VY Canis Majoris (VY CMa) is an exceptionally large, luminous red hypergiant star located in the constellation Canis Major.
With a radius about 1,420 times that of the Sun, corresponding to a diameter of 13.2 astronomical units, VY Canis Majoris is one of the largest known stars in the Milky Way. The star lies at an approximate distance of 3,840 light years from Earth and has an apparent magnitude that varies from 6.5 to 9.6. It is classified as a semiregular variable star and has an estimated period of 2,000 days.
Hypergiants are stars with enormous luminosity that lose mass at a very high rate. With an estimated luminosity about 270,000 times that of the Sun, VY Canis Majoris is one of the most luminous members of its class. The star is losing an enormous amount of mass – about 30 times the mass of the Earth every year – as it enters the final stage of its life before exploding as a supernova.
The cloud of expelled material – dust and gas – is pushed away by the star’s radiation pressure and it keeps moving outwards. The dust and gas will eventually be used by new stars, along with the heavier elements left behind by the supernova, possibly to form planets.
VY Canis Majoris was first catalogued by the French astronomer Jérôme Lalande on March 7, 1801. Lalande listed it as a 7th magnitude star.
Other 19th century observations revealed that the star has been fading since 1850. At the time, VY Canis Majoris was suspected to be a multiple star, but now the components that were detected by 19th century observers are known to be bright patches in the nebula surrounding the star. VY Canis Majoris was confirmed not to have any companions by visual observations in 1957 and imaging in 1998.
The star’s properties indicate that it was an O-type star with an estimated mass between 15 and 35 times that of the Sun during its main sequence.
The diameter of VY CMa, 13.2 astronomical units, corresponds to about 1,976,640,000 kilometres. While different sources give different estimates of the hypergiant’s radius, if it were placed at the centre of our solar system, the star’s surface would extend well beyond the orbit of Jupiter.
Astronomers originally estimated the star’s radius at 1,800 to 2,100 solar radii, which made VY CMa the largest star known at the time. More recent estimates give it a radius of about 1,420 solar radii. This still makes VY CMa considerably larger than Betelgeuse, which has a radius about 1,180 times solar, Antares, estimated to be 883 times larger than the Sun, and many other known large stars.
It is, however, smaller than VX Sagittarii, an evolved red supergiant in Sagittarius (1,520 solar radii), Westerlund 1-26 (1,530), a red supergiant or hypergiant located in Ara constellation, WOH G64 (1,540 – 1,730), a red hypergiant located in the Large Magellanic Cloud in Dorado, the orange hypergiant RW Cephei (1,636) in Cepheus, the red hypergiant NML Cygni (1,642 – 2,775) in Cygnus, and the red supergiant UY Scuti (1,708), located in the constellation Scutum.
VY Canis Majoris compared to the Sun
VY Canis Majoris is large enough to produce a hypernova, or superluminous supernova, when it explodes. Hypernovae produce a considerably higher amount of energy than regular supernovae, as well as long-duration gamma ray bursts, which are among the most energetic events observed in the universe.
When VY CMa explodes, it may release more energy than 100 standard supernovae, as well as enormous quantities of gamma rays. Being almost 4,000 light years away, the star is too distant from Earth for its explosion to affect us, but the hypernova event would almost certainly destroy any life on any planets in its range.
VY Canis Majoris
Constellation: Canis Major
Right ascension: 07h 22m 58.32877s
Declination: −25° 46′ 03.2355″
Spectral class: (M2.5I-)M3-M4.5
Apparent magnitude: 6.5 to 9.6 (7.9607)
Distance: 3,840 light years (1,170 parsecs)
Variable type: semiregular
Mass: 30 to 40 solar masses
Radius: 1,420 ± 120 solar radii
Luminosity: 270,000 solar luminosities
Temperature: 3,490 K
Radial velocity: 41 km/s
Designations: VY Canis Majoris, VY CMa, HD 58061, CD -25 4441, HIP 35793, AAVSO 0718-25
Zooming in on Massive Hypergiant Star VY Canis Majoris
Credits: ESO, Digitized Sky Survey 2, N. Risinger (skysurvey.org)