矮新星，或双子座U型变星是激变变星的一种，是有来自伴星的物质推积的吸积盘和白矮星的联星系统。它们与传统的新星相似，虽然都有白矮星周期性的爆发介入，但是机制是不同的：传统的新星是因为累积的氢融合和爆发，而矮新星是因为吸积盘的不稳定。当盘中的气体达到临界温度时，会造成黏滞性的改变，导致盘的崩溃而坠落至白矮星上，释放出大量的重力位能。

矮新星还有其它与传统新星不同的特征：它们的光度低，和从数天至数十天的周期。爆发时增加的的光度和再现的间隔与轨道周期有关；哈伯太空望远镜近来的研究认为后者（轨道周期）的关系可能使矮新星成为测量宇宙尺度距离有效的标准烛光。 ,(S&T)

A U Geminorum-type variable star, or dwarf nova (pl. novae) is a type 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. The first one to be observed was U Geminorum in 1855; however, the mechanism was not known till 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 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 a cooler, duller mode.