifth brightest star in the night sky, but that doesn't make it weird at all. The high rotation speed of 960,600 km per hour gives it the shape of an egg, and not spherical, like our Sun. There are also temperature variations, with colder temperatures at the equator.
14.SGR 0418+5729
Photo: commons.wikimedia.org
A magnet located 6,500 light-years from Earth, SGR 0418+5729 has the strongest magnetic field in the universe. The strange thing about it is that it does not fit the image of traditional magnetars with a surface magnetic field, as in ordinary neutron stars.
13. Kepler-47
Photo: Wikipedia Commons.com
In the constellation Cygnus, 4,900 light-years from Earth, astronomers have first discovered a pair of planets orbiting two stars. Known as the Kelper-47 system, the orbiting stars outshine each other every 7.5 days. One star is roughly the size of our Sun, but only 84 percent as bright. The discovery proves that more than one planet can exist in a stressful orbit of a binary star system.
12. La Superba
Photo: commons.wikimedia.org
La Superba is another massive star located 800 light years away. It is about 3 times heavier than our Sun and four astronomical units in size. It is so bright that it can be seen from Earth with the naked eye.
11. MY Camelopardalis
Photo: commons.wikimedia.org
MY Camelopardalis was thought to be a single bright star, but the two stars were later found to be so close that they practically touch each other. Two stars slowly fuse together to form one star. No one knows when they will fully merge.
10.PSR J1719-1438b
Photo: Wikipedia Commons.com
Technically, PSR J1719-1438b is not a star, but it was once. When it was still a star, its outer layers were sucked out by another star, turning it into a small planet. What's even more amazing about this former star is that it's now a giant diamond planet five times the size of Earth.
9. OGLE TR-122b
Photo: Photo: commons.wikimedia.org
Usually, against the background of an average star, the rest of the planets resemble pebbles, but OGLE TR-122b is about the same size as Jupiter. That's right, it's the smallest star in the universe. Scientists believe it originated as a stellar dwarf billions of years ago, the first time a star comparable in size to a planet has been discovered.
8. L1448 IRS3B
Photo: commons.wikimedia.org
Astronomers discovered the three-star system L1448 IRS3B as it began to form. Using the ALMA telescope in Chile, they observed two young stars orbiting a much older star. They believe that these two young stars appeared as a result of a nuclear reaction with gas rotating around the star.
Photo: Wikipedia Commons.com
Mira, also known as Omicron Ceti, is 420 light-years away and is quite strange due to its constantly fluctuating brightness. Scientists consider it a dying star, located in the last years of its life. Even more amazing is that it travels through space at 130 kilometers per second and has a tail that spans several light-years.
6. Fomalhaut-C
Photo: Wikipedia Commons.com
If you think the two-star system was cool, then you might want to see Fomalhaut-C. It is a system with three stars only 25 light years from Earth. Although triple star systems are not entirely unique, this one is because the arrangement of the stars far away rather than close together is an anomaly. The star Fomalhaut-C is especially far away from A and B.
5. Swift J1644+57
Photo: Wikipedia Commons.com
The appetite of a black hole is not picky. In the case of Swift J1644+57, a dormant black hole woke up and engulfed the star. Scientists made this discovery in 2011 using X-ray and radio waves. It took 3.9 billion light years for light to reach Earth.
4.PSR J1841-0500
Photo: Wikipedia Commons.com
Known for their regular and constantly pulsating glow, they are rapidly rotating stars that rarely "turn off". But PSR J1841-0500 surprised scientists by only doing it for 580 days. Scientists believe that studying this star will help them understand how pulsars work.
3.PSR J1748-2446
Photo: Wikipedia Commons.com
The strangest thing about PSR J1748-2446 is that it is the fastest rotating object in the universe. It has a density 50 trillion times that of lead. To top it off, its magnetic field is a trillion times stronger than that of our Sun. In short, this is an insanely hyperactive star.
2. SDSS J090745.0+024507
Photo: Wikipedia Commons.com
SDSS J090745.0+024507 is a ridiculously long name for a runaway star. With the help of a supermassive black hole, the star has been blasted out of its orbit and is moving fast enough to exit the Milky Way. Let's hope that none of these stars will rush in our direction.
1. Magnetar SGR 1806-20
Photo: Wikipedia Commons.com
Magnetar SGR 1806-20 is a terrifying force that exists in our universe. Astronomers detected a bright flash at a distance of 50,000 light-years, and it was so powerful that it reflected off the Moon and illuminated the Earth's atmosphere for ten seconds. The solar flare raised questions among scientists about whether such a flare could lead to the extinction of all life on Earth.
The universe is a very big place and there is no way we can tell which star is the biggest. But what is the largest star known to us?
Before we get to the answer, let's look at our own Sun for scale. Our mighty star is 1.4 million km across. This is such a huge distance that it is difficult to put it on a scale. The sun makes up 99.9% of all matter in our solar system. In fact, there are one million Earth planets inside the Sun.
Astronomers use the terms "solar radius" and "solar mass" to compare larger and smaller stars, and we'll do the same. The solar radius is 690,000 km, one solar mass is 2 x 10 30 kilograms. This is 2,000,000,000,000,000,000,000,000,000,000 kg.
One huge known star in our galaxy is Eta Carinae, located 7500 light-years from the Sun and weighing 120 solar masses. It is a million times brighter than the sun. Most stars lose their mass over time, much like the solar wind. But Eta Carina is so big that every year it throws off a mass equal to 500 Earth masses. With so much mass lost, it is very difficult for astronomers to accurately measure where a star ends and its stellar wind begins.
Thus, the best answer from astronomers now is that the radius of Eta Carina is 250 times the size of the Sun.
And one interesting note: This Carina should explode soon, it will be one of the most spectacular supernovas that people have ever seen.
But the most massive star in the universe is R136a1, located in the Large Magellanic Cloud. There are disputes, but its mass may be more than 265 solar masses. And this is a mystery to astronomers, because theoretically the largest stars were considered to be about 150 solar masses, formed in the early universe when stars were formed from hydrogen and helium left over from the Big Bang. The answer to this controversy is that R136a1 may have been formed when several large stars merged together. Needless to say, R136a1 could explode into a hypernova any day now.
From the point of view of large stars, let's consider a familiar star located in the constellation of Orion - Betelgeuse. This red supergiant has a radius of 950 to 1200 times the size of the Sun, and would encompass the orbit of Jupiter if placed in our solar system.
But this is nothing. The largest known star is VY Canis Majoris. A red hypergiant in the constellation Canis Major, located about 5,000 light-years from Earth. Professor Robert Humphreys of the University of Minnesota recently calculated its upper size to be greater than 1,540 times the size of the Sun. If VY Canis Major were placed in our system, then its surface would extend beyond the orbit of Saturn.
It's the largest star we know of, but the Milky Way probably has dozens of stars that further obscure the clouds of gas and dust so we can't see them.
But let's see if we can answer the original question, what is the largest star in the universe? Obviously, it's virtually impossible for us to find it, the universe is a very big place, and there's no way we could peer into every corner.
The gun is another star, which is considered one of the largest.
According to theorists, the largest stars will be cold supergiants. For example, the temperature of VY Canis Majoris is only 3500 K. A really big star would be even colder. A cold supergiant with a temperature of 3000 K would be 2,600 solar in size.
Finally, here's a great video showing the size of various objects in space, from our tiny planet to VV Cepheus. VY Canis Majoris is not included in the animation, probably because they had no new information on this star.
Life on our entire planet depends on the Sun, and sometimes we do not realize that in fact there are many other galaxies in the Universe and within them. And our almighty Sun is just a small star among billions of other luminaries. Our article will tell you the name of the largest star in the world, which can still be covered by the human mind. Perhaps, beyond its borders, in hitherto unexplored worlds, there are even more gigantic stars of immense size ...
Measure stars in suns
Before talking about the name of the largest star, we clarify that the size of stars is usually measured in solar radii, its size is 696,392 kilometers. Many of the stars in our galaxy are larger than the Sun in many ways. Most of them belong to the class of red supergiants - large massive stars with a dense hot core and a sparse shell. Their temperature is noticeably lower than the temperature of blue and - 8000-30,000 K (on the Kelvin scale) and 2000-5000 K, respectively. Red stars are called cold, although in fact their temperature is slightly less than the maximum in the core of our Earth (6000 K).
Most celestial objects do not have constant parameters (including size), but rather are in constant change. Such stars are called variable - their sizes change regularly. This can happen for various reasons. Some variable stars are actually a system of several bodies exchanging masses, others are pulsating due to internal physical processes, shrinking and growing again.
What is the name of the largest star in the universe?
At a distance of 9.5 thousand light years from the Sun, it appeared on star maps at the end of the 17th century, thanks to the Polish astronomer Jan Hevelius. And two hundred years later, German astronomers from the Bonn Observatory added the star UY Shield (U-Ygrek) to the catalog. And already in our time, in 2012, it was found that UY Scuti is the largest of the known stars within the studied Universe.
The radius of the UY Scutum is about 1700 times greater than the radius of the Sun. This red hypergiant is a variable star, which means that its dimensions can reach even larger values. During periods of maximum expansion, the radius of the UY Shield is 1900 solar radii. The volume of this star can be compared with a sphere, the radius of which would be the distance from the center of the solar system to Jupiter.
Giants of Space: what are the names of the largest stars
In the neighboring galaxy, the Large Magellanic Cloud, is the second largest star within the studied space. Its name cannot be called particularly memorable - WOH G64, but you can take note that it is located in the constellation Dorado, a constant visible in the southern hemisphere. In size, it is slightly smaller than UY Scutum - about 1500 solar radii. But it has an interesting shape - the accumulation of a rarefied shell around the nucleus forms a spherical shape, but rather resembles a donut or bagel. Scientifically, this shape is called a torus.
According to another version, what is the name of the largest star after UY Shield, the leader is VY Canis Major. It is believed that its radius is equal to 1420 solar. But the surface of VY Canis Majoris is too rarefied - the Earth's atmosphere exceeds it in density by several thousand times. Due to the difficulty in determining what is the actual surface of the star, and what is already its accompanying shell, scientists still cannot come to a final conclusion regarding the size of VY Canis Major.
The heaviest stars
If we consider not the radius, but the mass of the celestial body, then the largest star is called as a set of letters and numbers in encryption - R136a1. It is also located in the Large Magellanic Cloud, but it belongs to the type of blue stars. Its mass corresponds to 315 solar masses. For comparison, the mass of the UY Shield is only 7-10 solar masses.
Another massive formation is called Eta Carinae, a double giant star in the 19th century, as a result of an outburst around this system, a nebula formed, named Homunculus because of its strange shape. The mass of Eta Carina is 150-250 solar masses.
The biggest stars in the night sky
The giant stars hiding in the depths of space are inaccessible to the eye of a simple layman - most often they can only be seen through a telescope. At night, in the starry sky, the brightest and closest objects to the Earth will seem large to us - be it stars or planets.
What is the name of the largest star in the sky and at the same time the brightest? This is Sirius, which is one of the closest stars to the Earth. In fact, it is not much larger than the Sun in size and mass - only one and a half to two times. But its brightness is really much greater - 22 times greater than that of the Sun.
Another bright and therefore seemingly large object in the night sky is actually not a star, but a planet. We are talking about Venus, the brightness of which in many respects exceeds the rest of the stars. Its brilliance is visible closer to sunrise or some time after sunset.
Seemingly inconspicuous UY Shield
Modern astrophysics in terms of stars seems to be re-experiencing its infancy. Observations of the stars give more questions than answers. Therefore, when asking which star is the largest in the Universe, you need to be immediately ready for answers. Are you asking about the largest star known to science, or about what limits science limits a star to? As is usually the case, in both cases you will not get a definitive answer. The most likely candidate for the largest star quite equally shares the palm with his "neighbors". As for how much it can be less than the real "king of the star" also remains open.
Comparison of the sizes of the Sun and the star UY Scuti. The sun is an almost invisible pixel to the left of UY Shield.
The supergiant UY Scutum, with some reservation, can be called the largest star observed today. Why "with reservation" will be said below. UY Scutum is 9500 light-years away and is seen as a dim variable star visible through a small telescope. According to astronomers, its radius exceeds 1700 radii of the Sun, and during the pulsation period this size can increase to as much as 2000.
It turns out that if such a star were placed in the place of the Sun, the current orbits of a terrestrial planet would be in the depths of a supergiant, and the boundaries of its photosphere would sometimes rest against the orbit. If we imagine our Earth as a grain of buckwheat, and the Sun as a watermelon, then the diameter of the UY Shield will be comparable to the height of the Ostankino TV tower.
To fly around such a star at the speed of light will take as much as 7-8 hours. Recall that the light emitted by the Sun reaches our planet in just 8 minutes. If you fly at the same speed with which it makes one revolution around the Earth in an hour and a half, then the flight around the UY Shield will last about 36 years. Now imagine these scales, given that the ISS flies 20 times faster than a bullet and tens of times faster than passenger airliners.
Mass and Luminosity of UY Shield
It is worth noting that such a monstrous size of the UY Shield is completely incomparable with its other parameters. This star is "only" 7-10 times more massive than the Sun. It turns out that the average density of this supergiant is almost a million times lower than the density of the air surrounding us! For comparison, the density of the Sun is one and a half times the density of water, and a grain of matter even “weighs” millions of tons. Roughly speaking, the averaged matter of such a star is similar in density to the layer of the atmosphere located at an altitude of about one hundred kilometers above sea level. This layer, also called the Karman line, is a conditional boundary between the earth's atmosphere and space. It turns out that the density of the UY Shield is only a little short of the vacuum of space!
Also UY Shield is not the brightest. With its own luminosity of 340,000 solar, it is ten times dimmer than the brightest stars. A good example is the star R136, which, being the most massive star known today (265 solar masses), is almost nine million times brighter than the Sun. At the same time, the star is only 36 times larger than the Sun. It turns out that R136 is 25 times brighter and about the same times more massive than UY Shield, despite the fact that it is 50 times smaller than the giant.
Physical parameters of the UY Shield
In general, UY Scuti is a pulsating variable red supergiant of spectral type M4Ia. That is, on the Hertzsprung-Russell spectrum-luminosity diagram, UY Scutum is located in the upper right corner.
At the moment, the star is approaching the final stages of its evolution. Like all supergiants, she began to actively burn helium and some other heavier elements. According to modern models, in a matter of millions of years, UY Scutum will gradually turn into a yellow supergiant, then into a bright blue variable or a Wolf-Rayet star. The final stages of its evolution will be a supernova explosion, during which the star will shed its shell, most likely leaving behind a neutron star.
Already now UY Scutum shows its activity in the form of semi-regular variability with an approximate pulsation period of 740 days. Given that a star can change its radius from 1700 to 2000 solar radii, the rate of its expansion and contraction is comparable to the speed of spaceships! Its mass loss is an impressive rate of 58 millionth solar masses per year (or 19 Earth masses per year). This is almost one and a half earth masses per month. So, being on the main sequence millions of years ago, UY Scutum could have had a mass of 25 to 40 solar masses.
Giants among the stars
Returning to the reservation mentioned above, we note that the primacy of UY Shield as the largest known star cannot be called unequivocal. The fact is that astronomers still cannot determine the distance to most stars with a sufficient degree of accuracy, and therefore estimate their size. In addition, large stars tend to be very unstable (recall the UY Scutum pulsation). Similarly, they have a rather blurry structure. They may have a rather extended atmosphere, opaque gas and dust shells, disks, or a large companion star (an example is VV Cephei, see below). It is impossible to say exactly where the boundary of such stars passes. In the end, the well-established concept of the boundary of stars as the radius of their photosphere is already extremely arbitrary.
Therefore, this number can include about a dozen stars, which include NML Cygnus, VV Cepheus A, VY Canis Major, WOH G64 and some others. All these stars are located in the vicinity of our galaxy (including its satellites) and are in many ways similar to each other. All of them are red supergiants or hypergiants (see below for the difference between super and hyper). Each of them in a matter of millions, or even thousands of years, will turn into a supernova. They are also similar in size, ranging from 1400-2000 solar.
Each of these stars has its own peculiarity. So in UY Shield, this feature is the previously discussed variability. WOH G64 has a toroidal gas and dust envelope. Extremely interesting is the double eclipsing variable star VV Cephei. It is a close system of two stars, consisting of the red hypergiant VV Cephei A and the blue main sequence star VV Cephei B. The centers of these stars are located from each other in some 17-34 . Considering that the VV radius of Cepheus B can reach 9 AU. (1900 solar radii), the stars are located at "arm's length" from each other. Their tandem is so close that whole pieces of the hypergiant flow with great speeds to the “little neighbor”, which is almost 200 times smaller than it.
Looking for a leader
Under such conditions, estimating the size of stars is already problematic. How can one talk about the size of a star if its atmosphere flows into another star, or smoothly passes into a gas and dust disk? This is despite the fact that the star itself consists of a very rarefied gas.
Moreover, all the largest stars are extremely unstable and short-lived. Such stars can live for a few millions, or even hundreds of thousands of years. Therefore, observing a giant star in another galaxy, you can be sure that a neutron star is now pulsating in its place or a black hole is bending space, surrounded by the remnants of a supernova explosion. If such a star is even thousands of light years away from us, one cannot be completely sure that it still exists or has remained the same giant.
Add to this the imperfection of modern methods for determining the distance to stars and a number of unspecified problems. It turns out that even among the ten largest known stars, it is impossible to single out a certain leader and arrange them in ascending order of size. In this case, Shield's UY was cited as the most likely candidate to lead the Big Ten. This does not mean at all that its leadership is undeniable and that, for example, NML Cygnus or VY Canis Major cannot be larger than her. Therefore, different sources can answer the question about the largest known star in different ways. This speaks rather not about their incompetence, but about the fact that science cannot give unambiguous answers even to such direct questions.
The largest in the universe
If science does not undertake to single out the largest among the discovered stars, how can we say which star is the largest in the Universe? According to scientists, the number of stars even within the boundaries of the observable universe is ten times greater than the number of grains of sand on all the beaches of the world. Of course, even the most powerful modern telescopes can see an unimaginably smaller part of them. The fact that the largest stars can be distinguished by their luminosity will not help in the search for a “stellar leader”. Whatever their brightness is, it will fade when observing distant galaxies. Moreover, as noted earlier, the brightest stars are not the largest (an example is R136).
Also remember that when observing a large star in a distant galaxy, we will actually see its "ghost". Therefore, it is not easy to find the largest star in the Universe, its searches will be simply meaningless.
Hypergiants
If the largest star is impossible to find practically, maybe it is worth developing it theoretically? That is, to find a certain limit, after which the existence of a star can no longer be a star. Even here, however, modern science faces a problem. The current theoretical model of the evolution and physics of stars does not explain much of what actually exists and is observed in telescopes. An example of this is the hypergiants.
Astronomers have repeatedly had to raise the bar for the limit of stellar mass. This limit was first introduced in 1924 by the English astrophysicist Arthur Eddington. Having obtained the cubic dependence of the luminosity of stars on their mass. Eddington realized that a star cannot accumulate mass indefinitely. The brightness increases faster than the mass, and sooner or later this will lead to a violation of hydrostatic equilibrium. The light pressure of the increasing brightness will literally blow away the outer layers of the star. The limit calculated by Eddington was 65 solar masses. Subsequently, astrophysicists refined his calculations by adding unaccounted components to them and using powerful computers. So the modern theoretical limit for the mass of stars is 150 solar masses. Now remember that the mass of R136a1 is 265 solar masses, which is almost twice the theoretical limit!
R136a1 is the most massive star known today. In addition to it, several more stars have significant masses, the number of which in our galaxy can be counted on the fingers. Such stars are called hypergiants. Note that R136a1 is much smaller than the stars that, it would seem, should be below it in class - for example, the supergiant UY Shield. This is because hypergiants are called not the largest, but the most massive stars. For such stars, a separate class was created on the spectrum-luminosity diagram (O), located above the class of supergiants (Ia). The exact initial bar for the mass of a hypergiant has not been established, but, as a rule, their mass exceeds 100 solar masses. None of the biggest stars of the "Big Ten" falls short of these limits.
Theoretical impasse
Modern science cannot explain the nature of the existence of stars whose mass exceeds 150 solar masses. This raises the question of how a theoretical limit to the size of stars can be determined if the radius of a star, unlike mass, is itself a vague concept.
Let's take into account the fact that it is not known exactly what the stars of the first generation were, and what they will be in the course of the further evolution of the Universe. Changes in the composition, metallicity of stars can lead to radical changes in their structure. Astrophysicists have only to comprehend the surprises that will be presented to them by further observations and theoretical research. It is quite possible that UY Shield may turn out to be a real crumb against the background of a hypothetical "king-star" that shines somewhere or will shine in the farthest corners of our Universe.
