Living our lives on the satellite of a small star on the outskirts of the Universe, we cannot even imagine its true scope. The size of the Sun seems incredible to us, and a larger star simply does not fit into our imagination. What can we say about monster stars - super and hyper giants next to which our Sun is no larger than a speck of dust.
| N | Star | Optimum | Score Limits |
| 1 | 2037 | 1530-2544 | |
| 2 | 1770 | 1540-2000 | |
| 3 | 1708 | 1516-1900 | |
| 4 | 1700 | 1050-1900 | |
| 5 | 1535 | ||
| 6 | 1520 | 850-1940 | |
| 7 | 1490 | 950-2030 | |
| 8 | 1420 | 1420-2850 | |
| 9 | 1420 | 1300-1540 | |
| 10 | 1411 | 1287-1535 | |
| 11 | 1260 | 650-1420 | |
| 12 | 1240 | 916-1240 | |
| 13 | 1230 | 780-1230 | |
| 14 | 1205 | 690-1520 | |
| 15 | 1190 | 1190-1340 | |
| 16 | 1183 | 1183-2775 | |
| 17 | 1140 | 856-1553 | |
| 18 | 1090 | ||
| 19 | 1070 | 1070-1500 | |
| 20 | 1060 | ||
| 21 | 1009 | 1009-1460 |
The star is located in the Altar Constellation, being the largest cosmic object in it. It was discovered by the Swedish astronomer Västerlund, after whom it was named in 1961.
Westerland 1-26 has a mass 35 times greater than the Sun. A brightness of 400,000. However, it is impossible to see the star with the naked eye due to its enormous distance from our planet, amounting to 13,500,000 light years. If you place Westerland in our solar system, its outer shell will engulf the orbit of Jupiter.
Giant from the Large Magellanic Cloud. The size of the star is almost 3 billion kilometers (1540 - 2000 solar radii), the distance to WOH G64 is 163 thousand light years. years.
The star has long been considered the largest, but recent studies have shown that its radius has decreased significantly, and according to some estimates for 2009, it was 1540 times the size of our star. Scientists suspect that a strong stellar wind is to blame.
UY Shield
In the Milky Way Constellation, and in the entire Universe known to mankind, this is the brightest and one of the largest stars. The distance of this red supergiant from Earth is 9,600 light years. The diameter changes quite actively (at least according to observations from Earth), so we can talk about an average of 1708 solar diameters.
The star belongs to the category of red supergiants, its luminosity exceeds that of the Sun by 120,000 times. The cosmic dust and gas that have accumulated around the star over the billions of years of its existence significantly reduce the luminosity of the star, so it is impossible to determine it more accurately.
Jupiter would be completely engulfed along with its orbit if the Sun were the size of UY Scuti. Oddly enough, for all its greatness, the star is only 10 times more massive than our star.
The star belongs to the class of binaries and is 5000 light years away from Earth. It is approximately 1700 times larger than our Sun in linear dimensions. VV Cephei A is considered one of the largest studied stars in our Galaxy.
The history of observations of it dates back to 1937. It was studied mainly by Russian astronomers. The studies revealed that the star darkens periodically once every 20 Earth years. In our Galaxy, it is considered one of the brightest stars. The mass of VV Cepheus A is approximately 80-100 times greater than that of the Sun.
The radius of the space object is 1535 times greater than the solar one, its mass is approximately 50. The brightness index of RW Cepheus is 650,000 times higher than that of the Sun. The surface temperature of the celestial object ranges from 3500 to 4200 K, depending on the intensity of thermonuclear reactions in the bowels of the star.
An extremely bright variable hypergiant from the constellation Sagittarius. VX Sagittarius pulsates in long irregular periods. This is the most studied supergiant star, its radius is 850 - 1940 solar and tends to decrease.
The distance from Earth to this yellow supergiant is 12,000 light years. The mass is equal to 39 solar masses (despite the fact that the mass of the star itself is 45 times greater than the mass of the Sun). The dimensions of V766 Centauri are amazing; it is 1490 times larger in diameter than our Sun.
The yellow giant is located in a system of two stars, representing a part of them. The location of the second star of this system is such that it touches V766 Centauri with its outer shell. The described object has a luminosity that is 1,000,000 times greater than that of the Sun.
According to some sources, the largest star known universe, its radius, according to some calculations, can reach 2850 solar. But more often it is accepted as 1420.
Mass VY Canis Major exceeds the mass of the Sun by 17 times. The star was discovered at the beginning of the century before last. Later studies added information about all its main characteristics. The size of the star is so large that its flight around the equator takes eight light years.
The red giant is located in the constellation Canis Major. According to the latest scientific data, within the next 100 years the star will explode and turn into a supernova. The distance from our planet is approximately 4,500 light years, which in itself eliminates any danger from the explosion for humanity.
The diameter of this star, which belongs to the category of red supergiants, is approximately 1411 times the diameter of the Sun. The distance of AH Scorpius from our planet is 8900 light years.
The star is surrounded by a dense shell of dust, a fact confirmed by numerous photographs taken through telescopic observation. The processes occurring in the bowels of the star cause the variability of the star’s brightness.
The mass of AH Scorpius is equal to 16 solar masses, its diameter is 1200 times greater than that of the Sun. The maximum surface temperature is assumed to be 10,000 K, but this value is not fixed and can change in one direction or the other.
This star is also known as "Herschel's garnet star" after the astronomer who discovered it. It is located in the constellation of the same name Cepheus, is triple, and is located at a distance of 5600 light years from the Earth.
The main star of the system, MU Cephei A, is a red supergiant, the radius of which is different estimates, exceeds solar energy by 1300-1650 times. The mass of MU Cephei is 30 times greater than the Sun, the temperature at the surface is from 2000 to 2500 K. The luminosity of MU Cephei exceeds the Sun by more than 360,000 times.
This red supergiant belongs to the category of variable objects, located in the constellation Cygnus. The approximate distance from the Sun is 5500 light years.
The radius of BI Cygni is approximately 916-1240 solar radii. It has a mass 20 times greater than our star and a luminosity of 25,0000 times. The temperature of the upper layer of this space object is from 3500 to 3800 K. According to recent studies, the temperature on the surface of the star varies greatly due to intense thermonuclear reactions of the interior. During the period of greatest bursts of thermonuclear activity, the surface temperature can reach 5500 K.
A supergiant discovered in 1872, which becomes a hypergiant during maximum pulsation. The distance to S Perseus is 2420 parsecs, the pulsation radius is from 780 to 1230 r.s.
This red supergiant belongs to the category of irregular, variable objects with unpredictable pulsations. Located in the constellation Cepheus, 10,500 light years away. It is 45 times more massive than the Sun, its radius is 1500 times that of the Sun, which in digital terms is approximately 1,100,000,000 kilometers.
If we conditionally place V354 Cepheus in the center solar system, Saturn would be inside its surface.
This red giant is also a variable star. A semi-regular, fairly bright object is located about 9600 light years from our planet.
The radius of the star is within 1190-1940 solar radii. The mass is 30 times greater. The surface temperature of the object is 3700 K, the luminosity index of the star exceeds that of the Sun by 250,000 - 280,000 times.
The largest known star. At a temperature of 2300 K, its radius increases to 2775 solar, which is almost a third greater than any star known to us.
In the normal state, this figure is 1183.
Located space object in the constellation Cygnus, belongs to the red variable supergiants. The average distance from our planet, according to astronomers, is from 4600 to 5800 light years. The estimated radius of the celestial object ranges from 856 to 1553 solar radii. This range of indicators is caused by different levels of pulsation of the star in different periods of time.
The mass of BC Cygnus is from 18 to 22 solar mass units. The surface temperature is from 2900 to 3700 K, the luminosity value is approximately 150,000 times higher than the sun.
This well-studied supergiant, classified as a variable star, is located in the Carina Nebula. The approximate distance of the space object from the Sun is 8500 light years.
Estimates of the red giant's radius vary significantly, ranging from 1090 times the radius of our star. The mass is 16 times greater than the mass of the Sun, the surface temperature is 3700-3900 K. The average luminosity of a star is from 130,000 to 190,000 solar.
This red giant is located in the constellation Centaurus, its distance from our planet, according to various estimates, is from 8,500 to 10,000 light years. To date, the object has been studied relatively little, and there is little information about it. It is only known that the radius of V396 Centauri exceeds that of the Sun by approximately 1070 times. Presumably the temperature on the surface of the star is also estimated. According to rough estimates, it is in the range of 3800 – 45,000 K.
CK Carinae belongs to the so-called “variable” stellar objects, located in the constellation Carinae, at a distance of approximately 7500 light years from our planet. Its radius is 1060 times greater than the Sun. Astronomers have calculated that if this object were located at the center of the solar system, the planet Mars would be on its surface.
The star has a mass exceeding the mass of the Sun by about 25 times. Luminosity – 170,000 Suns, surface temperature at 3550 K.
The star is a red supergiant whose mass is from 10 to 20 solar masses. Located in the constellation Sagittarius, distance celestial body from our planet is 20,000 light years. The radius, according to maximum estimates, is approximately 1460 solar.
Its luminosity is 250,000 times greater than that of the sun. Surface temperature is from 3500 to 4000 K.
People tend to look up at the sky, observing millions and millions of stars. We dream of distant worlds and imagine images of brothers in mind. Each world is illuminated by its own “sun”. Research technology looks 9 billion light years deep into space.
But this is not enough to say with accuracy how many stars there are in space. At the current stage of study, 50 billion are known. This number is growing steadily as research continues and technology improves. People learn about new giants and dwarfs in the world of space objects. Which star is the largest in the Universe?
Dimensions of the Sun
When discussing the dimensions of stars, understand what to compare with, feel the scale. The size of our Sun is 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 makes up 99.9% of the mass of all objects in the Solar System. Theoretically, a million planets could fit inside our star.
Using these numbers, astronomers coined the terms “solar radius” and “solar mass,” which are used to compare the sizes and masses of cosmic objects. The radius of the Sun is 690,000 km and its weight is 2 billion kilograms. Compared to other stars, the Sun is a relatively small space object.
Former All-Star Champion
Stellar mass is constantly “losing” due to the “stellar wind”. Thermonuclear processes that continuously shake the universal stars lead to the loss of hydrogen - the “fuel” for reactions. Accordingly, the mass decreases. Therefore, it is difficult for scientists to give exact figures regarding the parameters of such large and hot objects. The luminaries age and after a supernova explosion they turn into a neutron star or a black hole.
For decades, VY was recognized as the largest star in the constellation Canis Major. Not so long ago, the parameters were clarified, and calculations by scientists showed that its radius is 1300-1540 solar radii. The diameter of the giant is 2 billion kilometers, and it is located 5000 light years from Earth.
To imagine the dimensions of this object, imagine that it would take 1,200 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 also reduced, 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 occurs due to the low density of the substance. The brightness of the luminary is truly surprising. 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 record says that the luminary belongs to the seventh class.
Since 1850, observations indicate a gradual loss of brightness. The outer edge of VY began to increase because gravitational forces no longer hold the mass at a constant level. Soon (by cosmic standards) this star may explode as a supernova. Scientists say this could happen tomorrow or in a million years. Science does not have exact figures.
Current Star Champion
Space exploration continues. In 2010, scientists led by Paul Crowther saw an impressive space object using Hubble telescope. While exploring the Large Magellanic Cloud, astronomers discovered a new star and gave it the name R136a1. The distance from us to R136a1 is 163,000 light years.
The parameters shocked scientists. The mass of the giant 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. This phenomenon occurred, according to scientists’ hypothesis, due to the combination of several objects. The brightness of R136a1 exceeds the brightness 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 is still considered a record holder even among its neighbors. They were also discovered by Crowther's group. These objects also exceeded the threshold 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. Surely in the Milky Way galaxy there are dozens, if not hundreds, of larger luminaries, hidden from our eyes by gas and dust clouds.
VV Cephei 2. Located 2400 light years away is VV Cephei 2, which is 1600-1900 times larger than the Sun. The radius is 1050 radii of our Sun. In terms of light emission, the star exceeds the benchmark from 275 to 575 thousand times. This is a variable pulsar, pulsating at intervals 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 eclipse of the second star B occurs regularly every 20 years. VV Cephei B orbits the main star VV Cephei 2. It is blue and has an orbital period of 20 years. The eclipse lasts 3.6 years. The object is 10 times larger than the Sun in mass and 100,000 times more luminous in intensity.
Mu Cephei. Cepheus is home to a red supergiant, 1650 times larger than the Sun. Mu Cephei is the brightest star in the Milky Way. The brightness of the glow is 38,000 times higher than the guideline. It is also known as “Herschel’s garnet star.” Studying the star in the 1780s, the scientist called it "a delightfully beautiful object of garnet color."
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 pulsar and a cloud of gas and dust.
About 20,000 light-years from Earth, the red giant V838 shines in the constellation Monoceros. 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 its cosmic “death.”
For a long time they could not even guess what the cause of the cataclysm was. It is now hypothesized that the object absorbed a “companion star” or objects orbiting around it.
The object is attributed 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 Large Magellanic Cloud.
V354 Cephei. Red supergiant V354 Cephei, located 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 solar radius and is determined to be 1.06 billion km.
KY Swan. It would take 5,000 light years to fly to KY Cygni. This time is hard to imagine. Such figures mean that a beam of light travels at hyperluminal speed from a star to Earth for 5,000 years.
If we compare the radius of the object and the Sun, 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 that is open to us. Its luminosity surpasses that of the sun by millions of times.
KW Sagittarius. 10,000 insurmountable light years separate us from the star KW in Sagittarius.
It is a red supergiant with a size of 1,460 solar radii and a luminosity 360,000 times greater than that of our Sun.
The constellation is visible in the sky of the southern hemisphere. It is easy to find on the surface of the Milky Way. The star cluster was first described by Ptolemy in the second century.
RW Cepheus. The dimensions of RW Cepheus are still being debated. Some scientists claim that the dimensions are equal to 1260 radii of the landmark, others are inclined to believe that they are 1650 solar radii. This is the largest variable star.
If it is moved to the place of the Sun in our system, then the photosphere of the supergiant 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 640 light years away in Orion. The size of Betelgeuse is 1100 solar radii. Astronomers are confident that in the near future there will be a period of degeneration of the star into a black hole or supernova. Humanity will see this universal show from the “front row”.
As we peer greedily into the sky with all our instruments and explore it with robotic spacecraft and human-crewed missions, we are sure to make amazing new 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 discover more than one new star, which will outshine the already known ones in size. But alas, we will never know about the true scale of the Universe.
Astronomers never cease to delight us with new discoveries, finding more and more stars in the Universe. Some of them can be seen at night with the naked eye, simply by looking into the night sky. Seeing others requires the most powerful telescopes. What is the biggest star in the universe? Where is it located and how is it different from its neighbors? We invite you to familiarize yourself with the rating of the largest stars that have already been discovered by astronomers in the universe.
AH Scorpio
This is a real red giant, which is located in the region of the constellation Scorpio at a distance of 12 thousand light years relative to our planet. Its radius exceeds the radius of the Sun by 1.5 thousand times.
KY Swan
To reach this star, which is located in the constellation Cygnus, it will take as much as 5 thousand light years to fly from Earth. Comparing the radius of the planet with the Sun, we can say that its radius is 1420 solar radii. But the planet’s mass is not so large - it is only 25 times heavier than our star. It could illuminate much more than the Sun, since the brightness of KY Cygnus exceeds the solar brightness many millions of times, so it may well win in the “Brightest” category.
VV Cephei A
This double is located in the constellation of the same name, the distance to which is about 5000 light years. It is recognized as one of the largest in its galaxy, second only to VY Canis Majoris. Estimating the radius at the equator of this star, we can say that it is equal to 1900 equatorial radii of our star.
VY Canis Majoris
If we consider the Milky Way, then it was this star that became its record holder, with a radius greater than the size of the Sun by more than 1540 times. According to astronomers' research, this star is very unstable and there is an assumption that over the next 100,000 years it will certainly explode, resulting in a gamma-ray burst that can destroy all life that is within 1-2 light years. As for planet Earth, it can only be saved by the enormous distance from our planet to VY Canis Majoris, which is about 4000 light years. Therefore, earthlings can be calm.
VX Sagittarius
Scientists note the pulsation of this variable star, as research has proven periodic change its temperature and volume. And its pulsation can be compared to the beating of a human heart. The equatorial radius of VX Sagittarius is 1520 solar. The star is located in the constellation of the same name, from which it received its name.
Westerland 1-26
The numerical value of the radius of this giant exceeds the Solar one by 1540 times. From Earth to Westerland 1-26 is about 11,500 light years.
WOH G64
The star WOH G64 is called a red star. It can be found by exploring the constellation Doradus, which is located in a galaxy called the Large Magellanic Cloud. Our solar system is about 163 thousand light years away. Its radius is 1730 times greater than that of the Sun. According to research, the star will cease to exist by becoming a supernova. However, this will not happen earlier than in 10-20 thousand years. Although during this time a lot of things can still change.
RW Cepheus
This giant star is red in color and is located more than 2,700 light years from Earth. Its radius at the equator is 1636 times greater than the radius of the Sun.
NML Swan
The star acquired its name based on the name of the constellation where it was discovered by astronomers. Its radius is 1650 times greater than the solar radius. A distance of 5300 light years separates us from NML Cygnus. While studying the structure of the planet, scientists discovered sulfur oxide, hydrogen sulfide and other substances in it.
UY Shield
Scientists agree that UY Scuti is the largest in the entire universe. The record holder is located in the constellation of the same name at a distance of approximately 9.5 thousand light years from us. The star is very bright, but this is hampered by the huge amount of dust and gas around the planet.
Stars are huge balls of hot plasma. The size of some of them will amaze even the most unimpressive reader. So, are you ready to be surprised?
Below is a list of the ten largest (in diameter) stars in the Universe. Let’s immediately make a reservation that this ten is made up of those stars that we already know. WITH high degree It is likely that in the vastness of our vast Universe there exist luminaries with an even larger diameter. It is also worth noting that some of the presented celestial bodies belong to the class of variable stars, i.e. they periodically expand and contract. And finally, we emphasize that in astronomy all measurements have some error, so the figures given here may differ to an insignificant degree for such a scale from the actual sizes of stars.
1. VY Canis Majoris
This red hypergiant has left all its competitors far behind. The radius of the star, according to various estimates, exceeds the solar one by 1800-2100 times. If VY Canis Majoris were the center of our Solar System, its edge would be very close to the orbit. This star is located about 4.9 thousand light years in the constellation Canis Major.
2. VV Cephei A
The star is located in the constellation Cepheus at a distance of about 2.4 thousand light years. This red hypergiant is 1600-1900 times larger than ours.
3. Mu Cephei
Located in the same constellation. This red supergiant is 1650 times larger than the Sun. In addition, Mu Cephei is one of the brightest stars. It is more than 38,000 times brighter than our star.
4. V838 Unicorn
This red variable star is located in the constellation Monoceros at a distance of 20 thousand light years from Earth. Perhaps it shone even more than VV Cephei A and Mu Cephei, but the huge distance separating the star from our planet does not allow at the moment make more accurate calculations. Therefore, it is usually assigned from 1170 to 1970 solar radii.
5. WHO G64
It was previously thought that this red hypergiant could rival VY Canis Majoris in size. However, it was recently discovered that this star from the constellation Doradus is only 1540 times larger than the Sun. The star is located outside the Milky Way in the dwarf galaxy Large Magellanic Cloud.
6. V354 Cephei
This red hypergiant is quite a bit smaller than WHO G64: it is 1520 times larger than the Sun. The star is relatively close, only 9 thousand light years from Earth in the constellation Cepheus.
7. KY Swan
This star is at least 1420 times larger than the Sun. But, according to some calculations, it could even top the list: the argument is serious - 2850 solar radii. However, the actual dimensions of the celestial body are most likely close to the lower limit, which brought the star to seventh place in our rating. The luminary is located 5 thousand light years from Earth in the constellation Cygnus.
8. KW Sagittarius
Located in the constellation Sagittarius, the red supergiant is 1460 times the radius of the Sun.
9. RW Cepheus
There is still controversy over the dimensions of the fourth representative of the Cepheus constellation. Its dimensions are about 1260-1650 solar radii.
10. Betelgeuse
This red supergiant is located just 640 light-years from our planet in the constellation Orion. Its size is 1180 solar radii. Scientists believe that Betelgeuse can be reborn at any moment, and we will be able to observe this interesting process almost “from the front row.”
The comparative sizes of stars can be estimated from this video:
The seemingly inconspicuous UY Shield
Modern astrophysics, in terms of stars, seems to be reliving its infancy. Star observations provide more questions than answers. Therefore, when asking which star is the largest in the Universe, you need to be immediately prepared for answering questions. Are you asking about the largest star known to science, or about what limits science limits a star? As is usually the case, in both cases you will not get a clear answer. The most likely candidate for the biggest star quite equally shares the palm with its “neighbors.” How much smaller it may be 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 Scutum.
With some reservations, the supergiant UY Scuti can be called the largest star observed today. Why “with reservation” will be stated below. UY Scuti is 9,500 light-years away from us and is observed as a faint variable star, visible in a small telescope. According to astronomers, its radius exceeds 1,700 solar radii, and during the pulsation period this size can increase to as much as 2,000.
It turns out, place such a star in the place of the Sun, the current orbits of the planet terrestrial group would find themselves in the depths of a supergiant, and the boundaries of its photosphere would at times abut 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 it will take as much as 7-8 hours. Let us remember that the light emitted by the Sun reaches our planet in just 8 minutes. If you fly at the same speed as it makes one revolution around the Earth in an hour and a half, then the flight around UY Scuti will last about 36 years. Now let’s imagine these scales, taking into account that the ISS flies 20 times faster than a bullet and tens of times faster than passenger airliners.
Mass and luminosity of UY Scuti
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 around us! For comparison, the density of the Sun is one and a half times higher than 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 a layer of atmosphere located at an altitude of about one hundred kilometers above sea level. This layer, also called the Karman line, is the conventional boundary between the earth's atmosphere and space. It turns out that the density of the UY Shield is only slightly short of the vacuum of space!
Also UY Scutum is not the brightest. With its own luminosity of 340,000 solar, it is tens of times dimmer than the brightest stars. A good example is the star R136, which, being the most massive of the currently known stars (265 solar masses), is almost nine million times brighter than the Sun. Moreover, the star is only 36 times larger than the Sun. It turns out that R136 is 25 times brighter and about the same number of times more massive than UY Scuti, despite the fact that it is 50 times smaller than the giant.
Physical parameters of UY Shield
Overall, UY Scuti is a pulsating variable red supergiant of spectral class M4Ia. That is, on the Hertzsprung-Russell spectrum-luminosity diagram, UY Scuti is located in the upper right corner.
At the moment, the star is approaching the final stages of its evolution. Like all supergiants, it began actively burning helium and some other heavier elements. According to modern models, in a matter of millions of years, UY Scuti will successively transform into a yellow supergiant, then into a bright blue variable or 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 Scuti is showing its activity in the form of semi-regular variability with an approximate pulsation period of 740 days. Considering that a star can change its radius from 1700 to 2000 solar radii, the speed of its expansion and contraction is comparable to the speed spaceships! Its mass loss is at an impressive rate of 58 million solar masses per year (or 19 Earth masses per year). This is almost one and a half Earth masses per month. Thus, being on the main sequence millions of years ago, UY Scuti could have had a mass of 25 to 40 solar masses.
Giants among the stars
Returning to the disclaimer stated above, we note that the primacy of the UY Shield as the largest of famous stars cannot be called unambiguous. The fact is that astronomers still cannot determine the distance to most stars with a sufficient degree of accuracy, and therefore estimate their sizes. In addition, large stars are usually very unstable (remember the pulsation of UY Scuti). Likewise, they have a rather blurred structure. They may have a fairly extensive atmosphere, opaque shells of gas and dust, disks, or a large companion star (for example, VV Cephei, see below). It is impossible to say exactly where the boundary of such stars lies. After all, the 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 Cephei A, VY Canis Majoris, 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 will turn into a supernova in a few millions, or even thousands of years. They are also similar in size, lying in the range of 1400-2000 solar.
Each of these stars has its own peculiarity. So in UY Scutum this feature is the previously mentioned variability. WOH G64 has a toroidal gas-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 centra of these stars are located from each other at some 17-34 . Considering that the radius of VV 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 at enormous speeds onto 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 we talk about the size of a star if its atmosphere flows into another star, or smoothly turns into a disk of gas and dust? This is despite the fact that the star itself consists of 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, when observing a giant star in another galaxy, you can be sure that it is now pulsating in its place. neutron star or space is bent by a black hole surrounded by the remnants of a supernova explosion. Even if such a star is thousands of light years away from us, one cannot be completely sure that it still exists or remains the same giant.
Let's add to this imperfection modern methods determining the distance to the stars and a number of unspecified problems. It turns out that even among a dozen famous biggest stars It is impossible to single out a specific leader and arrange them in ascending order of size. In this case, UY Shield was cited as the most likely candidate to lead the Big Ten. This does not mean at all that his leadership is undeniable and that, for example, NML Cygnus or VY Canis Majoris cannot be greater than her. That's why different sources the question of the largest known star can be answered differently. This speaks less of their incompetence than of the fact that science cannot give unambiguous answers even to such direct questions.
Largest in the Universe
If science does not undertake to single out the largest among the discovered stars, how can we talk about which star is the largest in the Universe? Scientists estimate that the number of stars, even within 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 portion of them. It will not help in the search for a “stellar leader” that the largest stars can stand out for their luminosity. Whatever their brightness, it will fade when observing distant galaxies. Moreover, as noted earlier, the most bright stars are not the largest (example - R136).
Let us 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; searching for it will simply be pointless.
Hypergiants
If the largest star is practically impossible to find, maybe it’s worth developing it theoretically? That is, to find a certain limit after which the existence of a star can no longer be a star. However, even here modern science faces a problem. The modern theoretical model of evolution and physics of stars does not explain much of what actually exists and is observed in telescopes. An example of this is 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 a 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 this will sooner or later lead to a violation of hydrostatic equilibrium. The light pressure of 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 and using powerful computers. So the current theoretical limit for the mass of stars is 150 solar masses. Now remember that R136a1 has a mass of 265 solar masses, which is almost twice the theoretical limit!
R136a1 is the most massive star currently known. In addition to it, several other stars have significant masses, the number of which in our galaxy can be counted on one hand. Such stars were called hypergiants. Note that R136a1 is significantly smaller than stars that, it would seem, should be lower in class - for example, the supergiant UY Scuti. This is because it is not the largest stars that are called hypergiants, but the most massive ones. For such stars, a separate class was created on the spectrum-luminosity diagram (O), located above the class of supergiants (Ia). The exact initial mass of a hypergiant has not been established, but, as a rule, their mass exceeds 100 solar masses. None of the Big Ten's biggest stars measure up to those limits.
Theoretical dead end
Modern science cannot explain the nature of the existence of stars whose mass exceeds 150 solar masses. This raises the question of how one can determine the theoretical limit on the size of stars if the radius of a star, unlike mass, is itself a vague concept.
Let us take into account the fact that it is not known exactly what the stars of the first generation were like, and what they will be like during the further evolution of the Universe. Changes in the composition and metallicity of stars can lead to radical changes in their structure. Astrophysicists have yet to comprehend the surprises that further observations and theoretical research will present to them. It is quite possible that UY Scuti 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.
