From Martin Savage
I was intrigued by the report of a black hole with a mass 12 billion times that of the sun, which apparently existed 12.8 billion years ago (28 February, p 14).
I can understand how the researchers estimated its distance, and therefore age, from the stretching of light wavelengths. However, the estimation of size is based on apparent brightness.
I wonder how they allowed for gravitational lensing events while the light was en route. After all, even a small lensing event 12 billion years ago would have had a large effect on apparent brightness, and therefore size, as observed now.
Jomtien, Thailand
