

Black Hole Hunters - davesque
http://www.nytimes.com/2015/06/09/science/black-hole-event-horizon-telescope.html

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wkcamp
Is it not possible to look at the accretion disk with a telescope and then
make the calculations for the Event Horizon radius (Schwartzchild radius), etc
of the black hole? Or do some black holes not have accretion disks?

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Trombone12
Not in the optical if that's what you mean, and not in most of the rest of the
spectrum, there's a lot of dust between us and Sgr A*.

But looking at the accretion disk is exactly what the EHT is doing, just in
microwaves since those can be seen clearly trough the dust.

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Trombone12
Very exciting to see the EHT taking data again!

Too bad it sounds like they didn't get a great run, but hopefully they got
enough baselines to combine with the old data and get a picture! :DDD

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davesque
Imaging the event horizon of a black hole would be a watershed moment. I
really want to see this happen.

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themartorana
But you can only image millimeters before it, right? It still wouldn't show
what happens at the event horizon, would it? Or am I wrong? (Armchair
physicist as best, so correct me where I'm wrong, please.)

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sliken
Sure, but we've not seen an acretion disk so far, only the resulting jets. But
by definition we can only see up to the event horizon, not the horizon itself
or beyond.

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ars
You can't see the edge of the event horizon either - time is stopped at such a
place. And slightly farther away events happen so slowly they are invisible at
human time scales.

Even far from a black hole it would be almost impossible see anything. All the
light would be red shifted to invisibility (because of the intense
gravitational field), and the brightness would be very low because it's
happening so slowly.

I suspect that some of the very red, very dim, galaxies that are assumed to be
very distant because they are hubble-red-shifted so much, are actually super-
massive objects.

