VY Canis Majoris or VY CMa is a red hypergiant star. It is located in the constellation Canis Major. It is one of the largest and brightest red hypergiants observed so far. It has a diameter of 1800 solar radii. This star emits energy very quickly and therefore, only exists for a few million years. It is estimated to be 4900 light-years away from Earth. This star shows periodic light changes that last for approximately 2200 days.
The crimson star
The first known recorded observation of VY Canis Majoris is in the star catalog of Jérôme Lalande, who recorded it on 7th March 1801. Since 1847, VY CMa has been known to be a crimson star. Originally, University of Minnesota Professor Roberta M. Humphreys approximated that the radius of VY CMa is 1800-2100 times that of the Sun. This would make it the largest known star based on its radius.
A big star
There have been conflicting opinions of the properties of VY CMa. A commonly held theory states that the star is a very large and luminous red hypergiant. However, various larger estimates of the size and luminosity fall outside the bounds of current stellar theory. In another theory, the star is a normal red supergiant with a radius around 600 times that of our Sun.
The surface of VY CMa
This star also illustrates the conceptual problem of defining the “surface” of very large stars. This is very important for multiple reasons, including determining its radius and thus its size. It is a hundred thousand times less dense than the atmosphere of Earth (air) at sea level. Its average density is 0.000005 to 0.000010 kg per metre³. Additionally, the star is constantly losing mass at an astounding rate. The boundary of such a star is usually defined by its “Roseland Radius”, which is based on its opaqueness to light.
Compiled by: Madhurani Chavan