VV Cephei

VV Cephei (vv Cep/HD 208816) is a variable star located in the constellation of Cepheus of apparent magnitude + 4.91. It is a binary star composed of a red supergigante2, vv Cephei A, and a white-bluish star of the main sequence, vv Cephei B. The system is about 3000 light-years from the Solar system.

VV Cephei A

Size comparison between the sun (the yellow dot on the left) and VV Cephei A.
VV Cephei A is a luminous red supergiant of spectral type M2Iape, being one of the biggest stars known with a radius between 14001 times the solar radio. Translated into astronomical units (UA), it has a radius between 4.7 and 10.4 UA, which implies that if it were in the place of the sun — considering the maximum value — its surface would extend beyond the orbit of Jupiter. Its surface temperature is not well known, amounting in the range of 3300-3650 K. Being very far from the Earth, the distance is uncertain, so its luminosity can be between 163,000 and 535,000 times the sun. Its mass is estimated between 25 and 40 solar masses.

VV Cephei A does not have spherical shape, but because of the tidal force produced by the gravitational attraction of its companion, it is shaped of gout and yields material to a disc that is formed around VV Cephei B. Likewise, it is a pulsating star semiregular whose brightness varies From hundredths to tenths of magnitude. Different periods of oscillation of 58, 118 and 349 days are known, as well as another longer of 13.7 years. A star of these characteristics (at the moment fusing helium in carbon atoms) cannot end its days but as a supernova, whose explosion can expel its partner at great speed by turning it into a fugitive star.

VV Cephei B
VV Cephei B is much less known than his huge companion. Catalogued as a B8Ve star, its mass can be several times greater than the solar mass. Mass transfer between the two stars is likely to produce sudden changes in the system's orbital period. Currently VV Cephei B moves in an eccentric orbit at a distance of vv Cephei between 17 and 34 UA, the orbital period of 20.4 years. When VV Cephei a passes in front of VV Cephei B an eclipse of 250 days of duration is produced that makes its brightness decrease by 20%.