白矮星的平衡质量上限

本文主要根据白矮星的理想模型和白矮星的平衡条件,系统地、详细地导出了Emden方程,然后用Emden方程的解计算了白矮星的平衡质量上限,也即钱德拉塞卡质量Mc=1.4M⊙,M⊙代表太阳质量,M_C叫做钱德拉塞卡极限。只有当白矮星的质量小于M_C时,白矮星才是稳定的。     

基于相对论简并费米气体模型的Chandrasekhar极限

利用简并费米统计理论,并考虑到电子运动的相对论效应,求出白矮星的极限质量-Chandrasekhar极限质量,并进一步讨论了这一极限质量在恒星演化过程中的意义。     

热白矮星的质量-半径关系

研究了有限温度条件下分别由Fe核和C核构成的热白矮星.结果表明随着温度升高,对应同一质量的白矮星的半径增加.温度对白矮星质量-半径关系的影响强度随着星体质量的增加而减弱.相比于Fe-白矮星,C-白矮星的质量-半径关系对温度的依赖程度较大.存在一个临界质量,当白矮星的质量小于这个临界值时,温度的影响将不能忽略.C-白矮星...     

走近黑洞（下篇）

黑洞篇：恒星的质量上限 质量超过一定极限就会形成黑洞!？ 存在着黑洞的依据 按照科学家现在对恒星的认识．恒星在其寿命终结以后将变为白矮星、中子星或者黑洞。这其中的黑洞是在1916年根据广义相对论利用数学推导出来的一种天体．在那以后的15年间只是理论上的存在．     

一个实际存在的负能谱系统--白矮星

详细地剖析了初期演化过程中的白矮星的基本特性．在此基础上进一步论述了白矮星是一个实际存在的负能谱系统．     

北京师范大学天文系学者基于LAMOST巡天数据发现4颗新的DA型脉动白矮星

<正>近期,北京师范大学天文系博士后苏杰和付建宁教授等基于我国大科学装置郭守敬望远镜(又称LAMOST)巡天数据的白矮星星表,观测发现了4颗新的DA型脉动白矮星.白矮星是中、小质量恒星演化的晚期阶段,是一种由电子简并态物质构成的致密天体.由于银河系中大约98%的恒星最终都会演化成为白矮星,因此白矮星的研究对于认识和了解恒星演化规律以及银河系演化历史具有重要意义,同时白矮星也是研究极端条件下物理现象和规律的天然实验室,而DA型白矮星则是所     

白矮星系统--正能谱电子系统与负能谱氦离子系统的复合系统

本文应用正、负能谱系统热力学理论较仔细地分析了白矮星的初期演化过程，其结果虽然与过去有关理论在力学平衡问题上的结论一致，但本文所依据的基础和思路与过去理论大不相同，按原有理论，认为白矮星只是一个高度简并的电子系统，而氦离子系统仅作为约束电子系统的外部条件，显然这个理论模型不能反映白矮星的实际状态，因为白矮星并非一个电子系统。而是由电子与氦离子组成的复合系统。因此，原有理论除了可以描写电子系统的力学平衡外，它根本不可能描述白矮星的演化，本文将白矮星视为电子系统与氦离子系统的复合系统。不仅可以描述白矮星的力学平衡，而且还可通过熵的演化来描写白矮星的演化进程。     

重复快速射电暴FRB 121102白矮星和中子星双星模型的再研究

快速射电暴(FRB)是宇宙中忽然出现的短暂而明亮的射电爆发现象,它的物理起源至今还是一个谜.重复快速射电暴可能源于一个具有强偶极磁场的中子星和磁化的白矮星组成的致密双星系统.当白矮星充满它的洛希瓣时,物质将会通过拉格朗日点从白矮星转移到中子星.一次爆发之后,白矮星可能被踢开.对于唯一已知的重复暴源FRB 121102,总共探测到41次重复爆发.用已知的红移数据,根据41次重复爆发的数据,我们再次研究了白矮星-中子星的双星模型,肯定了这样一个间歇的洛希瓣外流机制可能可以解释FRB 121102的重复爆发行为,并且相邻爆发的时间间隔和其后的暴的流量之间不存在相关性,这也与我们的洛希瓣外流机制相符.     

相对论色散关系与白矮星半径的量子引力修正效应

研究狭义相对论中的变形色散关系,得到Lorentz破缺和光速变化的关系,分析量子引力放大效应作用下光速的变化.另外,根据修正色散关系计算白矮星的半径-质量关系式.文献(Amelino-Camelia G.Living Rev Relati,2013,16(2):7-105.)指出白矮星半径的变化可能存在一些观测效应,但他们并没有讨论这些效应的物理根源,研究结果表明:在放大效应或极高密度情况时,白矮星半径的改变才比较明显.     

暗弱白矮星的CSST主巡天多色测光和无缝光谱观测预研究

中国空间站工程巡天望远镜(China Space Station Telescope, CSST)计划于2024年发射,将主要开展高空间分辨率、天区大面积(约17500平方度)的多色成像与无缝光谱巡天,预计可极大地提高白矮星的观测样本数量.本文分别基于盖亚第三次早期数据发布(Gaia EDR3)和斯隆数字巡天第十六次数据发布(SDSS DR16)探测到的白矮星候选体和已确认的白矮星样本,进行统计分析,得出恒星参数的分布(多波段星等、有效温度、表面重力加速度、距离和质量),并分析各参数之间的相关性,计算白矮星的空间密度;最后,结合CSST的观测性能,预计其将探测到的白矮星数目,为基于CSST主巡天数据开展大样本暗弱白矮星搜寻和研究工作提供预估和分析.     

Survival of a brown dwarf after engulfment by a red giant star

Many sub-stellar companions (usually planets but also some brown dwarfs) orbit solar-type stars. These stars can engulf their sub-stellar companions when they become red giants. This interaction may explain several outstanding problems in astrophysics but it is unclear under what conditions a low mass companion will evaporate, survive the interaction unchanged or gain mass. Observational tests of models for this interaction have been hampered by a lack of positively identified remnants-that is, white dwarf stars with close, sub-stellar companions. The companion to the pre-white dwarf AA Doradus may be a brown dwarf, but the uncertain history of this star and the extreme luminosity difference between the components make it difficult to interpret the observations or to put strong constraints on the models. The magnetic white dwarf SDSS J121209.31 + 013627.7 may have a close brown dwarf companion but little is known about this binary at present. Here we report the discovery of a brown dwarf in a short period orbit around a white dwarf. The properties of both stars in this binary can be directly observed and show that the brown dwarf was engulfed by a red giant but that this had little effect on it.     

一个关于白矮星力学平衡的新理论

将一个新理论——正、负能谱(PNES)热力学理论应用于白矮星系统的力学平衡问题，对白矮星初期淡化阶段的力学平衡进行了详细的分析．虽然应用PNES热力学理论所得出的结论与原有的理论结果一致．但是PNES理论的基本原理和思路与原有的理论完全不同，按照原有理论，白矮星系统只是一种电子系统，氮离子系统只被视为约束电子系统的外部约束条件．显然原有理论不能反映白矮星的实际状态，因为白矮星并不是一个电子系统而是一个由电子子系和氯离子子系组成的复合系统．因此，对白矮星的力学平衡问题和演化问题都必须以由电子子系和氮离子子系组成的复合系统来进行研究．本文应用这一新理论(PNES热力学理论)，以复合系统的观点研究了白矮的力学平衡问题．     

An ancient nova shell around the dwarf nova Z Camelopardalis

Cataclysmic variables (classical novae and dwarf novae) are binary star systems in which a red dwarf transfers hydrogen-rich matter, by way of an accretion disk, to its white dwarf companion. In dwarf novae, an instability is believed to episodically dump much of the accretion disk onto the white dwarf. The liberation of gravitational potential energy then brightens these systems by up to 100-fold every few weeks or months. Thermonuclear-powered eruptions thousands of times more luminous occur in classical novae, accompanied by significant mass ejection and formation of clearly visible shells from the ejected material. Theory predicts that the white dwarfs in all dwarf novae must eventually accrete enough mass to undergo classical nova eruptions. Here we report a shell, an order of magnitude more extended than those detected around many classical novae, surrounding the prototypical dwarf nova Z Camelopardalis. The derived shell mass matches that of classical novae, and is inconsistent with the mass expected from a dwarf nova wind or a planetary nebula. The shell observationally links the prototypical dwarf nova Z Camelopardalis with an ancient nova eruption and the classical nova process.     

The binary progenitor of Tycho Brahe's 1572 supernova

The brightness of type Ia supernovae, and their homogeneity as a class, makes them powerful tools in cosmology, yet little is known about the progenitor systems of these explosions. They are thought to arise when a white dwarf accretes matter from a companion star, is compressed and undergoes a thermonuclear explosion. Unless the companion star is another white dwarf (in which case it should be destroyed by the mass-transfer process itself), it should survive and show distinguishing properties. Tycho's supernova is one of only two type Ia supernovae observed in our Galaxy, and so provides an opportunity to address observationally the identification of the surviving companion. Here we report a survey of the central region of its remnant, around the position of the explosion, which excludes red giants as the mass donor of the exploding white dwarf. We found a type G0-G2 star, similar to our Sun in surface temperature and luminosity (but lower surface gravity), moving at more than three times the mean velocity of the stars at that distance, which appears to be the surviving companion of the supernova.     

白矮星是负熵系统

应用正、负能谱热力学理论(PNES热力学理论)，通过白矮星熵的演化对白矮星的初期演化阶段作了仔细分析，得出了白矮星在其初期收缩过程中是一个负熵系统，白矮星的演化由其正熵(电子子系的熵)Se和负熵(氮离子子系的熵)SHe之问的竞争决定，当SHe比Se增长得快时，则系统的总熵将更负，它必将更趋于有序态；反之，当SHe比Se增长得慢时，系统的负熵将减少，于是系统的有序程度将减少．     

负能谱系统的稳定性

建立了正、负能谱系统稳定性判据间的互补对应关系,在此基础上结合白矮星的自由能密度函数的具体形式,分析了白矮星(或一般负能谱)系统的稳定性.     

Infrared spectrum of an extremely cool white-dwarf star

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested to make up much of the 'dark matter' in the halo of the Milky Way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.     

Exclusion of a luminous red giant as a companion star to the progenitor of supernova SN 2011fe

Type Ia supernovae are thought to result from a thermonuclear explosion of an accreting white dwarf in a binary system, but little is known of the precise nature of the companion star and the physical properties of the progenitor system. There are two classes of models: double-degenerate (involving two white dwarfs in a close binary system) and single-degenerate models. In the latter, the primary white dwarf accretes material from a secondary companion until conditions are such that carbon ignites, at a mass of 1.38 times the mass of the Sun. The type Ia supernova SN 2011fe was recently detected in a nearby galaxy. Here we report an analysis of archival images of the location of SN 2011fe. The luminosity of the progenitor system (especially the companion star) is 10-100 times fainter than previous limits on other type Ia supernova progenitor systems, allowing us to rule out luminous red giants and almost all helium stars as the mass-donating companion to the exploding white dwarf.     

The age of the Milky Way inner halo

The Milky Way galaxy has several components, such as the bulge, disk and halo. Unravelling the assembly history of these stellar populations is often restricted because of difficulties in measuring accurate ages for low-mass, hydrogen-burning stars. Unlike these progenitors, white dwarf stars, the 'cinders' of stellar evolution, are remarkably simple objects and their fundamental properties can be measured with little ambiguity. Here I report observations of newly formed white dwarf stars in the halo of the Milky Way, and a separate analysis of archival data in the well studied 12.5-billion-year-old globular cluster Messier 4. I measure the mass distribution of the remnant stars and invert the stellar evolution process to develop a mathematical relation that links this final stellar mass to the mass of their immediate progenitors, and therefore to the age of the parent population. By applying this technique to a small sample of four nearby and kinematically confirmed halo white dwarf stars, I calculate the age of local field halo stars to be 11.4?±?0.7 billion years. The oldest globular clusters formed 13.5?billion years ago. Future observations of newly formed white dwarf stars in the halo could be used to reduce the uncertainty, and to probe relative differences between the formation times of the youngest globular clusters and the inner halo.