Announced just a few days ago (June 23), images captured by the telescope confirmed the existence of the vortex, the first one observed in the 21st century.
Neptune's dark vortices are high-pressure systems and are usually accompanied by bright "companion clouds," which are also now visible on the distant planet. The bright clouds form when the flow of ambient air is perturbed and diverted upward over the dark vortex, causing gases to likely freeze into methane ice crystals.
Observers reported seeing bright clouds on Neptune in July 2015, possible signs of companion clouds accompanying a dark vortex.
In September 2015, the Outer Planet Atmospheres Legacy (OPAL) program, revealed a dark spot close to the location of the bright clouds, which had been tracked from the ground. The new Hubble images captured May 16 confirmed OPAL's findings.