There were many newspaper headlines over the last week or so that outlined the research done by Marco Ajello, an astrophysicist at the Clemson College of Science in South Carolina. They all claimed that the total starlight ever created - by any star in any galaxy - had been 'measured'. I took this with a pinch of salt: surely they meant that it had been calculated, rather than measured. How could we be taking measurements of the light emitted from long dead stars? Or for small, distant stars? Surely we are looking at pretty crude calculations based on rough approximations, all based on simplistic assumptions?
So I did a little background reading. And for once my scepticism at the big claims made by newspapers on behalf of scientists seem to have been unjustified.
The research apparently used readings taken from the Fermi Gamma Ray Space Telescope (pictured). The light from distant and small stars may not be detectable directly, but it will always find its way into the EBL (the extragalactic background light), a cosmic fog composed of all the ultraviolet, visible and infrared light emitted by stars. The Clemson researchers were basing their work on images taken by Fermi of this background light.
I'm sure some extra calculations had to be done, but they would have been based on actual observations rather than guesswork, which seems to justify the headlines. It seems to me a remarkable achievement.
And how much light has ever been created by the stars? 4 x 10(exp84) photons.
https://www.sciencedaily.com/releases/2018/11/181129142414.htm