In 2004, the Hubble Space Telescope spotted presumably a bright exoplanet near the star "Fomalhaut" just 25 light-years away, known as "Fomalhaut b". However, astronomers found that, from the observational data in the following years, this exoplanet is fading gradually.

Summarising the observation data from many years, astronomers think that Fomalhaut b may not be a planet. The bright spot observed by the Hubble Space Telescope might be the result of a collision of two stellar objects after all. As the debris of the stellar objects left behind after this collision slowly dispersed, the brightness of the bright spot also dropped gradually.

Aside from the decrease in brightness, the movement of Fomalhaut b did not conform to a normal planetary orbit but an escape trajectory of a group of stardust affected by its host star. This unusual trajectory also suggested what Hubble Space Telescope witnessed was a collision instead of an exoplanet.

Although it might be a little disappointing to learn that Fomalhaut b was not an exoplanet, to witness a collision between two stellar objects with the Hubble Telescope is quite a rare occasion.

More information: https://hubblesite.org/contents/news-releases/2020/news-2020-09