We review observations of ultraluminous X-ray sources (ULXs). X-ray spectroscopic and timing studies of ULXs suggest a new accretion state distinct from those seen in Galactic stellar-mass black hole binaries. The detection of coherent pulsations indicates the presence of neutron-star accretors in three ULXs and therefore apparently super-Eddington luminosities. Optical and X-ray line profiles of ULXs and the properties of associated radio and optical nebulae suggest that ULXs produce powerful outflows, also indicative of super-Eddington accretion. We discuss models of super-Eddington accretion and their relationship to the observed behaviors of ULXs. We review the evidence for intermediate-mass black holes (IMBHs) in ULXs. We consider the implications of ULXs for super-Eddington accretion in active galactic nuclei, heating of the early Universe, and the origin of the black hole binary recently detected via gravitational waves.

中文翻译：

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超亮 X 射线源

我们回顾了对超亮 X 射线源 (ULX) 的观察。ULX 的 X 射线光谱和时间研究表明，一种新的吸积状态不同于在银河系恒星质量黑洞双星中看到的吸积状态。相干脉动的检测表明在三个 ULX 中存在中子星吸积体，因此显然是超爱丁顿光度。ULX 的光学和 X 射线线剖面以及相关的射电和光学星云的特性表明 ULX 产生强大的外流，这也表明超爱丁顿吸积。我们讨论了超级爱丁顿吸积模型及其与观察到的 ULX 行为的关系。我们回顾了 ULX 中中等质量黑洞 (IMBH) 的证据。我们考虑 ULX 对活动星系核中超爱丁顿吸积的影响，早期宇宙的加热，