A dwarf nova (pl. novae ), or U Geminorum variable , is one of several types of cataclysmic variable star , consisting of a close binary star system in which one of the components is a white dwarf that accretes matter from its companion. Dwarf novae are dimmer and repeat more frequently than "classical" novae.
5-522: VW Hydri is a dwarf nova of the SU Ursae Majoris type in the deep southern constellation Hydrus ; a star system that consists of a white dwarf and another generally cool star. It is one of the brightest dwarf novae systems in the sky. These systems are characterised by frequent eruptions and less frequent supereruptions. The former are smooth, while the latter exhibit short "superhumps" of heightened activity. The white dwarf sucks matter from
10-600: A cooler, duller mode. Dwarf novae are distinct from classical novae in other ways; their luminosity is lower, and they are typically recurrent on a scale from days to decades. The luminosity of the outburst increases with the recurrence interval as well as the orbital period; recent research with the Hubble Space Telescope suggests that the latter relationship could make dwarf novae useful standard candles for measuring cosmic distances. There are three subtypes of U Geminorum star (UG): In addition to
15-410: The accretion disk, when gas in the disk reaches a critical temperature that causes a change in viscosity , resulting in a temporary increase in mass flow through the disc, which heats the whole disc and hence increases its luminosity. The mass transfer from the donor star is less than this increased flow through the disc, so the disc will eventually drop back below the critical temperature and revert to
20-461: The other star onto an accretion disc and periodically erupts, reaching apparent magnitude 8.4 in superoutbursts , 9.0 in normal outbursts and remaining at magnitude 14.4 when quiet. Normal outbursts occur every 27.3 days and last for 1.4 days, while superoutbursts happen 179 days and last for 12.6 days. This variable star–related article is a stub . You can help Misplaced Pages by expanding it . Dwarf nova The first one to be observed
25-483: Was U Geminorum in 1855; however, the mechanism was not known until 1974, when Brian Warner showed that the nova is due to the increase of the luminosity of the accretion disk. They are similar to classical novae in that the white dwarf is involved in periodic outbursts, but the mechanisms are different. Classical novae result from the fusion and detonation of accreted hydrogen on the primary's surface. Current theory suggests that dwarf novae result from instability in
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