Ok, after yesterday’s post, in which I told you what I still didn’t understand about the Event Horizon Telescope (EHT) black hole image (see also the pre-photo blog post in which I explained pedagogically what the image was likely to show and why), today I can tell you that quite a few of the gaps in my understanding are filling in (thanks mainly to conversations with Harvard postdoc Alex Lupsasca and science journalist Davide Castelvecchi, and to direct answers from professor Heino Falcke, who leads the Event Horizon Telescope Science Council and co-wrote a founding paper in this subject). And I can give you an update to yesterday’s very tentative figure.
First: a very important point, to which I will return in a future post, is that as I suspected, it’s not at all clear what the EHT image really shows. More precisely, assuming Einstein’s theory of gravity is correct in this context:
The image itself clearly shows a black hole’s quasi-silhouette (called a `shadow’ in expert jargon) and its bright photo-sphere where photons [particles of light — of all electromagnetic waves, including radio waves] can be gathered and focused.
However, all the light (including the observed radio waves) coming ...