TheSagittarius A* cluster is thecluster of stars in close orbit aroundSagittarius A*, thesupermassive black hole at the center of theMilky Way (in theGalactic Center). The individual stars are often listed as "S-stars", but their names and IDs are not formalized, and stars can have different numbers in differentcatalogues.

One of the most studied stars isS2, a relatively bright star that also passes close by Sgr A*.

As of 2020^[update], S4714 is the current record holder of closest approach to Sagittarius A*, at about 12.6 astronomical units (1.88×10⁹ km), almost as close as Saturn gets to the Sun, traveling at about 8% of the speed of light. These figures given are approximate, the formal uncertainties being12.6±9.3 au and23928±8840 km/s. Its orbital period is 12 years, but an extreme eccentricity of 0.985 gives it the close approach and high velocity.^[2]

The inferred orbits of stars around the supermassive black hole Sagittarius A* at the Milky Way's center are according to Gillessen et al. 2017,^[3] with the exception ofS2 which is from GRAVITY 2019,^[4]S62 which is from Peißker et al. Jan 2020,^[5] and S4711 up to S4715, which are also from Peißker et al., Aug 2020.^[2]

Hereid1 is the star's name in the Gillessen catalog andid2 in the catalog of the University of California, Los Angeles.a,e,i,Ω andω are standardorbital elements, witha measured inarcseconds.Tp is the epoch of pericenter passage,P is the orbital period in years andKmag is theK-bandapparent magnitude of the star.q andv are the pericenter distance inAU and pericenter speed in percent of thespeed of light,^[6] andΔ indicates the standard deviation of the associated quantities.

• Galactic Center
• Star clusters

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