FSR 1758

FSR 1758
Observation data (J2000 epoch)
Constellation	Scorpius
Right ascension	17h 31m 12s
Declination	−39° 48′ 30″
Distance	11.5 kpc (38 kly)
Apparent magnitude (V)	<7
Apparent dimensions (V)	1.56 ± 0.44 °
Physical characteristics
Absolute magnitude	<–8.6
Mass	~107 M☉
Radius	10 ± 1 pc
Tidal radius	150 ± 45 pc
Metallicity	${\begin{smallmatrix}\left[{\ce {Fe}}/{\ce {H}}\right]\end{smallmatrix}}$ = −1.5 dex
Notable features	Possible nucleus of a dwarf galaxy

FSR 1758 is a large and bright but heavily obscured globular cluster belonging to the Milky Way galaxy. It is located at a distance of about 11.5 kpc from the Sun and about 3.7 kpc from the center of the galaxy. As FSR 1758 lies behind the galactic bulge it is heavily obscured by the foreground stars and dust. It was first noticed in 2018 in Gaia data although it was listed in some catalogs as a diffuse open cluster since at least 2007.

The size and brightness of FSR 1758 may be comparable or exceed those of the Omega Centauri cluster, which is widely believed to be the nucleus of a dwarf galaxy that merged into Milky Way in the past. Therefore, FSR 1758 may be the nucleus of dwarf galaxy tentatively named Scorpius Dwarf galaxy. It can also be similar to another globular cluster Messier 54, which is known to be the nucleus of Sagittarius Dwarf Spheroidal Galaxy.