In the dense Virgo galaxy cluster, astronomers have spotted six strange clouds of neutral hydrogen — gas that emits no light and is therefore invisible to ordinary telescopes. Radio telescopes can pick it up, but where it came from was unclear. The scientists pointed the VLA radio telescope at these clouds, which has sharper vision than before.

Two of the clouds turned out to be attached to tiny, dim galaxies, so faint that they are barely visible even with a powerful telescope. These galaxies are blue and consist almost entirely of gas, with few stars. Two other clouds looked like stretched-out wisps of gas slowly dispersing into the space between galaxies. The last two clouds didn't show up at all in the new image — meaning they are even more diffuse.

It seems that all these clouds are not stable dark galaxies, as some scientists had hoped, but temporary clumps of gas. They are blown out of galaxies as they plow through the dense intracluster medium, or stripped off by tidal forces during close encounters. Eventually, they will dissipate completely.