A dwarf nova is a type of cataclysmic variable, consisting of a close binary star system in which one of the components is a white dwarf, which accretes matter from its companion. 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, while current theory suggests that dwarf novae result from instability in the accretion disk, when gas in the disk reaches a critical density that causes it to collapse onto the white dwarf, releasing large amounts of gravitationalpotential energy.[1],(S&T) Artists conception of a cataclysmic variable system Cataclysmic variables are a class of binary stars containing a white dwarf and a companion star. ... Artists impression of a binary star system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... White dwarf Sirius-B in x-rays A white dwarf is an astronomical object which is produced when a low or medium mass star dies. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... {alternateuses}} Artists conception of a white dwarf star accreting hydrogen from a larger companion A nova (pl. ... Gravity is a force of attraction that acts between bodies that have mass. ... Potential energy is stored energy. ...
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.[2] 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.[3],(S&T) Luminosity has different meanings in several different fields of science. ... // The Hubble Telescope The Hubble Space Telescope (HST) is a telescope in orbit around the Earth. ... A standard candle is an astronomical object that has a known luminosity. ...
There are currently three known types of dwarf novae:
1.) Z Camelopardalis stars, which temporarily "halt" at a particular brightness below their peak.
2.) SU Ursae Majoris stars, which have "superoutbursts" which are brighter than the average.
3.) U Geminorum stars, which include all dwarf novae outside the previous two categories.[4], [5]
References:
"Calibrating Dwarf Novae". Sky & Telescope, September 2003, p. 20.
Astronomers estimate that perhaps about a dozen novae occur in the Milky Way, the Earth's galaxy, each year, but two or three of them are too distant to be seen or are obscured by interstellar matter.
Novae are named according to the year of their occurrence and the constellation in which they appear.
Novae in general show a relationship between their maximum brightness and the time they take to fade by a certain number of magnitudes.
A nova is a star that suddenly increases greatly in brightness and then slowly fades, but may continue to exist for some time.
The remaining star is typically a white dwarf and is commonly thought to be the smaller member of a binary (two-star) system, subject to a continuous infall of matter from the larger star.
This is perhaps always the case with dwarfnovae, which erupt repeatedly at regular intervals of a few to hundreds of days.
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