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Sagittarius A* · reference horizon: size, dimension and comparison

The adopted reference is about 25,398,000 km.

Equivalent Schwarzschild diameter, non-rotating model

25.398 million km ≈ 25,398,000 km. One million kilometers is 1,000,000 km.

A horizon scale calculated from a reference mass.

Explore at this scale
Sagittarius A* · reference horizon, interpreted illustration
Interpreted illustration · dimension stated in the fact sheet.

What does this number measure?

Reference mass: 4.3e+06 solar masses, a value reported by NASA in 2023. We calculate D = 4 GM☉ × (M/M☉) / c² with nominal GM☉ = 1.3271244 × 10²⁰ m³/s² and c = 299 792 458 m/s. This is the diameter of a non-rotating spherical model of the same mass, not a direct measurement of the real horizon or the diameter of the shadow or bright ring photographed by the EHT. Rotation, inclination and bent light alter its appearance. The artistic ring around the reference object is not measured.

Compare the stated dimensions

The comparison uses the number in each fact sheet: altitude, height, diameter, length or distance, depending on the reference. Two values in metres do not necessarily describe the same property.

Compare with M87* · EHT 2019 reference horizon in the explorer →

Source and limitations

Reference estimated mass dated 2023; it does not describe an exact current measurement. Explicit non-rotating model. The observed shadow and the horizon are not interchangeable.

A shared conceptual cross-section of the reference horizons, not a photograph. Only the diameter of the central dark disc follows the non-rotating model's dimension; the outer emitting ring is artistic and excluded from the measurement. This disc is not the shadow observed by the EHT.