Most black holes are 100 solar masses or less. M87 in the pictures was 6.5 billion solar masses, and SagA* is around 4 and a half million solar masses (or thereabouts). The event horizon of a black hole is proportional to its mass, so any other observable black hole would need to be that proportional distance closer to us. It's possible, but I'm not sure how we can identify them. We could only prove that SagA* existed because we saw stars whipping around a piece of empty space at ridiculous speeds. Also, I presume smaller black holes would either have no accretion disks, or dim ones.
Also we're not looking at "light", we're looking at radio waves...but not really an important distinction. I'm not certain of this, but I don't think we could observer ANYTHING with visible light in the area. They needed to use radio waves because those can penetrate the physical barriers that would otherwise obscure the area. The radio waves are created by the accretion disk itself. The accretion disk is super-high energy particles blasting EMR in every direction. The pattern of the black hole image is the radiation from the accretion disk being warped towards us by the intense gravity. It's not a reflection. It's actual photons traveling around a highly curved bit of spacetime and then "escaping" to a flatter piece of spacetime and making their way to us. (The photons themselves would perceive their travel to be in a straight line, by the way, they are just travelling through curved space-time. One of the fun things about this observation is that we are looking at the limits of general relativity. Our normal lives don't really expose us to anything but more "conventional" aspects of relativity. But when you look at that image, it's not just accretion disks and donut holes - it's actual spacetime getting up to absolute fuckery. And you're looking at it. Amazing. The closest we get to any truly relativistic conditions is the adjustments our GPS satellites have to make to their internal clock speeds to account for their high velocity changing the rate at which they experience time.)
There would also be some light from behind the black hole getting "lensed" around it , creating an additional ring of photons that have arrived at the black hole from other stars.
I don't really find it all that intriguing to look up at the stars. Anything that I can observe in a telescope from my backyard I can see much better with google image searches..ha.
As for Einstein: we actually KNOW that he is wrong. Or at least incomplete. General Relativity is incompatible with quantum mechanics (and vice versa). And basically all of modern physics is in one way or the other an attempt to determine what happens when Einstein's theories stop and quantum mechanics starts. I hope it happens in our lifetimes, but I'm not hopeful. At some point we will do some math, or observe some phenomena that are not explainable by General Relativity. But we keep on doing more extreme experiments and they still fall within the bounds of GR: LIGO detecting gravity waves, and now the observation of a black hole. I think many scientists were hoping there would be a surprise out of this observation because it might provide some insight. (It's likely that black holes and their event horizons are one of the places where the gap between GR and quantum mechanics might be most distinct.)
Einstein was even more amazing than we give him credit for. He made some assumptions that were outlandish, but was smart enough to work through them (and all of the wacky implications) within a lifetime. But he still had to make those leaps of faith, which require years to validate. I don't think even he knows why he made those assumptions and worked through the math.
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Originally Posted by Gman.45
