| Summary: | The possible existence of stable up-down quark matter (<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>u</mi><mi>d</mi></mrow></semantics></math></inline-formula>QM) was recently proposed, and it was shown that the properties of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>u</mi><mi>d</mi></mrow></semantics></math></inline-formula>QM stars are consistent with various pulsar observations. In this work we investigate the stability of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>u</mi><mi>d</mi></mrow></semantics></math></inline-formula>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 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>u</mi><mi>d</mi></mrow></semantics></math></inline-formula>QM nuggets exists in quark stars. A new family of white dwarfs comprised entirely of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>u</mi><mi>d</mi></mrow></semantics></math></inline-formula>QM nuggets and electrons were also obtained, where the maximum mass approaches to the Chandrasekhar limit.
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