[FRIAM] center of the milkyway does containt a blackhole

Fri May 13 05:57:27 EDT 2022

😍😀😁

On Fri, May 13, 2022 at 12:45 AM David Eric Smith <desmith at santafe.edu>
wrote:

> Hi Gil,
>
> Yes, several good questions, some with answers, some not known.
>
> Ok now that I got that out my system:
> I had wondered if this is the same science stunt we used to image a
> blackhole...but what are they using as a light source
>
>
> The light is actually being generated by gas or dust that spirals very
> fast around the black hole itself.  Things that swirl around a central
> object don’t move cleanly.  There is a lot of turbulence and collision, and
> they heat up.  Because the infall around BHs is so fast, they get very hot
> and glow.
>
> As for what frequencies they use to observe, I think it is an intersection
> of three considerations: 1) it has to be a wavelength long enough that the
> telescopes can get phase coherence, which I think means somewhere in the
> radio (microwave might be possible in principle, but quite difficult); 2)
> it has to be a wavelength that somewhat gets through all the dust between
> the center of the galaxy and us (I think this is the main limitation); and
> 3) it has to be some frequency that the BH actually emits.  Small ones like
> BHs from single stars might emit in X-rays, but I think the large ones in
> galaxy centers are mostly radio sources, unless they produce jets that
> create a secondary source of light.  (Check me on this; I could be way off.)
>
> and how do decide on the galaxy's center
>
>
> I think people now believe that most galaxy centers have these large BHs
> in them.  It’s remarkable that 50 years ago, that had not been suspected.
> When I was a kid, I read an old Asimov book “Quasar, quasar, burning
> bright”, in which none of this was even a main theory.
>
> was this also created by the sheer weight of the galaxy?
>
>
> This is the thing nobody knows.  They are so large, and the seem to have
> formed so early, that it doesn’t seem possible for star-sized BHs to form
> and then to merge.  BHs tend to clean out the dust from the environments
> where they are for a long time, and without extra frictions, things just
> orbit for a long time, but don’t collide.  I don’t know the details on how
> people think about this in the best version.
>
> or did a star go kaboom their good knows when and it just happened to be
> more or less dead center of the galaxy?
>
>
> It seems people believe that the gathering that forms the galaxy is
> somehow related to the formation of dense things, and eventually BHs, at
> the center.  But I don’t know.
>
> and are they all shaped like a toilet?
>
>
> They are actually among the roundest things in the universe.  The ring, I
> think, is a very special kind of orbital effects.
>
> I taught with a physics prof. In Austin who used to explain mechanics to
> students in a way I liked.  He said “The moon is falling toward the earth,
> just like an apple would.  It’s just that the moon is moving sideways, so
> it keeps missing”. And that’s all orbits are.  They’re falling inward, but
> they keep missing.
>
> Where spacetime starts to tip very strongly near the event horizon, you
> can do that with light.  There is a certain radius where light, traveling
> sideways, just goes in an orbit.  A bit further in, light shining directly
> outward never gets further out (that is the event horizon).  So I think the
> ring effect isn’t so much that the glowing gas makes any kind of a ring,
> but because there the light gets condensed into orbits, and when we look at
> it, it is the light just outside that orbital radius that eventually beams
> at us.  The orbits can be going all around the BH, covering the sphere in
> any direction, but where we look at the central region of the disk, it is
> shining “sideways”, and doesn’t eventually beam out to us in a way that
> looks like it came from there.
>
> There are images of GR models, some of which got used in that Matthew
> McConaughey movie, to suggest what it would look like if you were close by,
> and didn’t have the combination of lensing distortions, dust, and telescope
> resolution limitations.  I think it gives that ring look from any
> direction, so this doesn’t have anything to do with rotating disks.  In any
> case, if there were a disk, we wouldn’t see it face-on, because it would be
> in the same plane of the galaxy as we are.
>
> Eric
>
>
>
> On Thu, May 12, 2022 at 8:08 PM David Eric Smith <desmith at santafe.edu>
> wrote:
>
>> Yeah, good stuff.
>>
>> I’m not sure when I first heard about the ALMA upgrade that would give
>> them phase coherence across the telescopes at the frequencies the EHT is
>> using, and data archiving that would allow them to try to coherently
>> register telescopes sited all around the world.  It feels like about a
>> decade ago.  I have been waiting, since that first notice, to see this
>> picture.  The M87 image a couple years ago was the resolution of the real
>> cliffhanger — whether they could get it to work at all — but this one was
>> even 2+ years harder to push through technically.
>>
>> I don’t imagine I would want to do that work.  It seems like an
>> incredible tedious grind, made for real professionals.  But I am very glad
>> to be a consumer of the outcome.
>>
>> Eric
>>
>>
>>
>> On May 13, 2022, at 11:02 AM, Gillian Densmore <gil.densmore at gmail.com>
>> wrote:
>>
>> https://www.nytimes.com/2022/05/12/science/black-hole-photo.html
>>
>> and it looks a bit like something melting on icecream. fudge or caramel
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