Sagittarius A*
Sagittarius A* — the supermassive black hole at the centre of the Milky Way, about 4.3 million times the Sun's mass, ~26,700 light-years away. In 2022 the Event Horizon Telescope imaged the glowing ring of hot gas around its shadow. It is the anchor of the S-star cluster: dozens of stars on tight, fast orbits, two of which are mapped here — S2, which confirmed Einstein's relativity near the hole, and S301, whose orbit is the shortest and fastest yet measured.
Science
Classification
- Type
- Supermassive black hole
- Location
- The Galactic Centre, in Sagittarius
- Distance
- ~26,700 light-years
- GRAVITY Collaboration 2019
Physical
- Mass
- ~4.15 million solar masses
- stellar orbits (Genzel & Ghez) + EHT 2022
- Event-horizon width
- ~2.5×10⁷ km · ~17 Suns wide — computed from the mass (Schwarzschild radius)
- Shown here
- an enlarged marker · the real hole is far too small to see at galaxy scale
How we know
- Note
- The 2022 Event Horizon Telescope image is an interferometric RECONSTRUCTION from radio (VLBI) data — telescopes across the planet combined into one image, model-dependent by the collaboration's own account — not a photograph. It shows the ring of hot gas bent around the black hole's shadow, not the hole itself (a black hole emits no light). Its mass comes from decades of tracking stars orbiting an invisible point (2020 Nobel Prize). Its size here is an enlarged marker for the galactic centre; the true event horizon is only ~2.5×10⁷ km across.
Discovery & history
- Method
- Telescope
- Name
- 'Sagittarius A*' — the compact radio source in the constellation Sagittarius; the asterisk (star) marks it as the exciting, point-like core.
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 Event Horizon Telescope imaged its shadow in 2022.
Images
Images from open archives · credit shown per image