The black hole image's question of kind
In my latest op-ed for The Wire, where I defended the criticisms of some people who called the EHT’s black hole picture too blurry, there are two lines that aren’t entirely true. This post attempts to clarify its underlying science as well as to defend it in the immediate context of the op-ed. The lines are in bold (emphasis added):
Compared to pictures of about-to-be-eaten food on Instagram and Hubble Space Telescope’s spectacular shots of distant cosmic events, the EHT’s image of the M87 black hole is blah. But this is a profoundly useless comparison; it wasn’t ever about matching up to the Double Negative gravity-renderer, for example. There is no historical record that anyone cares about that reads “first ever 60 MP image of a black hole”; if they are, then that is a case of the bottom scraping the bottom. One MP or 60 MP or 10 GP is a question of degree. What we have here is a question of kind.
The first part of the line isn’t entirely true. One MP or even maybe 10 GP might be a question of degree, but somewhere along this resolution road, the story becomes a question of kind. This is because – alluding to one of the “cosmic coincidences” that Shep Doeleman mentioned at the NSF presser announcing the image’s release – the black hole itself was of just the right size to allow itself to be imaged by the EHT in the frequency window that the latter was interested in.
If the black hole had been any smaller, any further away or not emitting the 1.3-mm radiation, or if the EHT’s baseline wasn’t high enough to achieve the necessary resolving power, the resulting image would’ve been even blurrier. A lot of things had to fall in place for it to be possible. If one of them had been out of place, or if the image had to be less blurry by a big enough factor, astrophysicists would’ve been tasked with building an EHT with a baseline greater than Earth’s diameter, which might’ve meant putting one of the telescopes in space. And that could’ve meant a change in kind, not degree. In effect, the emboldened lines from my op-ed are out of place.
However, for as long as we’re talking about having an image of a black hole at all – as opposed to having no image – complaining that it was blurry and not sharp is at best a trivial, and at worst an illegitimate, quibble. In this one historical moment alone, that the fact that the EHT’s telescopes were each operating at full tilt to obtained their part of the final image shouldn’t matter because we’re crossing over a point of no return. Before this line, such pictures didn’t exist. After the line, there are two kinds of questions of degree: one of high/low resolution images and other of how we’re organising our telescopes – Earth- or space-based – to acquire them.
