What is VY Canis Majoris?

VY Canis Majoris is the largest known star.

The largest known star is VY Canis Majoris, a red hypergiant measuring between 1800 and 2100 solar radii. Its volume is nearly a billion times that of the Sun, although its density is much smaller. Canis Majoris means big dog in Latin. If it were located in the solar system, its surface would reach all the way to the orbit of Saturn. Another way of saying this is that this star is about 9 astronomical units (AUs) wide, nine times the distance between the Earth and the Sun. There must be bigger stars located in other galaxies, but we currently don’t have telescopes powerful enough to resolve them. Hyperteloscopes can help in this regard.

Eventually, the star VY Canis Majoris will collapse in a supernova explosion and become a black hole.

VY Canis Majoris is a star in his final death throes. It is ejecting massive amounts of material into a surrounding nebula that makes the star locked into the visible spectrum. It should be observed in the infrared portion of the spectrum. The star’s death nebula is about 4500 AU wide, about fifty times larger than the star itself, and much larger than our solar system. Within the gas nebula is a smaller circumstellar dust region, which has a temperature of 760 K and a width of approximately 260 AU. The star’s surface probably has a temperature around 3650 K, extremely cold for a star.

Current telescope technology makes it impossible to find stars larger than VY Canis Majoris.

Unlike main sequence stars like our Sun, VY Canis Majoris has no distinct photosphere and therefore just disappears into space. While it is the largest known star, it is definitely not the most massive, in part because it has already ejected much of its mass into the surrounding nebula.

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Like all red giants and hypergiants, the VY Canis Majoris is so big because it has exhausted all the hydrogen fuel in its core and has started fusing hydrogen into a shell outside a helium core. In fact, VY Canis Majoris is so huge that it can fuse helium, lithium, and so on, all the way up the periodic table to iron and beyond. Eventually, it will have a core made mostly of iron, just like the planets. The problem with post-iron fusion reactions is that they do not produce energy and therefore cannot balance the gravitational pressure generated by the star. When all the fusion fuel is gone, the star will catastrophically collapse in a supernova explosion and become a black hole.

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