NML Cygni or V1489 Cygni is a red hypergiant star. It is one of the largest stars known at present. One study says its radius is 1,640 times the Sun's radius (solar radii), but an older study from 2010 says its radius is only 1,183 solar radii. It is one of the brightest supergiant stars. It was discovered in 1965, by Gerry Neugebauer, D.M. Martz and Robert Leighton. The name 'NML' comes from the names of the three discoverers.
NML Cygni's distance from Earth is about 5,250 light-years. This star has dust surrounding it. It has a bean-shaped asymmetric nebula with water vapour. It is a semiregular variable star. This means its brightness changes over 940 days.
This star is a part of the Cygnus OB2 association, which is 1.74 ± 0.2 kpc away. This is one of the nearest massive star groups to the Sun. This group includes some of the most massive and brightest stars known, including the suspected luminous blue variable Cyg OB2 #12. NML Cygni has lots of oxygen. Molecules like H2O, Silicon monoxide, carbon monoxide, hydrogen cyanide, carbon monosulfide, sulfur monoxide, sulfur dioxide and hydrogen sulfide are also in the star.
NML Cygni has two dense outer layers of dust and molecules. The star is also losing mass by slowly throwing gas into space. The dust envelopes are formed by this process.