The star that hosts the first directly imaged multi-planet system is HR 8799. In 2008, astronomers announced infrared images of three giant planets orbiting HR 8799, and later observations revealed a fourth planet closer to the star.
HR 8799 is a young main-sequence star about 133 light-years away in the constellation Pegasus. Its planets are unusually suitable for direct imaging because they are massive, widely separated from their star, and still hot from their formation. Their strong infrared glow helps astronomers distinguish them from the much brighter starlight.
The discovery marked a major change in exoplanet astronomy. Most planets are detected indirectly, through a star’s wobble or a dip in its brightness during a transit. Direct imaging instead captures light from the planet itself, although advanced adaptive-optics and image-processing techniques are needed to suppress the host star’s glare.
Fomalhaut is a common mix-up because it also has a famous directly imaged companion, Fomalhaut b. That system did not establish the first directly imaged multi-planet system. HR 8799’s four known giant planets also provide a rare laboratory for studying the atmospheres and orbital motion of several worlds around one star.