GQ Lupi b

GQ Lupi b, or GQ Lupi B, is a possible extrasolar planet, brown dwarf or sub-brown dwarf orbiting the star GQ Lupi. Its discovery was announced in April 2005, less than a month before the full confirmation of 2M1207b was announced. Along with 2M1207b, this was one of the first extrasolar planet candidates to be directly imaged. The image was made with the European Southern Observatory's VLT telescope at the Paranal Observatory, Chile on June 25, 2004.

GQ Lupi b has a spectral type between M6 and L0, corresponding to a temperature between 2050 and 2650 kelvins. Located at a projected separation of about 98 AU from its companion star, its orbital period is estimated to be around a millenium. Because the theoretical models which are used to predict planetary masses for objects in young star systems like GQ Lupi b are still tentative, the mass cannot be precisely specified — models place GQ Lupi b's mass anywhere between a few Jupiter masses and 36 Jupiter masses, with a best estimate of ~. At the higher end of this range, GQ Lupi b could be classified as a small brown dwarf, but at the lower end of this range, it could be classified as an extremely large Jupiter-like exoplanet rather than a brown dwarf. Recent estimates made in the 2020s still place it at a most likely mass of --, which would make it a brown dwarf, while several determined mass ranges still extend into the planetary mass regime.
As of 2006, the International Astronomical Union Working Group on Extrasolar Planets described GQ Lupi b as a "possible planetary-mass companion to a young star." GQ Lupi b is listed as a "confirmed planet" as of 2020.

Accretion disk

Emission by hydrogen in the near-infrared was first detected in 2007 with the Very Large Telescope. This was interpreted as a sign of accretion of material from a disk. Additionally H-alpha emission was detected with Hubble. H-alpha was also detected with the Magellan Telescope, but the disk was not detected with ALMA. An analysis of additional VLT data showed a mutual inclination with the circumstellar disk of 84 ± 9°. This hints to a turbulent formation of the disk around GQ Lupi b. The researchers suspect the disk to be in a transitional stage in which satellites opened a gap within the disk, indicating a late stage of the disk. The accretion rate was estimated to be 10^−6.5 /year. A study from 2023 with additional VLT data found the emission line to be variable on timescales of several months to decades. The observations were consistent with magnetospheric accretion. Mid-infrared observations with JWST MIRI did not show any silicate features from the disk. This indicates grain growth and dust settling. Additionally the disk could have an inner cavity that is larger than allowed by sublimation.