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VY Canis Majoris (VY CMa) is currently the largest known star and also one of the most luminous. Located in the constellation Canis Major, it is a red hypergiant, between 1800 and 2100 solar radii, 8.4–9.8 astronomical units in radius, 3.063 billion km or 1.7 billion miles in diameter, and about 1.5 kiloparsecs (4,900 light years, 4.6×1016 km or 2.9×1016 mi) distant from Earth. Unlike most hypergiant stars, which occur in either binary or multiple star systems, VY CMa is a single star. It is categorized as a semiregular variable and has an estimated period of 2,000 days. It has an average density of 0.000005 to 0.000010 kg/m3. Placed in our solar system, VY Canis Majoris's surface would extend beyond the orbit of Saturn, although the astrophysicists Philip Massey, Emily Levesque and Bertrand Plez disagree about the star's stated radius, suggesting it is smaller: merely 600 times the size of the Sun, extending past the orbit of Mars. The first known recorded observation of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on March 7, 1801, which lists VY CMa as a 7th magnitude star. Further 19th-century studies of its apparent magnitude demonstrate that the star has been fading since 1850. University of Minnesota Professor Roberta M. Humphreys estimates the radius of VY CMa at 1,800 to 2,100 solar radii. To illustrate, if Earth's Sun were replaced by VY Canis Majoris, its radius might extend beyond the orbit of Saturn (about 9 AU). Assuming the upper size limit of 2100 solar radii, light would take more than 2.7 hours to travel around the star's circumference, compared to 14.5 seconds for the Sun. It would take 7×1015 Earths to fill the volume of VY Canis Majoris. If the Earth were to be represented by a sphere one centimeter (0.39") in diameter, the Sun would be represented as a sphere with a diameter of 109 centimeters (3½ ft.), at a distance of 117 meters. At these scales, VY Canis Majoris would have a diameter of approximately 2.3 kilometers (1.43 mi.), assuming the upper limit estimate of its radius. The star has been discovered to be very unstable, having thrown off much of its mass into its surrounding nebula. Astronomers, with the help of the Hubble Space Telescope, have predicted that VY Canis Majoris will be blown up, as a hypernova, in less than 100,000 years. Theoretically, a hypernova would cause gamma ray bursts that could damage the contents of nearby solar systems (2-5 lightyears), but VY Canis Majoris is much too far away for its explosion to affect Earth in any way. [READ THE REST OF THIS ARTICLE]
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