*Article* **Stable Up-Down Quark Matter Nuggets, Quark Star Crusts, and a New Family of White Dwarfs**

**Lang Wang <sup>1</sup> , Jian Hu <sup>1</sup> , Cheng-Jun Xia 1,\* , Jian-Feng Xu 2,\*, Guang-Xiong Peng 3,4,5,\* and Ren-Xin Xu 6,7,\***


**Abstract:** The possible existence of stable up-down quark matter (*ud*QM) was recently proposed, and it was shown that the properties of *ud*QM stars are consistent with various pulsar observations. In this work we investigate the stability of *ud*QM nuggets and found at certain size those objects are more stable than others if a large symmetry energy and a small surface tension were adopted. In such cases, a crust made of *ud*QM nuggets exists in quark stars. A new family of white dwarfs comprised entirely of *ud*QM nuggets and electrons were also obtained, where the maximum mass approaches to the Chandrasekhar limit.

**Keywords:** quark matter; up-down quark nuggets; quark star crusts; white dwarfs
