Isosurface of the ALFALFA Virgo 7 hydrogen cloud (a.k.a. the Kent Complex). This is an enormous hydrogen cloud in the Virgo galaxy cluster and its origins are poorly understood. Unlike other hydrogen clouds, it’s not connected to any galaxies, and there are no galaxies aligned with the cloud that are likely to be its parent. It has no detectable stars but over a billion times the mass of the Sun in gas.
This model was created using data from the recent Widefield Arecibo Virgo Extragalactic Survey, the most sensitive observations of the complex to date (it shows the velocity structure of the cloud, not its true 3D shape). These revealed connections between individual clouds within the complex that were not previously seen, as well as detecting 50% more gas. That makes it harder to explain - its mass is so large that none of the original gas seems to have evaporated, unlike in other such tails. And that’s weird.