Largest Star Ever Known in the Universe

VY Canis Majoris (VY CMa) is a red hypergiant star located in the constellation Canis Major. With a size of 2600 solar radii, it is the largest known star and also one of the most luminous known. It is located about 1.5 kiloparsecs (4.6×10¹⁶ km) or about 4,900 light years away from Earth. Unlike most stars, which occur in either binary or multiple star systems, VY CMa is a single star (i.e. does not have any stellar companions). It is categorized as a semiregular variable and has an estimated period of 6,275,081 days, or just under 17,200 years.

VY canis majoris compare to Sun

The first known record of VY Canis Majoris is in the star catalogue of Jérôme Lalande, on March 7, 1801. The catalogue listed VY CMa as a 7th magnitude star. Further studies on its apparent magnitude during the 19th century showed that the star has been fading since 1850.
Since 1847, VY CMa has been known to be a red star.During the 19th century, observers measured at least six discrete components to VY CMa, suggesting the possibility that it is a multiple star. These discrete components are now known to be bright areas in the surrounding nebula. Visual observations in 1957 and high-resolution imaging in 1998 showed that VY CMa does not have a companion star.
VY CMa is a high-luminosity M star with an effective temperature of about 3,000 K, placing it at the upper-right hand corner of the Hertzsprung–Russell diagram and suggesting that it is a highly evolved star. During its main sequence, it would have been an O star with a mass of about 30 to 40 M_?.

VY Canis Majoris

What would happen if VY Canis Majoris went Nova?

When VY Canis Majoris dies, it will die as a core-collapse supernova or even a hyper-nova depending on it’s mass and composition. It’s huge size does not necessarily mean it will explode as a hyper-nova and give rise to a gamma ray burst when some or all of the star becomes a black hole. Even so, it’s much more likely to explode as a core-collapse supernova that will produce a neutron star or a black hole depending on what happens when it’s core is converted into iron. When that happens, the outer layers will initially be ejected back into space at speeds of 5,000 miles per second or more, and the wreckage will outshine the entire galaxy for weeks or months. If VY Canis Majoris had any planets, they would be at the minimum ejected into space due to the sudden loss of 90 percent or more of the star’s mass back to space. Their atmospheres and surface water if present would be flash boiled away into space, and likely their surfaces would melt from being hit with billions of times more energy than they received before. It’s indeed possible they would simply be vaporized in the explosion. If there are any life bearing planets within a few light years of VY Canis Majoris when it blows, all life would be destroyed. Any inhabited planets within 30 or 50 light years of the explosion will either be sterilized or suffer severe mass extinctions due to the massive blast of gamma and x-rays disrupting the ozone layer. Dangerous, even deadly doses of radiation will kill or injure any complex, multi-cellular life forms but single cell microbes can withstand radiation fields that would instantly kill humans and most other higher forms of life. Star systems farther away would be exposed to much more ionizing radiation and cosmic rays, which would induce mutations and leave traces in the soil, ice sheets and oceans, but would not trigger wide spread die offs of species wholesale. From several hundred light years away, VY Canis Majoris’ demise would be no threat to a habitable planet, but a bonanza for astronomers interested in the lives and deaths of stars and how they made our own existence possible. If however, VY Canis Majoris is massive enough and has the right composition to explode as a hyper-nova, the resulting gamma ray burst will destroy life on planets caught in the jets spat out by the newly born black hole thousands of light years away. These jets form along the doomed star’s axis of rotation, and are highly focused like laser beams. If an inhabited planet is not in the way, it would survive unharmed unless it was in close proximity to the supernova. A planet or life on that planet caught in the jet is doomed. Planets within a 100 light years would melt or vaporize from the jet’s onslaught, which are composed of high energy plasma moving at nearly the speed of light.They are nature’s ultimate death ray, much like the Death Star out of the Star Wars movies.