致密星是白矮星、中子星、奇特星、黑洞等一类致密天体的总称，它们与正常星的主要区别是不再有核燃料进行聚变反应，热压力不足以与自身的引力保持平衡，因而塌缩成尺度非常小、密度非常大的天体。致密星通常是恒星演化末期的终结形态，恒星演化为何种致密星主要取决于恒星的质量。一般来说，质量在1倍至6倍太阳质量的恒星最终演化成白矮星，并伴随有质量损失，其外壳向外抛出，形成行星状星云。质量为3至8倍太阳质量的恒星演化成中子星，更大质量的恒星则坍缩成黑洞。

In astronomy, the term compact star (sometimes compact object) is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes.

Most compact stars are the endpoints of stellar evolution and are thus often referred to as stellar remnants, the form of the remnant depending primarily on the mass of the star when it formed. These objects are all small in volume for their mass, giving them a very high density. The term compact star is often used when the exact nature of the star is not known, but evidence suggests that it is very massive and has a small radius, thus implying one of the above-mentioned categories. A compact star that is not a black hole may be called a degenerate star.