awarehorizon // atlas_record
Sagittarius A*
Invisible itself — traced by the stars it moves.
- classification
- Supermassive black hole
- system
- Milky Way galactic centre
Sagittarius A* is the compact radio source at the centre of the Milky Way, identified as a supermassive black hole. It is the closest object of its kind, which makes it the best-studied.
- Distance from Earth
- about 26,000 light years
- Mass
- about 4.3 million solar masses
- Event-horizon radius
- roughly 12 million km (Schwarzschild radius)
- Location
- constellation Sagittarius, galactic centre
Only values with an established scientific consensus are listed. Where a quantity is uncertain or model-dependent, it is discussed in the sections below rather than stated as data.
A vast mass sits in a tiny volume
Stars orbit an unseen object at high speed on tight, closed orbits, requiring millions of solar masses within a region smaller than our solar system.
It has been imaged in silhouette
A ring of emission surrounding a central dark region was resolved in 2022, matching predictions for a black hole shadow.
It accretes faintly
Compared with active galactic nuclei, Sagittarius A* is remarkably quiet, consuming very little material.
Long-term stellar orbit tracking
Decades of infrared imaging traced individual stars through complete orbits, giving a precise central mass.
Radio interferometry
A global array of radio telescopes acted as one Earth-sized instrument to resolve the emission ring.
Multi-wavelength monitoring
X-ray and infrared flares track how material behaves close to the horizon.
- Why is its accretion rate so low compared with similar black holes?
- How do the flares originate — magnetic reconnection, orbiting hot spots, or something else?Competing hypotheses remain.
- What happens to information that crosses the horizon?An unresolved theoretical problem.
Items above are unresolved. Hypotheses are labelled as such and are not presented as confirmed findings.