[ExI] First Picture of a Black Hole!

[John Clark]

They said they're going to try to get a picture of Sagittarius A Star next
but It's not entirely clear to me why they chose M87 first. I'm just
guessing but I do know that the luminosity of a supermassive Black Hole has
more to do with the amount of gas outside that is falling into it than the
mass of the hole, and the important thing as far as pictures are concerned
is not the luminosity but the resolution. Another factor may be that
because we're in the Galaxy we have to look through it to see the center
and that means looking through lots more obscuring dust than to see the
Black Hole in M87.

John K Clark

On Wed, Apr 10, 2019 at 11:36 AM Tomaz Kristan <protokol2020 at gmail.com>
wrote:

> >  because it is about 1000 times more massive.
>
> Yeah, but Sagittarius is 2000 times closer. Per unit of mass therefore
> 4000000 million times more luminous. 4000 times more luminous in absolute
> terms.
>
> Sagittarius should be the most "luminous"  black hole for us, just as the
> Sun is the most luminous star for us.
>
> On Wed, Apr 10, 2019 at 4:34 PM John Clark <johnkclark at gmail.com> wrote:
>
>>
>>
>> On Wed, Apr 10, 2019 at 9:54 AM <spike at rainier66.com> wrote:
>>
>> > COOL!
>>>
>>> I am amazed that it is asymmetric and the thermal spectrum is so
>>> non-uniform.
>>>
>>
>> It looks asymmetric because the matter in the accretion disk is moving
>> very close to the speed of light and as it orbits some of it is going
>> toward us and some is going away so one side looks brighter than the other.
>> The inner edge of the bright part comes from the photosphere, the last
>> place where light can stably orbit and has a radius of 1.5 times
>> the Schwarzschild event horizon, however because gravity is so strong we
>> are able  to see the back side of the Black Hole too so it works out
>> that the dark part in the center of the picture is 2.6 times the radius of
>> the event horizon. To the limits of measurement it looks exactly how
>> Einstein said it should, it would have been even more exciting if it didn't.
>>
>> I assume they chose to image M87 instead of the Black Hole in the center
>> of our own galaxy because it is about 1000 times more massive.
>>
>>  John K Clark
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>
>
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