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M87* · EHT 2019 reference horizon: size, dimension and comparison

The adopted reference is about 3.8392E10 km.

Equivalent Schwarzschild diameter, non-rotating model

38.392 billion km ≈ 38,392 million km. One billion kilometers is 1,000 million kilometers.

A horizon scale calculated from a reference mass.

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M87* · EHT 2019 reference horizon, interpreted illustration
Interpreted illustration · dimension stated in the fact sheet.

What does this number measure?

Reference mass: 6.5e+09 solar masses, a value reported by NASA in 2019. 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 spherical, non-rotating 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 affect its appearance. The artistic ring around the reference 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 TON 618 · reference horizon in the explorer →

Source and limitations

Estimated reference mass dated 2019; it is not an exact current measurement. Explicitly 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.