Galactic Centre

cluster

The Galactic Centre — the innermost few light-years of the Milky Way, where a dense cluster of stars orbits the supermassive black hole Sagittarius A*. Descend to see the black hole and two of those stars mapped from their real measured paths: S2, which tested Einstein's relativity near the hole, and S301, on the shortest and fastest orbit yet measured.

Open in 3D viewSee Galactic Centre in the live, interactive 3D map

Key facts

Central object

Sagittarius A* (black hole)

Distance

~26,700 light-years

Stars mapped

2 (S2, S301)

Science

What this is

Region: The Galactic Centre — the innermost few light-years of the Milky Way
Anchored by: Sagittarius A* — a ~4.3-million-solar-mass black hole
The 'S' cluster: Dozens of stars on tight, fast orbits around the hole
Distance: ~26,700 light-years

Mapped here

S2 (S0-2): 16-year orbit — tested general relativity; part of the 2020 Nobel Prize work
S301: 8.7-year orbit — the shortest and fastest yet measured (~8% of light speed)
Why two, not forty: Two stars told properly, from real measured orbits — not a field of unlabelled dots

How we know

Note: The stars here are unresolved points of light: their orbits are MODELS built from decades of astrometric tracking (ESO's GRAVITY interferometer and its predecessors), never images. The orbit sizes, shapes and periods are firmly measured; S301's 3-D tilt has a mirror-image alternative not yet distinguished. The black hole's own 2022 Event Horizon Telescope image is itself an interferometric reconstruction from radio (VLBI) data — computed, not a photograph — of the ring of hot gas around it, not the hole itself.

Discovery & history

Name: The Galactic Centre lies in the constellation Sagittarius; its black hole is Sagittarius A*, and the stars tightly bound to it form the 'S' (Sagittarius-A* star) cluster.

A bright, compact radio source at the galactic centre was found by Balick & Brown in 1974. Decades of tracking stars whipping around an invisible ~4-million-solar-mass point (Genzel and Ghez, 2020 Nobel Prize) proved it a black hole; the EHT imaged its shadow in 2022. That same star-tracking maps the orbits shown when you descend.

Images

S301 and other S-stars orbiting Sagittarius A* — an interferometric reconstruction from ESO's VLTI (GRAVITY), with the measured orbits drawn in. A computed image, not a photograph. — ESO / GRAVITY collaboration (CC BY 4.0) · ESO

Images from open archives · credit shown per image