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 Scuti 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 television 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. Considering 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.

The closest star to the Earth, which we call the Sun, is far from the largest. Despite the fact that at the moment humanity has been able to explore only a small part of the Universe, exactly as many stars and other space objects as modern equipment allows us to record and study, it is already known for certain that there are much larger luminaries, in comparison with which the Sun looks like space speck of dust. The ten largest stars are known to every person interested in astronomy.

Despite their remoteness, for the most part they are perfectly visible in the night sky, because a powerful stream of light from them is able to overcome great distances. So, what are they - the largest stars of the universe known to man?

Super giant of the constellation Scorpio Antares

Starting a story about the largest stars, it is necessary to pay attention to the supergiant from the constellation Scorpio - the red star has a radius approximately equal to 1200-1500, or a little more, solar radii. More accurate data is not yet available. The distance of this object from the Earth is approximately 12 thousand sv. years. The object is visible in the sky with the naked eye.

Bright star in the constellation Cygnus

KY Cygnus is also the largest star known to modern mankind in terms of size. The distance from this object to the Earth is approximately 5 thousand light years. The star has its own oddities - its mass exceeds the solar mass only 25 times, and its equatorial radius is 1420 solar. This object emits a million times more light than the Sun, which also makes it very visible on the horizon.

Look at the night sky and see that it is filled with stars. But with the naked eye, only a microscopic fraction of them can be seen. 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 variety of colors and sizes - and next to many of them, our Sun looks like a crumb. But which star will be the true giant of the heavens? It’s worth starting with a definition of what we mean by a giant. Will it be the star with the largest radius, for example, or the one with the largest mass?

galactic giants

The star with the largest radius is probably UY Scuti, a bright variable supergiant in the constellation Scutum. Located 9500 light-years from Earth and made of hydrogen, helium and other heavier elements, almost the composition of our Sun, this star in radius bypasses it in 1708 (plus or minus 192) times.

The circumference of the star is about 7.5 billion kilometers. You would have to fly a plane for 950 years to completely circle it - and even light would take six hours and 55 minutes. If we replaced 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 enormous size and a possible mass of 20-40 times the Sun's (2-8×10³¹kg), UY Scutum would 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. Being 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, there was 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 heavier elements, is not much larger than the Sun, 35 times its radius, but it is 265 times more massive - which is remarkable, given that in 1.5 million years of its life it has already lost 55 solar masses.

The type of Wolf-Rayet stars is far from stable. They look like a blurry blue sphere without a clear surface, blowing incredibly powerful stellar winds. Such winds travel at 2,600 km/s, 65 times faster than the Juno probe, the fastest man-made object.

As a result, the star is losing mass at a rate of 3.21×10¹⁸ kg/s, equivalent to Earth's loss in 22 days.

These space rock stars burn out quickly and die quickly. R136a1 radiates nine million times more energy than our Sun and would appear 94,000 times brighter than the Sun to our eyes if it took its place. In fact, it is the brightest star ever discovered.

its surface is over 53,000 degrees Celsius (), and such a star will live no more than two million years. Her death will be marked by a colossal supernova explosion, which 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 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?

An illustration of R136a1, the most massive star known to date. Credit & Copyright: Sephirohq / Wikipedia.

Look at the night sky - it is filled with stars. However, only a microscopic part of them is visible to the naked eye. In fact, scientists estimate that there are 10,000 billion galaxies in the visible universe, each with more than a hundred billion stars. And this is neither more nor less than 10 24 stars. These spectacular thermal stations come in a variety of colors and sizes – and many of them make our Sun look tiny. However, which star is a true cosmic giant? First, we need to define the concept of a giant star: should it have the largest radius or the largest mass?

To date, the star with the largest radius is recognized as the star UY Scuti (Scuti), a variable red supergiant in the constellation Scutum. It is more than 9,500 light-years distant from us, and consists mostly of hydrogen and helium, as well as a number of other heavier elements. In terms of chemical composition, UY Scutum resembles our Sun, but has a radius 1708 (± 192) times greater than that of our star. That is almost 1,200,000,000 km, making its circumference more than 7.5 billion kilometers. To make it easier to understand such dimensions, one can imagine an aircraft that would take 950 years to fly around UY Scutum - and even if the aircraft could travel at the speed of light, its journey would last 6 hours and 55 minutes.

If we place UY Scutum in place of our Sun, then its surface will pass somewhere between the orbits of Jupiter and Saturn - it goes without saying that the Earth in this case will be swallowed up. Given the huge size and mass of 20 to 40 solar masses, one can calculate that the density of the UY Shield is only 7×10 -6 kg/m 3 . In other words, it is more than a billion times less than the density of water. Indeed, if we could put this star in a pool, then theoretically it would float. Being over a million times less dense than Earth's atmosphere, UY Shield would float like a balloon in the air.

But if these crazy facts didn't surprise you, then let's move on to the heaviest star. The heavyweight star R136a1 is located in the Large Magellanic Cloud, approximately 165,000 light-years away. This star is only 35 times the size of our Sun, yet it is 265 times as massive as our Sun - which is really amazing given the fact that it has already lost 55 solar masses in its 1.6 million years of life.

R136a1 is a highly unstable Wolf-Rayet type star. It appears as a blue ball with an indistinct surface, which constantly generates extremely powerful stellar winds. These winds move at speeds up to 2600 km/s. Due to such high activity, R136a1 loses 3.21×10 18 kg/s of its mass, which is about one Earth every 22 days. Stars of this type shine brightly and die quickly. R136a1 radiates nine million times more energy than our Sun. Its brightness is 94,000 times the brightness of the Sun. In fact, it is the brightest star ever found. The temperature on its surface is more than 53,000 Kelvin, and it has only two million years to live, after which it will explode as a supernova.

Of course, against such giants, our Sun seems like a dwarf, but over time it will also increase in size. In about seven and a half billion years, it will reach its largest size and become a red giant.

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 whose radius 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 Shield - 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 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 Carina, a double giant star in the 19th century, as a result of an outburst, a nebula formed around this system, 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.