Stars are huge balls of burning plasma. But, with the exception of the Sun, they look like tiny dots of light in the night sky. And our Sun is not the smallest or the largest star. There are many stars much more massive and larger than the Sun. Some of them have evolved since they formed. Others grow as they "age."
To answer the question, what is the biggest star in the universe, we "sorted" the stars by such a feature as size. The equatorial radius of the Sun, which is 696,392 kilometers, was taken as the unit of measurement of the stellar radius.
10. V766 Centauri
This celestial body, also known by another name (HR 5171 A), is a yellow hypergiant and a double star. Its smaller "partner" HR 5171 B orbits V766 Centauri in 1,300 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 Cephei B, which revolves around its "big brother" in an elliptical orbit. The star is named after the larger of the pair, and is now known as one of the largest binary stars in the Milky Way.
8. AH Scorpio
To get a closer look at this red supergiant in the constellation Scorpius, humans would have to travel 7,400 light years. The radius of AH Scorpii is 1,411 times that of the Sun.
7. VY Canis Majoris
This star is the subject of heated debate among astronomers. According to estimates updated in 2012, its radius is 1,420 times that of the Sun. However, according to Robert Humphreys' initial estimate, the radius of VY Canis Majoris is 1,800 to 2,200 times that of the Sun. The exact radius of the stellar giant has not yet been determined. When it becomes known for sure, the leader in the ranking of the largest stars may change.
6. KY Swan
This hypergiant star has a radius at least 1,420 times that of the Sun and a brightness level 300,000 times that of the Sun. It is located in the constellation Cygnus, about 5,000 light years from Earth.
5. VX Sagittarius
This star belongs to the class of hypergiants - the most powerful and brightest, heaviest and at the same time the rarest and shortest-lived supergiants. Its radius exceeds the Sun's by approximately 1520 times.
VX Sagittarii is located in the constellation Cepheus, 9,000 light years from our planet. It is so huge that it could easily cover the orbital path of Saturn if it were to occupy the position of the Sun. The star's red color indicates that its temperature ranges from 3,000 to 4,000 Kelvin. Hotter stars have a yellow color, while very hot ones acquire a bluish tint.
4. Westerland 1-26
At a distance of 11,500 light years from our planet, in the star cluster Westerland 1, lies the fourth largest star in the galaxy. It is 380 thousand times more luminous than the Sun, and if placed in the place of our yellow star, its photosphere would absorb the orbit of the largest planet in the Solar System, Jupiter. The photosphere is the place where a star becomes transparent to light, and where photons, or light particles, can disappear. The photosphere allows astronomers to approximately learn about the “edges” of a star.
3. RW Cephei
Here is another star known to science from the constellation Cepheus that made it onto the list of the largest. The radius of this red supergiant is about 1600 solar radii. If RW Cephei were to be 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 Dorado, 160,000 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 multi-year thick ring layer of gas and dust torus 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 become a supernova in a couple of thousand years.
1. UY Scuti is the largest star in the universe.
At a distance of 9,500 light-years from the Sun, in the constellation Scuti, lies the largest star in the world. 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 UY Scuti into the orbit of Jupiter.
UY Scuti is so huge and so bright that you can see it with powerful binoculars on a dark night. It is visible along the Milky Way, and appears as a reddish star with a faint spot.
Studying the supergiant
In the summer of 2012, astronomers used the Very Large Telescope in the Atacama Desert in Chile to measure the parameters of three red supergiants near the Galactic Center. The objects of study were UY Scuti, AH Scorpii, and KW Sagittarii.
Scientists have determined that all three stars are 1,000 times larger and more than 100,000 times brighter than the Sun. They also discovered that UY Scuti is the largest and brightest of the three stars. The effective temperature of 3,665 ± 134 K was obtained from the radius and luminosity.
Mass and size of UY Scuti compared to the Sun
The exact mass of this star is unknown, primarily because it has no visible companion star, through which its mass can be measured by studying gravitational interference. According to stellar evolutionary models, the initial mass of a star (at its formation), corresponding to a red supergiant stage like UY Scuti, would have been about 25 M☉ (possibly up to 40 M☉ for a non-rotating star) and was constantly burning out. Its current mass is thought to be 7-10 M☉ and is continuing to decrease. UY Scuti is not only the largest star known to science, but also the fastest burning star.
UY Scuti is just over 30 times the mass of our Sun, which doesn't even come close to the top of the list of most massive stars. That honor goes to R136a1, which is 265 times the mass of the Sun, but only 30 times the radius of the Sun.
Mass and physical size do not always correlate for celestial bodies, especially for giant stars. Thus, although UY Scuti 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 star. The uncertainty in this measurement is about 192 solar radii.
Is Life Possible Around UY Scuti?
The habitable zone, or the orbital zone with the highest probability of life, is a complex thing, and its likelihood of occurrence depends on several factors. A planet that could host life would have to be neither too far nor too close to its star. Astronomers estimate that the habitable zone around UY Scuti would be between 700 and 1,300 astronomical units (AU). That's an insanely large distance. The number in kilometers is simply incomprehensible - it's about 149,597,870,700 km. For comparison, the habitable zone in the Solar System is between 0.95 and 1.37 AU from the Sun.
If a living planet is at a safe distance, say 923 astronomical units from UY Scuti, a year on it will last 9,612 Earth years. That's almost 2,500 years of winter! And 2,500 years of summer. That means many generations that know only one season.
UY Scuti may indeed have a planetary system in this zone, but if it does, it won't last very long. You, the reader, might reasonably ask, "Why?" Because the star's future is just too bright.
What does the future hold for the star?
Based on current models of stellar evolution, scientists suggest that UY Scuti has begun to fuse helium into a shell around its core. As the helium runs out, the star will begin to fuse heavier elements, such as lithium, carbon, oxygen, neon, and silicon. The star's location deep in the Milky Way suggests that it is rich in metal. After the fusion of heavier elements, its core will begin to produce iron, upsetting the balance of gravity and radiation, causing a supernova. This will happen in a million years - not very long in astronomical terms, but humanity has time to prepare for such a spectacular spectacle.
After the supernova, UY Scuti will likely become 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.
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