One of the most popular ways of presenting information today is the compilation of ratings - finding out the tallest person in the world, the longest river, the oldest tree, etc. There are such ratings in the world of astronomy - the science of stars.
From school lessons, we know well that our Sun, which gives our planet warmth and light, is very small on the scale of the Universe. Stars of this type are called yellow dwarfs, and among the countless millions of stars, many much larger and more spectacular astronomical objects can be found.
"Stellar" life cycle
Before looking for the biggest star, let's remember how stars live and what stages they go through in their development cycle.
As you know, stars are formed from gigantic clouds of interstellar dust and gas, which gradually thicken, increase in mass and, under the influence of their own gravity, shrink more and more. The temperature inside the cluster gradually rises, and the diameter decreases.
The phase, indicating that the astronomical object has become a full-fledged star, lasts 7-8 billion years. Depending on the temperature, stars can be blue, yellow, red, etc. in this phase. The color is determined by the mass of the star and the physical and chemical processes taking place in it. 
But any star eventually begins to cool down and simultaneously expand in volume, turning into a "red giant", the diameter exceeding the original star by tens or even hundreds of times. At this time, the star can pulsate, expanding, then contracting in diameter.
This period lasts several hundred million years and ends with an explosion, after which the remnants of the star collapse, forming a faint "white dwarf", neutron star or "black hole".
So, if we are looking for the largest star in the Universe, then it is likely to be a "red giant" - a star in the aging phase.
The biggest star
To date, astronomers know a lot of "red giants", which can be called the largest stars in the observable part of the Universe. Since this type of stars is subject to pulsation, in different years the leaders in size were considered:
- KY Cygnus - the mass exceeds the mass of the Sun by 25 times, and the diameter is 1450 solar;
- VV Cepheus - with a diameter of about 1200 solar;
- VY Canis Major - considered the largest in our Galaxy, its diameter is about 1540 solar diameters;
- VX Sagittarius - the diameter at the maximum pulsation phase reaches 1520 solar;
- WOH G64 - a star from the nearest neighboring galaxy, the diameter of which reaches, according to various estimates, 1500-1700 solar; 
- RW Cephei - with a diameter of 1630 solar diameters;
- NML Cygnus - "red giant", in circumference exceeding 1650 diameters of the Sun;
- UV Shield - today it is considered the largest in the observable part of the Universe, with a diameter of about 1700 diameters of our Sun.
The heaviest star in the universe
Another star-champion should be mentioned, which is designated by astronomers as R136a1 and is located in one of the galaxies in the Large Magellanic Cloud. Its diameter is not yet very impressive, but its mass is 256 times the mass of our Sun. This star violates one of the main astrophysical theories, which states that the existence of stars with a mass of more than 150 solar masses is impossible due to the instability of internal processes.
By the way, in accordance with astronomical calculations, R136a1 has lost a fifth of its mass - initially this figure was within 310 solar masses. It is believed that the giant was formed as a result of the merger of several ordinary stars, so it is not stable and can explode at any moment, turning into a supernova.
Even today it is ten million times brighter than the Sun. If we move R136a1 to our galaxy, it will eclipse the Sun with the same brightness with which the Sun is now eclipsing the Moon.
The brightest stars in the sky
Of those stars that we can see with the naked eye in the sky, the blue giant Rigel (constellation Orion) and the red Deneb (constellation Cygnus) have. 
The third brightest is the red Betelgeuse, which together with Rigel makes up the famous Orion Belt.
Look up at the night sky and see that it is filled with stars. But with the naked eye, you can only see a microscopic fraction of them. There are up to 100 billion stars in a galaxy alone, and there are even more galaxies in the Universe. Astronomers believe that there are about 10 ^ 24 stars in the world. These powerful power plants come in a wide variety of colors and sizes - and next to many of them, our Sun looks like a crumb. But which star will be the real giant of the heavens? We should start by defining what we mean by a giant. Will it be the star with the largest radius, for example, or with the largest mass?
Galactic giants
The star with the largest radius is probably UY Shield, an alternating bright supergiant in the constellation of Shield. Located 9,500 light-years from Earth and composed of hydrogen, helium and other elements heavier, almost the composition of our Sun, this star in radius bypasses it 1708 (plus or minus 192) times.
The star's circumference is about 7.5 billion kilometers. You would have to fly an airplane for 950 years to fully fly around it - and even light would take six hours and 55 minutes. If we replace our Sun with this, its surface would be somewhere between the orbits of Jupiter and Saturn. Of course, the Earth would not exist then.
Considering its huge size and possible mass, 20-40 times higher than the solar one (2-8 × 10³¹kg), the UY of the Shield will have a density of 7 × 10⁻⁶ kg / m³. In other words, it is billions of times less than the density of water.
Basically, if you put this star in the largest water bath in the universe, it would theoretically float. A million times less dense than the Earth's atmosphere at room temperature, it would also hang in the air like a balloon - if, of course, you can find enough space for it.
But if these incredible facts have already managed to surprise you, we haven't even started yet. UY Shield is certainly a big star, but far from being a heavyweight. The king of the heavyweights is the star R136a1, located in the Large Magellanic Cloud, 165,000 light years away.
Massive attack
This star, a sphere of hydrogen, helium and elements, is heavier, not much larger than the Sun, 35 times larger than it in radius, but 265 times more massive than it - which is noteworthy, given that over 1.5 million years of its life it has already lost 55 solar masses.
The Wolf-Rayet type of stars is far from stable. They look like a blurry blue sphere with no clear surface, blowing out incredibly powerful stellar winds. Such winds move at a speed of 2,600 km / s - 65 times faster than the Juno probe, the fastest man-made object.
As a result, the star loses mass at a rate of 3.21 × 10¹⁸ kg / s, which is equivalent to terrestrial losses in 22 days.
Such space rock stars quickly burn out and die quickly. R136a1 emits nine million times more energy than our sun, and would appear 94,000 times brighter than the sun to our eyes if it were to take its place. In fact, it is the brightest star discovered.
its surface is over 53,000 degrees Celsius (), and such a star will live no more than two million years. Her death will mark a colossal supernova explosion that will not even leave a black hole behind.
Of course, next to such giants, our Sun looks insignificant, but, again, it will also grow as it ages. In about seven and a half billion years, it will reach its maximum size and become a red giant, expanding so much that the current orbit of the Earth will be inside the star.
And yet we found these stars by studying only a small fraction of the universe. What other miracles await us?
People tend to gaze into the sky, observing millions and millions of stars. We dream of distant worlds and paint ourselves images of brothers in mind. Each world is illuminated by its own "sun". Exploratory technology looks deep into space for 9 billion light years.
But even this is not enough to say with precision how many stars there are in space. At the current stage of the study, 50 billion are known. This number is steadily growing, as there is constant research, technology is being improved. People will learn about new giants and dwarfs in the world of space objects. Which of the stars is the largest in the Universe?
Dimensions of the Sun
Thinking about the dimensions of the stars, understand what to compare with, feel the scale. The dimensions of our Sun are impressive. Its diameter is 1.4 million km. This huge number is difficult to imagine. This will be helped by the fact that the mass of the Sun is 99.9% of the mass of all objects in the Solar System. Theoretically, a million planets could be located inside our star.
Using these numbers, astronomers have coined the terms "solar radius" and "solar mass", which are used to compare the size and mass of space objects. The sun has a radius of 690,000 km and weighs 2 billion kilograms. Compared to other stars, the Sun is a relatively small space object.
Former star champion
The stellar mass is constantly "losing weight" due to the "stellar wind". Thermonuclear processes, continuously shaking the universal luminaries, lead to the loss of hydrogen - "fuel" for reactions. Accordingly, the mass also decreases. Therefore, it is difficult for scientists to give exact figures regarding the parameters of such large and incandescent objects. Luminaries age and after a supernova explosion turn into a neutron star or black hole.
For decades, VY in the constellation Canis Major was recognized as the largest star. Not so long ago, the parameters were clarified, and the calculations of scientists showed that its radius is 1300-1540 solar radii. The giant is 2 billion kilometers in diameter and is located 5,000 light-years from Earth.
To imagine the size of this object, imagine that it will take 1200 years to fly around it, moving at a speed of 800 km / h. If you suddenly imagine that the Earth was compressed to 1 cm and VY was reduced in the same way, then the giant will be 2.2 km in size.
But the mass of the star is small and exceeds the mass of the Sun only 40 times. This is due to the low density of the substance. The brightness of the luminary is truly amazing. It emits light 500,000 times brighter than ours. VY was first mentioned in 1801. It was described by the scientist Joseph Jerome de Lalande. The entry says that the luminary belongs to the seventh class.
Since 1850, observations have indicated a gradual loss of brightness. The outer edge of VY began to increase because the forces of gravity no longer keep the mass at a constant level. Soon (by cosmic standards) the explosion of this supernova star is possible. Scientists say it could happen tomorrow or in a million years. Science has no exact figures.
Reigning Star Champion
Space exploration continues. In 2010, scientists led by Paul Crowter saw an impressive space object using the Hubble Telescope. While exploring the Large Magellanic Cloud, astronomers discovered a new star and named it R136a1. The distance from us to R136a1 is 163,000 light years.
The parameters shocked scientists. The giant's mass exceeds the mass of the Sun by 315 times, despite the fact that it was previously stated that there are no stars in space that exceed our Sun in mass by 150 times. Such a phenomenon occurred, according to the hypothesis of scientists, due to the combination of several objects. The brightness of the R136a1 glow exceeds the brightness of the radiation of our sun by 10 million times.
During the period from its discovery to our time, the star has lost one fifth of its mass, but it is still considered the record holder, even among its neighbors. They were also opened by Crowther's group. These objects also exceeded the limit of 150 solar masses.
Scientists have calculated that if R136a1 is placed in the solar system, then the brightness of the glow compared to our star will be the same as if the brightness of the Sun and the Moon were compared.
This is the largest star known to mankind so far. Surely in the Milky Way galaxy there are dozens, if not hundreds, of larger luminaries, closed from our eyes by gas and dust clouds.
VV Cephei 2... VV Cepheus 2 is located at 2,400 light years, which is 1600-1900 times the size of the Sun. The radius is 1050 times the radius of our Sun. In terms of light emission, the star exceeds the landmark from 275 to 575 thousand times. It is a variable pulsar that pulsates with an interval of 150 days. The speed of the cosmic wind directed away from the star is 25 km / sec.
Dimensions of the Sun and Star VV Cephei 2 Research has proven that VV Cephei 2 is a double star. The second star B is eclipsed regularly every 20 years. VV Cephei B revolves around the main star VV Cephei 2. It is blue, with a turnover period of 20 years. The eclipse lasts 3.6 years. The object is 10 times more massive than the Sun and 100,000 times more intense than the Sun.
Mu Cephei... In Cepheus, a red supergiant flaunts, 1650 times the size of the Sun. Mu Cephei is the brightest star in the Milky Way. The glow brightness is 38,000 times higher than the reference point. It is also known as Herschel's garnet star. Studying the star in the 1780s, the scientist called it "a delightfully beautiful garnet-colored object."
In the sky of the northern hemisphere, it is observed without a telescope from August to January, it resembles a drop of blood in the sky. After two to three million years, a giant supernova explosion is expected, which will turn the star into a black hole or a pulsar and a gas and dust cloud.
The red giant V838 in the constellation Monicorn shines 20,000 light-years from Earth. This cluster of stars, previously unknown to anyone, "became famous" in 2002. At this time, an explosion occurred there, which astronomers initially perceived as a supernova explosion. But due to its young age, the star did not approach the cosmic "demise".
For a long time they could not even guess what the cause of the cataclysm was. It is now hypothesized that the object has swallowed up a "companion star" or objects orbiting around it.
The object is credited with dimensions from 1170 to 1970 solar radii. Due to the gigantic distance, scientists do not give exact figures for the mass of the red variable star.
Until recently, scientists believed that the parameters of WHO 64 are comparable to R136a1 from the constellation Canis Major.
But it was found that the size of this star is only 1540 times larger than the sun. It shines from the Great Magellanic Cloud.
V354 Cephei... The red supergiant V354 Cephei, 9,000 light years from Earth, is invisible without a telescope.
It is located in the Milky Way galaxy. The temperature on the shell is 3650 degrees Kelvin, the radius is 1520 times greater than the sun and is determined at 1.06 billion km.
KY Swan... It would take 5000 light years to fly to KY Cygnus. This time is difficult to imagine. Such numbers mean that a ray of light flies at a hyperluminal speed from the star to the Earth for 5000 years.
If we compare the radius of the object and the Sun, then it will be 1420 solar radii. The mass of the star is only 25 times the mass of the landmark. But KY will quite compete for the title of the brightest star in the part of the Universe open to us. Its luminosity surpasses that of the Sun by a factor of millions.
KW Sagittarius... 10,000 irresistible light years separate us from the KW star in Sagittarius.
It is a red supergiant with a size of 1,460 solar radii and a luminosity 360,000 times that of our Sun.
The constellation is visible in the sky of the southern hemisphere. It is easy to find it on the surface of the Milky Way. The star cluster was first described by Ptolemy in the second century.
RW Cephei... The dimensions of the RW Cephei are still being argued about. Some scientists argue that the dimensions are equal to 1260 radii of the landmark, others are inclined that they are 1650 solar radii. It is the largest variable star.
If we move it to the place of the Sun in our system, then the supergiant's photosphere will be between the trajectories of Saturn and Jupiter. The star is rapidly flying towards the solar system at a speed of 56 km / sec. The end of the star will turn it into a supernova, or the core will collapse into a black hole.
Betelgeuse. The red giant Betelgeuse is located in Orion 640 light years away. The size of Betelgeuse is 1100 solar radii. Astronomers are confident that in the near future there will be a period of the star's degeneration into a black hole or supernova. Humanity will see this universal show from the "first row".
As we eagerly peer into the sky with all our instruments and explore it with robotic spaceships and missions with human crews, we will certainly make new amazing discoveries that will take us even further into the vastness of space.
We are constantly exploring new objects among trillions of celestial bodies. We will open more than one new star, which in size will outshine the already known ones. But alas, we will never know about the true scale of the Universe.
In fact, this question is not as simple as it seems. Determining the exact sizes of stars is very difficult, it is calculated based on a lot of indirect data, because we cannot see their disks directly. So far, direct observation of the stellar disk has been carried out only for a few large and close supergiants, and there are millions of stars in the sky. Therefore, it is not so easy to determine which is the largest star in the Universe - you have to rely mainly on the calculated data.
In addition, in some stars, the border between the surface and the huge atmosphere is very blurred, and where one ends and another begins is difficult to understand. But this is an error not for some hundreds, but for millions of kilometers.
Many stars do not have a strictly defined diameter, they pulsate, and become larger and smaller. And they can change their diameter very significantly.
Besides, science does not stand still. More and more accurate measurements are being made, distances and other parameters are being refined, and some stars are unexpectedly much more interesting than they seemed. This also applies to sizes. Therefore, we will consider several candidates that belong to the largest stars in the Universe. Note that they are all not very far away in cosmic terms, and they are also the largest stars in the Galaxy.
A red hypergiant that claims to be the largest star in the universe. Alas, this is not so, but very close. In terms of size, it is in third place.
VV Cepheus - that is, double, and the giant in this system is component A, and we will talk about it. The second component is an unremarkable blue star, 8 times the size of the Sun. But the red hypergiant is also a pulsating star, with a period of 150 days. Its dimensions can vary from 1050 to 1900 solar diameters, and at its maximum it shines 575,000 times brighter than our star!
This star is 5,000 light-years away from us, and at the same time in the sky it has a brightness of 5.18 m, that is, with a clear sky and good vision, it can be found, and even with binoculars it is generally easy.
UY Shield
This red hypergiant is also striking in its size. Some sites mention it as the largest star in the universe. It belongs to semi-regular variables and pulsates, so the diameter can vary - from 1708 to 1900 solar diameters. Just imagine a star 1900 times larger than our Sun! If you place it in the center of the solar system, then all the planets, up to Jupiter, will be inside it.
Sun, Sirius, Pollux, Arcturus, against the background of the UY Shield. It is probably the largest star in the universe.
In numbers, the diameter of this one of the largest stars in space is 2.4 billion kilometers, or 15.9 astronomical units. Inside it could fit 5 billion suns. It shines 340,000 times stronger than the Sun, although the surface temperature is much lower - due to its larger area.
At the peak of brightness UY of the Shield, it is visible as a faint reddish star with a brightness of 11.2 m, that is, it can be seen through a small telescope, but it is not visible to the naked eye. The fact is that the distance to this large star is 9500 light years - we would never see another on it. In addition, there are dust clouds between us - if they were not there, UY Shield would be one of the brightest stars in our sky, despite the great distance to it.
UY Shield is a huge star. She can be compared with the previous candidate - VV Cephei. At the maximum, they are about the same, and it is not even clear which one is greater. However, there is definitely an even bigger star!
VY Big Dog
The diameter of VY, however, according to some sources, is estimated at 1800-2100 solar, that is, it is a clear record among all other red hypergiants. If it were in the center of the solar system, it would swallow all the planets, along with Saturn. Previous candidates for the title of the largest stars in the Universe would also fit into it completely.
Light takes only 14.5 seconds to circle our Sun completely. The light would have to fly 8.5 hours to go around VY Big Dog! If you were to make such a flyby along the surface in a fighter jet, at a speed of 4500 km / h, such a non-stop journey would take 220 years.
Comparison of the sizes of the Sun and VY Canis Major.
This star still raises a lot of questions, since its exact size is difficult to establish due to the diffuse corona, which has a much lower density than the solar one. And the star itself has a density thousands of times less than the density of the air we breathe.
In addition, VY of Canis Major is losing its substance and has formed a noticeable nebula around itself. This nebula may now have even more matter than the star itself. In addition, it is unstable, and in the next 100 thousand years it will explode as a hypernova. Fortunately, it is 3900 light years away, and the Earth is not threatened by this terrible explosion.
This star can be found in the sky with binoculars or a small telescope - its brightness varies from 6.5 to 9.6 m.
What is the largest star in the universe?
We looked at some of the largest stars in the universe known to scientists today. Their sizes are amazing. All of them are candidates for this title, but the data is constantly changing - science does not stand still. According to some reports, UY Shield can also "swell" up to 2200 solar diameters, that is, it becomes even larger than VY Big Dog. On the other hand, there is too much controversy about the VY size of Canis Major. So these two stars are practically equal candidates for the title of the largest stars in the Universe.
Which of them turns out to be more in fact, will be shown by further research and clarifications. While the majority is inclined in favor of UY Shield, and you can safely call this star the largest in the Universe, it will be difficult to refute this statement.
Of course, talking about the entire Universe is not very correct. This is perhaps the largest star in our Milky Way galaxy known to scientists today. But since it has not yet been discovered yet larger, it is still the largest in the Universe.
In contact with
In our galaxy. This is associated with huge distances in space and the complexity of observations with the subsequent analysis of the data obtained. To date, scientists have managed to discover and register about 50 billion luminaries. More advanced technology allows you to explore distant corners of space and receive new information about objects.
Assessment 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, observing a star, it is quite difficult to estimate the distance to it. Therefore, before embarking on a journey in search of a definition of what is the largest star in our galaxy, it is necessary to understand the level of complexity of observing space objects.
Earlier, before 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 notions of the scientific world. He argued that there are many galaxies, and ours is not the largest.
The cosmos 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 one hundred and more million light years. In the process of research, new objects are discovered. The discovered stars are compared and the most unique and largest ones are determined.
Supergiant in the constellation of the Shield
The name of the largest star in our galaxy is UY Shield, a red supergiant. This is a variable which varies from 1700 to 2000 times the diameter of the Sun.
Our brains are incapable of imagining such quantities. Therefore, for a complete understanding of what size the largest star in the galaxy is, it is necessary to compare it with the values we understand. 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 border 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 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 more massive from it. It turns out that the density of the supergiant is millions of times less than the air around us. Its density is comparable to that of the Earth's atmosphere at an altitude of about one hundred kilometers above sea level. Therefore, it is quite problematic to determine exactly where the boundaries of the 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 occur with our Sun at the end of evolution) and began active combustion of helium and a number of other elements heavier than hydrogen. After a few million years, the largest star in the galaxy - UY Shield - will turn into a yellow supergiant. And later - into a bright blue variable, and possibly into a Wolf-Rayet star.
Along with the "king" - the UY Shield supergiant - 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.
All the largest stars are known to be short-lived and highly unstable. Such stars can exist for both millions of years and 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
Looking at the dramatic changes over the past twenty years, it is worthwhile to assume that over time, our understanding of the possible parameters of supergiants will differ from those previously known. And it is quite possible that in the coming years another supergiant will be discovered, with a greater mass or size. And new discoveries will push scientists to revise previously adopted dogmas and definitions.