The stars are huge balls of burning plasma. But, with the exception of the Sun, they appear as tiny dots of light in the night sky. Moreover, our Sun is not the smallest or largest star. There are many stars that are much more massive and larger than the Sun. Some of them have evolved since their inception. Others grow as they "age."
To answer the question of what is the largest star in the universe, we "sorted" the stars by such a criterion as size. The unit of measurement of the stellar radius was taken to be the equatorial radius of the Sun, which is 696,392 kilometers.
10.V766 Centauri
This celestial body, also known under a different name (HR 5171 A), belongs to yellow hypergiants and is a double star. Its smaller “partner” HR 5171 B orbits V766 Centauri in 1300 Earth days.
9.VV Cephei A
This star is located in the direction of the constellation Cepheus, about 5 thousand light-years from Earth. The red hypergiant with a radius of approximately 1050-1900 solar radii is part of a binary star system. Its companion is the small blue star VV Cepheus B, which orbits its "big brother" in an elliptical orbit. The star is named after the largest of the pair, and is now known as one of the largest binary stars in the Milky Way.
8. AH Scorpio
To get to know this red supergiant from the constellation Scorpio, people would have to travel a distance of 7,400 light years. The radius of AH of Scorpio exceeds the solar one by 1411 times.
7.VY Big Dog
There is a heated debate among astronomers associated with this star. According to estimates revised in 2012, its radius exceeds the radius of the Sun by 1420 times. However, according to an initial estimate by Robert Humphreys, the VY radius of Canis Major is 1800 to 2200 times that of the Sun. The exact radius of the stellar giant has not yet been established. When it will be possible to find out for sure, the leader in the rating of the largest stars may change.
6.KY Swan
The radius of this hypergiant star is at least 1,420 times the radius of the Sun, and the brightness level is as much as 300,000 times that of the Sun. It is located in the constellation Cygnus, about 5 thousand light-years from Earth.
5.VX Sagittarius
This star belongs to the class of hypergiants - the most powerful and brightest, the heaviest and at the same time the rarest and shortest-lived supergiants. Its radius exceeds the solar one by about 1520 times.
VX Sagittarius is located in the constellation Cepheus, 9000 light-years from our planet. It is so huge that it can easily cover the orbital path of Saturn if it happens to be in the place of the Sun. The star's red color indicates that its temperature range is 3000 to 4000 Kelvin. Hotter stars are yellow in color, and very hot ones become bluish.
4. Westerland 1-26
At a distance of 11,500 light-years from our planet, in the star cluster Westerland 1, is the fourth largest star in the galaxy.In luminosity, it is 380 thousand times greater than the Sun, and if placed in the place of our yellow star with its photosphere, it would absorb the orbit the largest planet in the solar system - Jupiter. The photosphere is where the star becomes transparent to light, and where photons - that is, light particles - can disappear. The photosphere allows astronomers to roughly know about the "edges" of a star.
3. RW Cephei
Here is another star known to science from the constellation Cepheus, was included in the list of the largest. The radius of this red supergiant is about 1600 solar radii. If RW Cephei were in the place of the Sun, the radiating layer of its stellar atmosphere (photosphere) would extend beyond the orbit of Jupiter.
2. WOH G64
The second largest star in space is located in the constellation Golden Fish, 160 thousand light-years from our world. Despite the fact that this star has lost up to a third of its original mass due to stellar wind, a long-term thick annular layer of a torus of gas and dust has formed around it. The "dimensions" of the star have been adjusted to take into account all the mass present in its ring. It is expected to go supernova in a couple of thousand years.
1. UY Shield (UY Scuti) - the largest star in the universe
The largest star in the world is located at a distance of 9,500 light years from the Sun, in the constellation of the Shield. Its approximate size is almost eight astronomical units, where one astronomical unit is the distance between the Earth and the Sun. This is enough to extend the photosphere of the UY Shield into Jupiter's orbit.
The UY Shield is so gigantic and so bright that you can see it through powerful binoculars on a dark night. It is visible along the stars of the Milky Way, and outwardly looks like a reddish star with a faint spot.
Study of a supergiant
In the summer of 2012, astronomers, using the Very Large Telescope complex located in the Atacama Desert in Chile, measured the parameters of three red supergiants near the Galactic Center region. The objects of study were UY Shield, AH Scorpio and KW Sagittarius.
Scientists have determined that all three stars are 1,000 times larger and more than 100,000 times brighter than the Sun. They also made the discovery that UY Shield is the largest, brightest of all three stars. The effective temperature was obtained from the radius and luminosity - 3665 ± 134 K.
Mass and dimensions of the UY Shield in comparison with the Sun
The exact mass of this star is unknown, primarily because it has no visible companion star, thanks to which its mass can be measured by studying gravitational interference. According to stellar evolutionary models, the initial mass of a star (during its formation), corresponding to a red supergiant stage, such as that of UY Shield, would be about 25 M☉ (possibly up to 40 M☉ for a non-rotating star) and constantly burned out. Its current mass is estimated to be 7-10 M☉ and continues to decrease. UY Shield is not only the largest, but also the fastest burning star currently known to science.
The mass of the UY Shield is just over 30 times that of our Sun, which does not even come close to the top of the list of the most massive stars. This honor belongs to the star R136a1, which is 265 times the mass of the Sun, but at the same time in radius is only 30 times the radius of the Sun.
Mass and physical sizes do not always correlate for celestial bodies, especially for giant stars. Thus, although the UY of the Shield is only 30 times more massive than the Sun, it has a radius somewhere in the region of 1,700 times that of our daylight. The error of this measurement is about 192 solar radii.
Is life near UY Scuti possible
The habitable zone or the orbital zone with the highest probability of life is a complex thing, the possibility of which depends on several factors. The planet on which life originated should not be too far or too close to the star. According to astronomers' calculations, the habitable zone around the UY Shield will be from 700 to 1300 astronomical units (AU). This is an insanely long distance. The number in kilometers is simply incomprehensible - it is about 149 597 870 700 km.For comparison: the habitable zone in the solar system is located at a distance of 0.95 to 1.37 AU from the Sun.
If a living planet is at a safe distance, say 923 astronomical units from the UY Shield, a year on it will last 9612 Earth years. It's almost 2,500 years of winter! And 2500 years of summer. That is, many generations will change who know only one season.
Shield UY may indeed have a planetary system in this zone, but if it does, it will not exist for very long. You, the reader, may reasonably ask: "Why?" Because the future of the star is too bright.
What the future holds for the star
Based on current models of stellar evolution, scientists suggest that Shield UY has begun pouring helium into a shell around the core. As helium flows out, the star will begin to merge heavier elements such as lithium, carbon, oxygen, neon, and silicon. The location of the star deep in the Milky Way suggests that it is rich in metal. After the heavy elements merge, its core will begin to produce iron, upsetting the balance of gravity and radiation, leading to a supernova. This will happen in a million years - not very long by astronomical standards, but humanity has time to prepare for such an enchanting spectacle.
After a supernova, UY Shield will most likely turn into a yellow hypergiant, a blue variable star, or even a Wolf-Rayet star with very high temperature and luminosity. In the latter case, it will "give birth" to many new stars following its supernova.