Mereghetti S, Tiengo A, Esposito P, La Palombara N, Israel G L, Stella L
Istituto Nazionale di Astrofisica-Istituto di Astrofisica Spaziale e Fisica cosmica di Milano, via E. Bassini 15, 20133 Milano, Italy.
Science. 2009 Sep 4;325(5945):1222-3. doi: 10.1126/science.1176252.
White dwarfs typically have masses in a narrow range centered at about 0.6 solar mass (M(o)). Only a few ultramassive white dwarfs (mass > 1.2 M(o)) are known. Those in binary systems are of particular interest, because a small amount of accreted mass could drive them above the Chandrasekhar limit, beyond which they become gravitationally unstable. Using data from the x-ray multimirror mission (XMM)-Newton satellite, we show that the x-ray pulsator RX J0648.0-4418 is a white dwarf with mass > 1.2 M(o), based on dynamical measurements only. This ultramassive white dwarf in a post-common envelope binary with a hot subdwarf can reach the Chandrasekhar limit, and possibly explode as a type Ia supernova, when its helium-rich companion will transfer mass at an increased rate through Roche lobe overflow.
白矮星的质量通常集中在一个狭窄的范围内，中心约为0.6个太阳质量（M⊙）。已知的超大质量白矮星（质量>1.2 M⊙）只有少数几颗。处于双星系统中的白矮星特别令人感兴趣，因为少量吸积的物质可能会使它们超过钱德拉塞卡极限，超过该极限后它们就会变得引力不稳定。利用来自X射线多镜面任务（XMM）-牛顿卫星的数据，我们仅基于动力学测量就表明，X射线脉动源RX J0648.0-4418是一颗质量>1.2 M⊙的白矮星。这颗处于后共包层双星系统中、与一颗热亚矮星相伴的超大质量白矮星，当其富含氦的伴星通过洛希瓣溢流以增加的速率转移物质时，能够达到钱德拉塞卡极限，并有可能作为Ia型超新星爆发。
