Studies of galaxy surveys in the context of the cold dark matter paradigm have shown that the mass of the dark matter halo and the total stellar mass are coupled through a function that varies smoothly with mass. Their average ratio Mhalo/Mstars has a minimum of about 30 for galaxies with stellar masses near that of the Milky Way (approximately 5 × 1010 solar masses) and increases both towards lower masses and towards higher masses. The scatter in this relation is not well known; it is generally thought to be less than a factor of two for massive galaxies but much larger for dwarf galaxies. Here we report the radial velocities of ten luminous globular-cluster-like objects in the ultra-diffuse galaxy NGC1052–DF2, which has a stellar mass of approximately 2 × 108 solar masses. We infer that its velocity dispersion is less than 10.5 kilometres per second with 90 per cent confidence, and we determine from this that its total mass within a radius of 7.6 kiloparsecs is less than 3.4 × 108 solar masses. This implies that the ratio Mhalo/Mstars is of order unity (and consistent with zero), a factor of at least 400 lower than expected. NGC1052–DF2 demonstrates that dark matter is not always coupled with baryonic matter on galactic scales.

中文翻译：

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一个缺乏暗物质的星系

在冷暗物质范式背景下的星系调查研究表明，暗物质晕的质量和恒星总质量通过一个随质量平滑变化的函数耦合。对于恒星质量接近银河系（大约 5 × 1010 太阳质量）的星系，它们的平均 Mhalo/Mstars 比率最小值约为 30，并且朝着较低质量和较高质量的方向增加。这种关系的分散性尚不清楚。通常认为，对于大质量星系，它小于两倍，但对于矮星系则要大得多。在这里，我们报告了超扩散星系 NGC1052-DF2 中十个发光的球状星团状物体的径向速度，该星系的恒星质量约为 2 × 108 太阳质量。我们推断它的速度色散小于 10。每秒 5 公里，置信度为 90%，我们由此确定它在 7.6 秒差距半径内的总质量小于 3.4 × 108 太阳质量。这意味着 Mhalo/Mstars 的比率是统一的（并且与零一致），比预期的因子至少低 400。NGC1052-DF2 表明暗物质并不总是与星系尺度上的重子物质耦合。