V Sagittae

V Sagittae or V Sge is a cataclysmic variable binary star system in the constellation Sagitta that is expected to go nova and briefly become the most luminous point of light in the Milky Way and the brightest stars in our sky around the year 2083.[3][4] The system is composed of a main sequence star of about 3.3 solar masses and a white dwarf of about 0.9 solar masses; the fact that the white dwarf is less massive than its companion is highly unusual,[3] and V Sge is the only super soft X-ray source nonmagnetic cataclysmic variable found so far.

V Sagittae

Location of V Sagittae (circled) in Sagitta
Observation data Epoch J2000      Equinox J2000
Constellation	Sagitta
Right ascension	20h 20m 14.691s[1]
Declination	+21° 06′ 10.44″[1]
Apparent magnitude (V)	8.6-13.9[2]
Characteristics
Variable type	eclipsing and cataclysmic[2]
Astrometry
Proper motion (μ)	RA: -2.052[1] mas/yr Dec.: -6.485[1] mas/yr
Parallax (π)	0.4190 ± 0.0320[1] mas
Distance	7,800 ± 600 ly (2,400 ± 200 pc)
Other designations
AAVSO 1015+20, V Sge, GSC 01643-01764
Database references
SIMBAD	data

V Sge has brightened by a factor of 10 over the last century, and based on research reported in 2020, it is expected to continue to brighten and briefly become the brightest star in the night sky sometime around 2083, plus or minus about 11 years.[5] Over the last few months and days the pair will coalesce and go nova, eventually becoming a red giant star.

The stars currently orbit each other about every 0.514 days, and eclipse each other each orbit. The pair is in the late stages of an in-spiral, and the period is decreasing at a rate of 4.73 * 10^-10 days/cycle.

Material from the larger star is accreting onto the white dwarf at an exponentially increasing rate, generating a huge stellar wind. The doubling time is about 89 years.